Title of Invention

"METHOD AND DEVICE FOR PROCESSING THE WASTE GAS OF AN INTERNAL COMBUSTION ENGINE"

Abstract

The invention relates to a device (15) for processing the waste gas of an internal combustion engine, comprising at least one reducing agent solution evaporator (16), a hydrolysis catalyst that is connected to the reducing agent solution evaporator (16) for hydrolysing, in particular, urea to form ammonia and a SCR-catalyst (18) for selective catalytic reduction of nitrogen oxides. The reducing agent solution evaporator (16) comprises an evaporator unit (12) for providing a gaseous mixture comprising one of the following substances: a) at least one reducing agent precursor and b) one reducing agent. An aqueous solution (45) comprising at least one reducing agent precursor can be evaporated by means of the evaporator unit (12). The SCR-catal...

Full Text

Method and device for treating the exhaust gas of an internal combustion engine The subject matter of the present invention is a method and a device for treating the exhaust gas of an internal combustion engine, in which method the content of nitrogen oxides in the exhaust gas of the internal combustion engine is reduced by means of a selective catalytic reduction. The exhaust gas from internal combustion engines has substances whose emission into the environment is undesirable. In many countries, for example, nitrogen oxides (NOx) may only be contained in the exhaust gas of internal combustion engines up to a certain limit value. In addition to engine-internal measures, by means of which the emissions of nitrogen oxides can be reduced by means of a selection of a suitable operating point of the internal combustion engine, aftertreatment methods have been established which' make a further reduction of the nitrogen oxide emissions possible. One option for further reducing the nitrogen oxide emissions is so called selective catalytic reduction (SCR). Here, a selective reduction of the nitrogen oxides to form molecular nitrogen (N2) takes place using a selectively acting reducing agent. One possible reducing agent is ammonia (NH3) . Here, ammonia is often stored not in the form of ammonia but instead, an ammonia precursor is stored, which is converted to ammonia when required. Possible ammonia precursors are for example urea ((NH2)2CO), ammonium carbamate, isocyanic acid (HCNO), cyanuric acid and the like. Urea in particular has proven to be simple to store. Urea is preferably stored in the form of a urea/water solution. Urea and in particular urea/water solution is hygienically harmless, simple to distribute and to store. A urea/water solution of said type is already marketed under the name "AdBlue". DE 199 13 462 Al discloses a method in which a urea/water solution is dosed, upstream of a hydrolysis catalytic converter, into a partial flow of the exhaust gas of an internal combustion engine. The dosing-in process takes place here in the form of droplets. When the droplets impinge on the hydrolysis catalytic converter, hydrolysis and thermolysis of the urea takes place to form ammonia, which is used as a reducing agent in an SCR catalytic converter situated downstream. The method described here has the disadvantage that the hydrolysis catalytic converter is cooled by the evaporation of the urea/water solution. In particular where large quantities of ammonia are required, it is thus possible at least in regions of the hydrolysis catalytic converter for such intense cooling to take place that, here, the hydrolysis reaction no longer takes place or no longer takes place completely. Furthermore, as a result of the locally severely discontinuous cooling of the hydrolysis catalytic converter generated on account of the evaporation of the individual droplets, said hydrolysis catalytic converter can be damaged, and in particular a catalytically active coating can become detached. Proceeding from here, it is the object of the present invention to propose a method and a device with which the disadvantages known from the prior art can be at least alleviated. Said object is achieved by means of a device and a method having the features of the independent claims. Advantageous refinements are the subject matter of the respective dependent claims. The device according to the invention for treating the exhaust gas of an internal combustion engine at least comprises: an evaporator unit, a hydrolysis catalytic converter for the hydrolysis of in particular urea to form ammonia, and an SCR catalytic converter for the selective catalytic reduction of nitrogen oxides (N0X) . The reducing agent solution evaporator comprises an evaporator unit for providing a gaseous substance mixture comprising at least one of the following substances: a) at least one reducing agent precursor, and b) a reducing agent It is possible, by means of the evaporator unit, for an aqueous solution comprising at least one reducing agent precursor to be evaporated. The SCR catalytic converter is formed in the exhaust line, while the reducing agent solution evaporator and the hydrolysis catalytic converter are formed outside the exhaust line and such that they can be connected to the latter. A particulate filter can be formed upstream of the SCR catalytic converter, which particulate filter, in operation, can likewise be traversed by the reducing-agent-containing gas flow from the hydrolysis catalytic converter. This means that, in operation, the SCR catalytic converter is regularly traversed by exhaust gas, while this is not normally the case for the hydrolysis catalytic converter and the reducing agent solution evaporator. The latter are embodied such that they can be connected to the exhaust line in such a way that a gaseous substance mixture which comprises a reducing agent can be introduced into the exhaust line, but at most small quantities of exhaust gas can penetrate into the hydrolysis catalytic converter and/or the reducing agent solution evaporator. A reducing agent precursor urea is preferably used as a precursor for the reducing agent ammonia. In conventional systems known from the prior art, the hydrolysis catalytic converter is also traversed by at least a part of the exhaust gas. This requires a hydrolysis catalytic converter of said type to have, on account of the large mass flow rate of the exhaust gas, a certain volume, often half a litre and more, and a certain surface which is to be utilized for the catalytic reaction. Said volume and said surface can be considerably smaller in a hydrolysis catalytic converter according to the present invention, since said hydrolysis catalytic converter need merely be designed to be large enough that it can convert the maximum required quantity of reducing agent precursor in the evaporated aqueous solution. Here, the mass flow rates through the hydrolysis catalytic converter are considerably lower. In the evaporator unit, during operation, an evaporation of the urea-water solution takes place. Said urea-water solution can contain yet further substances which for example reduce the freezing point of said solution. Here, it is possible for in particular formic acid and/or ammonium formate to be contained in the solution. Here, the evaporator unit is embodied such that, in operation, at least an evaporation of the urea/water solution takes place. Depending on the setting of the corresponding temperature and the corresponding quantity of urea/water solution which is supplied to the evaporator unit, it is also already possible, in addition to the pure evaporation of the urea/water solution, for at least partial thermolysis of the urea to take place to form ammonia. The reducing agent solution evaporator is formed upstream of the hydrolysis catalytic converter and the latter is formed upstream of the SCR catalytic converter, so that, in operation, the evaporated aqueous solution which comprises a reducing agent precursor and/or a reducing agent, flows from the reducing agent solution evaporator into the hydrolysis catalytic converter, where at least a partly hydrolysis takes place to form the reducing agent. The hydrolysis catalytic converter leaves a gas mixture which comprises at least reducing agent. Said gas mixture is conducted into the SCR catalytic converter and serves there as a selective reducing agent for reducing nitrogen oxides (N0X) . The internal combustion engine can be mobile or stationary. The internal combustion engine is in particular a part of a land vehicle, water vehicle or aircraft, preferably of an automobile such as in particular a passenger or utility vehicle. The hydrolysis catalytic converter and the SCR catalytic converter denote catalytic converter support bodies which are correspondingly catalytically active. Said catalytic converter support bodies in particular have coatings which are catalytically active or which contain catalytically active substances. The catalytic converter support bodies particularly preferably have ceramic coatings for example in the form of a washcoat in which the correspondingly catalytically active particles are distributed. In particular, the hydrolysis catalytic converter has a coating which comprises titanium dioxide (anatase) and/or iron-exchanged zeolites. The SCR catalytic converter particularly preferably has a coating which comprises at least one of the following components: titanium dioxide, tungstic trioxide, molybdenum trioxide, vanadium pentoxide, silicon dioxide, sulphur trioxide, zeolite. So-called honeycomb bodies in particular are used as catalytic converter support bodies, which honeycomb bodies have ducts or cavities through which a fluid can flow. It is particularly preferable for a honeycomb body to be formed as a catalytic converter support body which is constructed from ceramic and/or metallic material. One option for a honeycomb body is a honeycomb body which is composed of thin sheet metal layers, with at least one structured and one substantially smooth sheet metal layer being wound or stacked with one another, and at least one of said stacks being coiled. Other catalytic converter support bodies, for example bulk material catalytic converters, support bodies made from wire mesh or the like, are possible and inventive. Also preferable is the design in particular of a hydrolysis catalytic converter in the form of a tube which is provided on the inside with a coating which catalyses the hydrolysis of the reducing agent precursor to form reducing agent. The formation of a separate evaporator unit advantageously makes it possible to continuously ensure a defined dispensation of reducing agent without non-uniform and/or incomplete hydrolysis of the ammonia precursor to form ammonia taking place in the event of increased demand for reducing agent. According to one advantageous embodiment of the device according to the invention, the evaporator unit is connected by means of a delivery line to a reservoir for the aqueous solution, with the delivery line and the evaporator unit being connected to one another by means of a connecting unit. The connecting unit forms the interface between the delivery line and the evaporator unit. Said connecting unit is designed so as to ensure a sealed connection between the delivery line and the evaporator unit in order to avoid leakage of the aqueous solution and of the gaseous substance mixture. Furthermore, the connecting unit is designed such that, at the same time, a deposition of substances in the interior of the connecting unit, for example as a result of precipitations of components of the corresponding aqueous solution, is suppressed or occurs to such a small extent that a flow through the connecting unit remains possible. The connecting unit is preferably designed such that it can be cooled. Said connecting unit is for example connected to a corresponding cooling element. Temperature control, that is to say cooling or heating, of the connecting unit is generally possible. According to a further advantageous embodiment of the device according to the invention, the connecting unit is formed at least partially from a material with a thermal conductivity of less than 10 W/m K (Watt per metre and Kelvin). A material with a low thermal conductivity, which is in particular lower than that of metals, advantageously permits the formation of a connecting unit which permits both a high temperature in the evaporator unit and also a low temperature in the delivery line to the evaporator unit. It is possible in particular for the delivery line to have a temperature of up to 70 *C, up to 80 °C or even up to 90 °C while the evaporator unit has a temperature of more than 300 °C, preferably more than 350°C and preferably even more than 400°C. A temperature of approximately 380°C is particularly preferable. Here, the low thermal conductivity of the material of the connecting unit in particular ensures that no excessive heating of the delivery line occurs. Such excessive heating would on the one hand lead to heat losses in the evaporator unit and could on the other hand cause an at least partial evaporation of the aqueous solution already in the delivery line, which is often undesirable. As a result of the aqueous solution being present in the delivery line, particularly reliable and precise regulation of the quantity of the aqueous solution supplied to the evaporator unit, and therefore of the quantity of ammonia provided, is possible. Here, materials are preferable whose thermal conductivity is only 2 W/m K or less, particularly preferably only 1 W/m K or less, in particular between 0.1 W/m K and 0.4 W/m K, in particular essentially 0.25 W/m K or less. In particular the connecting unit is designed such that its diameter is changing by less than 0.25 % even if flown through by pulsatile flows. Preferably the connecting unit is designed such that the diameter through which a fluid can flow is 0.5 to 6 mm in case of substantially circular shape of the region to be flown through. The diameter through which a fluid can flow is preferably 3 to 5 mm, in particular substantially 4mm. The region of the connecting unit to be flown through has preferably a cross section of 0.2 to 28 square millimeters irrespective of the shape of the region of the connecting unit to be flown through. Preferably the connecting unit comprises at least one peltier element for cooling and/or heating the connecting unit. The connecting unit is in particular galvanically isolated form the evaporator unit. According to a further advantageous embodiment of the device according to the invention, the connecting unit is designed such that a temperature gradient of 40 K/mm (Kelvin per millimetre) and greater can be maintained over a length of the connecting unit. This is obtained in particular by means of the construction from a corresponding material, by means of a coating made from a corresponding material and/or by means of a corresponding topological configuration of the connecting unit. It is alternatively or additionally possible for the connecting unit to be equipped with or connected to corresponding active or passive temperature control means which allow said temperature gradient to be maintained. A temperature gradient of 4 0 K/mm and greater advantageously permits a high temperature of 350°C or more to be maintained in the evaporator unit, with a more moderate temperature of for example 70ºC, 80°C or 90 °C being maintained in the delivery line. It is thereby possible on the one hand to ensure good and preferably complete evaporation of the aqueous solution with, at the same time, a small spatial extent of the evaporator unit, and a good capability for dosing of the aqueous solution. The formation of the connecting unit with a very low thermal conductivity and/or a very large possible temperature gradient advantageously permits the generation of a very constant temperature level within the evaporator unit without a significantly reduced temperature in the region adjacent to the connecting unit. Such a constant temperature level of the evaporator unit is advantageous since the formation of depositions within the evaporator unit can be effectively avoided or reduced in this way. According to a further advantageous embodiment of the device according to the invention, the connecting unit is constructed from at least one material comprising at least one of the following materials: a) a ceramic material and b) Polytetrafluoroethylene (PTFE) Said materials particularly advantageously have, on the one hand, a low thermal conductivity for example of less than 10 W/m K, and on the other hand advantageously permit the formation of a connecting unit with temperature gradients of 40 K/mm and greater. It is advantageous in particular when using a ceramic material to use an additional sealing and/or adhesive means in order to increase the impermeability of the connecting unit. According to a further advantageous embodiment of the device according to the invention, the hydrolysis catalytic converter has a heat capacity of at most 60 J/K. Here, the heat capacity of the hydrolysis catalytic converter is preferably understood to mean the heat capacity without any casing tube which may be formed. Such a heat capacity has the effect that the hydrolysis catalytic converter can be heated and cooled quickly. This advantageously makes it possible to use the hydrolysis catalytic converter as the regulating element, or one of several regulating elements, in a temperature regulating circuit. It has additionally been proven that, in particular when the hydrolysis catalytic converter is used not in the exhaust gas flow, that is to say in a situation in which the hydrolysis catalytic converter is not traversed by exhaust gas of the internal combustion engine, an embodiment of the hydrolysis catalytic converter other than in the exhaust system, where the hydrolysis catalytic converter can also be traversed by exhaust gas, is possible. A hydrolysis catalytic converter is even preferably formed with a heat capacity of at most 45 J/K, at most 30 J/K or even of 25 J/K and less. The hydrolysis catalytic converter comprises preferably a metallic honeycomb body made of a steel having a material code 1.4725 according to the german classification of steels and/or aluminium. It is to be understood that a steel with material code 1.4725 is in particular a steel having 14 to 16 wt.-% (weight-%) crominum, at most 0.08 wt.-% iron, at most 0.6 wt.-% manganese, at most 0.5 wt.-% silicon, 3.5 to 5 wt.-% aluminium, at most 0.3 wt.-% zirconium, the remainder being iron which can comprise usual impurities which add in particular up to at most 0.1 wt.-%. In particular the steel having a material code 1.4725 can be coated and/or bonded with aluminium. According to a further advantageous embodiment of the device according to the invention, the hydrolysis catalytic converter has a volume of less than 100 ml (millilitres). Volumes of the hydrolysis catalytic converter of from 5 to 40 ml, preferably of from 10 to 30 ml, have proven to be particularly advantageous. Said volumes are considerably smaller than the volumes of hydrolysis catalytic converters which are traversed by exhaust gas. The volume of the latter is often 500 ml and greater. The device according to the invention is therefore smaller and more cost-effective than systems known from the prior art. According to a further advantageous embodiment of the device according to the invention, the hydrolysis catalytic converter comprises a casing tube. The casing tube serves to seal off the hydrolysis catalytic converter. A design of the hydrolysis catalytic converter is preferable in which the latter is composed of a catalytically active coating which is applied to the inner side of the casing tube. It is also advantageous and preferable for the casing tube to serve as a retainer for a conventional structure, for example a honeycomb structure which fills up at least a part of the interior space of the casing tube, or else a structure composed of wire mesh or metal and/or ceramic foam. According to a further advantageous embodiment of the device according to the invention, at least one at least partially structured metallic layer is formed in the casing tube. Here, the hydrolysis catalytic converter can comprise a conventional honeycomb structure constructed from at least one structured, in particular corrugated metallic layer and if appropriate at least one further, substantially smooth metallic layer. It is alternatively possible for the hydrolysis catalytic converter to have a casing tube and, on the inner face thereof, to have a structured, in particular corrugated metallic layer which encircles the entire periphery of the casing tube at least once, but does not fill up clear parts of the cross section of the casing tube, so that a freely traversable cross section remains free in the interior of the layer. This is referred to as a so-called "hot tube". The hydrolysis catalytic converter preferably has ducts which are delimited by walls, with the walls of the ducts being at most 80 urn (micrometres) thick. Preferable here are wall thicknesses of 60 urn and less or 30 urn and less, in particular where the hydrolysis catalytic converter is formed at least partially from metallic layers which form the walls of the ducts. Said wall thicknesses have proven to be particularly advantageous, since these make it possible to form a hydrolysis catalytic converter with a small heat capacity. According to a further advantageous embodiment of the device according to the invention, the hydrolysis catalytic converter has a cell density of less than 600 cpsi (cells per square inch). In relation to conventional hydrolysis catalytic converters which are traversed by exhaust gas of the internal combustion engine, the hydrolysis catalytic converter which is not traversed by exhaust gas can be formed with smaller volumes and smaller surfaces. It is possible in particular here for a smaller cell density of the hydrolysis catalytic converter to be used, since the volume flow rate which flows through the hydrolysis catalytic converter even at full load is less than that of exhaust gas. It is thereby possible to form hydrolysis catalytic converters with relatively low cell densities of less than 600 cpsi, of less than 400 cpsi or even of less than 300 or 200 cpsi and less. According to a further advantageous embodiment of the device according to the invention, the hydrolysis catalytic converter is mechanically connected to the exhaust line, in particular flange-connected thereto. This advantageously permits a stable mechanical mounting of the device according to the invention. According to a further advantageous embodiment of the device according to the invention, the hydrolysis catalytic converter is thermally decoupled from the exhaust line. Thermal decoupling is advantageous since, in a cold-start phase of the internal combustion engine in which the exhaust line is still relatively cool, it is not necessary for the relatively large thermal mass of the exhaust line to also be heated up during the heating of the hydrolysis catalytic converter. Once the exhaust line has reached its conventional operating temperature, which can be up to 800 °C and more and is greater than the conventional operating temperature of the hydrolysis catalytic converter of approximately 350 to 450'C, it is prevented that the hydrolysis catalytic converter is heated by the exhaust line, which is if appropriate undesirable and complicates the regulation of the temperature of the hydrolysis catalytic converter. The operating temperature of the hydrolysis catalytic converter is in particular in the region of 350 to 450°C whereas the heating of the hydrolysis catalytic converter is preferably resulting from the hot vapor comprising reducing agent and/or reducing agent precursor, a further electrical heating and/or by waste heat of the evaporator unit having an operating temperature of upt to 450°C or more. According to a further advantageous embodiment of the device according to the invention, a bar-shaped heating element is formed, by means of which at least one of the following components can be heated: a) the hydrolysis catalytic converter and b) at least parts of the evaporator unit. According to a further advantageous embodiment of the device according to the invention, at least one bar-shaped heating element is formed, coaxially with respect to which is formed at least one of the following elements: a) the hydrolysis catalytic converter and b) at least parts of the evaporator unit. In this embodiment, the hydrolysis catalytic converter can preferably be embodied as an annular honeycomb body which contains a plurality of ducts between an inner casing tube, which is connected to the bar-shaped heating element, and an outer casing tube. The evaporator unit can in particular contain a metering line which is in particular wound in spiral fashion around the bar-shaped heating element. It is if appropriate possible for a further heating element to be formed outside the arrangement, so that parts of the evaporator unit and/or of the hydrolysis catalytic converter are situated between two heating elements. Particularly uniform heating can thereby take place. The bar-shaped heating element preferably has a plurality of heating zones whose temperatures can be controlled independently of one another. The bar-shaped heating element in particular has at least two zones, around which are formed, in each case in one zone, the hydrolysis catalytic converter and the evaporator unit or the metering line. In particular the zone of the evaporator unit or of the metering line is preferably sub-divided further, since different processes take place here, specifically for example heating of the liquid, evaporation of the liquid and superheating of the liquid. Accordingly, a configuration of the bar-shaped heating element with 5 or 6 zones is preferable. The boundary between said zones can preferably be adapted as a function of the quantity of aqueous solution which is to be evaporated. According to a further advantageous embodiment of the device according to the invention, the temperature of at least one of the following components can be controlled: a) at least parts of the delivery line; b) the hydrolysis catalytic converter; c) at least parts of the evaporator unit; d) a dosing line for metering the generated reducing agent to the exhaust system; and e) a metering unit, by means of which the hydrolysis catalytic converter can be connected to the exhaust line. In this context, temperature control is to be understood in particular to mean that the corresponding component(s) can be heated and/or cooled. Here, at least one of said components can be part of a regulating loop, and it is preferable for a plurality of said components to be parts of a regulating loop. It is possible in particular for the regulation of the temperature of said components to be carried out such that one of the components or a plurality of the components are used as a type of actuator. This means in particular that the temperature of only one of the components is actively controlled, and said component correspondingly sets the temperature of the respective other components by means of corresponding reaction kinetics and by means of the corresponding present fluid-dynamic conditions. According to a further advantageous embodiment of the device according to the invention, means for temperature control are formed, which means comprise at least one of the following components: a) a heating wire; b) a Peltier element; c) a cooling body; d) a bar-shaped heating element; e) a means for burning a fuel; and f) a component made of a material having a positive temperature coefficient (PTC). The Peltier element in particular can advantageously be used both for heating and for cooling the corresponding component. The cooling body advantageously has a shape which promotes the radiation of heat. The cooling body is preferably made from a material with high thermal conductivity such as in particular aluminium or another metal or a metal alloy. A Peltier element is to be understood in particular as an electrical component which, when a current is passed through it, generates a temperature difference based on the so-called Peltier effect. A Peltier element preferably comprises one or more elements made from p-doped and n-doped semiconductor material which are connected to one another alternately by means of electrically conductive material. The sign of the temperature difference is dependent on the direction of the current flow, so that both cooling and heating can be provided by a Peltier element. Here, a burner is to be understood in particular as a device for burning a fuel, in particular comprising hydrocarbons and/or hydrogen. Flameless combustion is also advantageously possible. It is to be understood that a material having a positive temperature coefficient, a so-called PTC-resistor, is in particular an electroconductive material the electric resistance of which increases with increasing temperature. These are in use in particular as so called self-regulating heating elements and are in particular made of a ceramic material, in particular a barium titanate ceramic. Alternatively, PTC resistors made of a polymeric material being doped with soot particles can be used. According to a further advantageous embodiment of the device according to the invention, at least one of the following components has a coating which catalyses the hydrolysis of urea: a) at least parts of the connecting unit; b) at least parts of a metering line for metering the gaseous substance mixture to the hydrolysis catalytic converter; c) at least parts of the evaporator unit; d) at least parts of a dosing line for metering the generated reducing agent to the exhaust system, and e) at least parts of a metering line, by means of which the hydrolysis catalytic converter can be connected to the exhaust line. By forming a coating which catalyses the hydrolysis of urea and which can be formed in particular as specified above, hydrolysis is advantageously catalysed already in one of the specified components as well as in the hydrolysis catalytic converter. This increases the conversion capacity and makes it possible for the hydrolysis catalytic converter to be formed to have a correspondingly small volume with a smaller catalytically active surface. The formation of a coating, which catalyses the hydrolysis of ammonia, in the dosing line serves in particular to ensure as complete a hydrolysis of ammonia as possible, and in particular also prevents significant proportions of a reverse reaction to form urea or another ammonia precursor. A coating which catalyses the hydrolysis of urea is to be understood in particular to mean that a metering line for metering the aqueous solution to the hydrolysis catalytic converter and/or an evaporator chamber for evaporating the aqueous solution have, at least in parts, a coating which catalyses the hydrolysis of urea. Said components can thereby already cause a partial hydrolysis of the reducing agent precursor to form reducing agent, and thereby improve the effectiveness of the hydrolysis. In addition, the hydrolysis catalytic converter can thereby be fundamentally formed with a smaller volume or with a smaller catalytically active surface than if no corresponding coating were formed on at least one of said components. The invention encompasses an embodiment of the device in which the evaporator unit and the hydrolysis catalytic converter cannot be traversed by exhaust gas, but rather only the SCR catalytic converter can be traversed by exhaust gas. This results in considerably reduced throughflow rates through the evaporator unit and the hydrolysis catalytic converter, which can advantageously be incorporated in the design in particular of the hydrolysis catalytic converter, so that the latter can be formed to be smaller and with a lower cell density than hydrolysis catalytic converters which are traversed by exhaust gas. This reduces the costs in the production of the device according to the invention in comparison to devices known from the prior art. According to a further advantageous embodiment of the device according to the invention, a metering unit is formed, by means of which the hydrolysis catalytic converter can be flow-connected to an exhaust line of the internal combustion engine. By means of the metering unit, the reducing agent substance mixture comprising at least one reducing agent is then metered to the exhaust line. The metering unit can in particular comprise the dosing line, but can also have further components. These can in particular be a passive mixing means, by means of which the introducible substances can be mixed with the exhaust gas. A passive mixing means is to be understood in particular to mean that no actively moveable mixing means is formed, but that a mixture of the substances with the exhaust gas can take place only by means of the formation of a static mixing means together with the characteristics of the exhaust gas flow and the flow of the introducible substances. It is particularly preferable for the mixing means to comprise at least one of the following components: a) a guide plate and b) a honeycomb body which is designed such that the exhaust gas can flow through it at least partially at an angle with respect to the main flow direction of the exhaust gas. Here, the guide plate can in particular project into the exhaust line. The guide plate can in particular be perforated at least in partial regions and/or have a curvature at least in partial regions. The guide plate can project into the exhaust line at an angle with respect to the longitudinal direction of the exhaust line at said point. In particular, the honeycomb body has ducts whose walls have perforations. As a result of said perforations, which can if appropriate be complemented by correspondingly formed guide structures, flow can take place at an angle relative to the duct longitudinal axis. Said honeycomb body can preferably also be of conical design. In particular, the dosing line opens out in the interior of a corresponding cutout of the honeycomb body, so that the corresponding substances can be dosed directly in the honeycomb body. According to a further advantageous embodiment of the device according to the invention, the honeycomb body has ducts and apertures which can be traversed by a fluid and connect adjacent ducts to one another. The apertures can here be smaller or larger than the conventional dimensions of a duct. According to a further advantageous embodiment of the device according to the invention, at least one of the following components: a) the metering unit and b) the exhaust line is designed such that, in operation, the opening-out region of the metering unit into the exhaust line forms a flow calming zone or dead zone. This particularly advantageously has the result that, in operation, the pressure in the exhaust line is lower than in the metering unit or in the dosing line, so that here, substantially no exhaust gas flows in the direction of the hydrolysis catalytic converter. A calming zone or dead zone is to be understood to mean a region with a lower pressure than the pressure in the metering unit and/or dosing line. This can be obtained in particular in connection with a mixing means which produces a calming zone or dead zone directly in the opening-out region, and promotes a mixture downstream of said opening-out region. According to a further advantageous embodiment of the device according to the invention, thermal insulation is formed downstream of the hydrolysis catalytic converter. The thermal insulation is preferably formed directly adjoining the hydrolysis catalytic converter. The thermal insulation prevents thermal contact with the exhaust line, so that it can on the one hand be prevented that the hydrolysis catalytic converter dissipates heat to the exhaust line and thereby cools down, and on the other hand that the exhaust line dissipates heat to the hydrolysis catalytic converter. In the extreme case, this could have the result that thermal regulation can no longer be carried out, since the exhaust line is always also heated as the hydrolysis catalytic converter is heated. According to a further advantageous embodiment of the device according to the invention, at least one of the following components comprises at least one temperature sensor: a) the metering unit; b) the hydrolysis catalytic converter; c) the SCR catalytic converter; d) the evaporator unit; e) the metering line; f) the evaporator chamber and g) a dosing line for metering the generated reducing agent to the exhaust line. The temperature of the corresponding component can be measured using said at least one temperature sensor. The temperature sensor preferably comprises a thermoresistor. The temperature sensor can preferably be connected to a power supply. The component can be heated in this way. This can for example be necessary in an emergency operating mode if substances have been precipitated in the component and block or threaten to block said component. In addition to urea and the like, said substances can also involve soot which has passed into the metering unit with exhaust gas, for example by diffusion. According to a further advantageous embodiment of the device according to the invention, a delivery means is formed, by means of which the aqueous solution can be delivered from a reservoir to the evaporator unit. The delivery means preferably comprises at least one pump. As a result of the delivery means, a constant pressure of the aqueous solution can be built up upstream of the evaporator unit, with dosing into the evaporator unit taking place through a valve. In another preferred embodiment, the pump is a dosing pump, with the dosing taking place by means of a corresponding actuation of the pump. Here, a dosing pump is to be understood as a pump allowing the metering of a defined volume per time unit or per stroke. According to a further advantageous embodiment of the device according to the invention, the pump can build up a delivery pressure which is greater than the highest possible exhaust gas pressure on the metering unit and/or on the dosing line during operation of the internal combustion engine. In this way, it can be prevented during operation that exhaust gas penetrates into the evaporator unit and/or into the hydrolysis catalytic converter. A pump is preferably used which has a delivery rate of up to 150 ml/min, preferably of up to 30 ml/min or up to 10 ml/min. A pump is preferably used whose delivery rate per second can be varied by 0.75 to 2.5 ml/s, in particular can be increased by said values. Preferably a pump is used as delivery means which can generate a metering pressure of up to 6 bar absolute preferably up to 2 bar absolute. The volume flow generated by the pump varies with at most 5% around a pretederminable nominal flow. Preferably the pump is formed such that it is possible to convey back to the reservoir in particular with a volume flow which corresponds to the conveying volume flow. According to a further aspect of the present invention, a method for treating the exhaust gas of an internal combustion engine is also proposed, which method comprises the following steps: a) providing a gaseous substance mixture comprising at least one of the following substances: al) reducing agent and a2) at least one reducing agent precursor; b) hydrolysis of the reducing agent precursor, with a reducing agent substance mixture being obtained; c) subjecting an SCR catalytic converter to the reducing agent substance mixture and the exhaust gas for the at least partial selective catalytic reduction of nitrogen oxides (N0X) contained in the exhaust gas, with a mixture of the reducing agent substance mixture with at least parts of the exhaust gas taking place after step b). The method according to the invention can be carried out in particular by means of the device according to the invention. The method according to the invention particularly advantageously permits the provision of ammonia as a reducing agent for use in the selective catalytic reduction of nitrogen oxides, with a highly dynamic method for providing the ammonia being proposed, so that it is possible to react quickly to very rapidly rising and therefore highly dynamic demands for ammonia as a result of high nitrogen oxide concentrations in the exhaust gas. The mixture of the reducing agent substance mixture with the exhaust gas after step b) means in particular that an evaporation of an aqueous solution comprising at least one reducing agent precursor takes place outside the exhaust gas flow, and an addition to the exhaust gas of the internal combustion engine takes place only after the hydrolysis of the reducing agent precursor to form the reducing agent. A variant of the method is preferable in which the reducing agent substance mixture is mixed with the entire exhaust gas of the internal combustion engine. Here, the reducing agent is preferably ammonia and a reducing agent precursor is preferably urea. According to an advantageous refinement of the method according to the invention, step a) comprises evaporation, in an evaporator unit, of an aqueous solution comprising at least one reducing agent precursor. The reducing agent precursor is preferably urea. In addition to urea, the solution can contain further substances, for example substances which lower the freezing point of the solution. These include for example ammonium formate and/or formic acid. A corresponding solution is marketed under the trade name "Denoxium". A further possibility is the use of a solution which is marketed under the trade name "AdBlue". According to a further advantageous embodiment of the method according to the invention, step b) at least partially takes place in a hydrolysis catalytic converter. Here, the hydrolysis catalytic converter comprises in particular a catalytic converter support body which is provided with a coating which catalyses the hydrolysis of ammonia. According to a further advantageous embodiment of the method according to the invention, the temperature of at least one of the following components is regulated: a) at least parts of the evaporator unit; b) the hydrolysis catalytic converter; c) a delivery line for delivering the aqueous solution; d) a metering line for metering the gaseous substance mixture to the hydrolysis catalytic converter; e) a dosing line for metering the generated reducing agent to the exhaust system and f) a metering unit, by means of which the hydrolysis catalytic converter can be flow-connected to an exhaust line of the internal combustion engine. The regulation of the temperature of at least one of said components advantageously permits precise control of the reaction kinetics with regard to the generated products and the quantity of generated products. It is for example possible to meter quantities of ammonia to the exhaust gas which are precisely matched to the present nitrogen oxide content in the exhaust gas or to a nitrogen oxide content in the exhaust gas which is forecast for a future time, in order to thereby obtain as complete a conversion as possible of the nitrogen oxides in the exhaust gas of the internal combustion engine. According to a further advantageous embodiment of the method according to the invention, the temperature of at least one of the following components is controlled: a) at least parts of the evaporator unit; b) the hydrolysis catalytic converter; c) a delivery line for delivering the aqueous solution to the evaporator unit; d) a metering line for metering the gaseous substance mixture to the hydrolysis catalytic converter; e) a dosing line for metering the generated reducing agent to the exhaust system and f) a metering unit, by means of which the hydrolysis catalytic converter can be flow-connected to an exhaust line of the internal combustion engine. As a result of the multiple reaction kinetics processes which take place during the reactions according to the invention, it can be sufficient to control the temperature of only parts of one or more of the above- denoted components or else the overall temperature of one or more of the above-denoted components. Here, temperature control is to be understood in particular to mean heating or cooling of the component. It can be sufficient here to use one or more of the above-denoted components as a type of actuator whose temperature is controlled in such a way that the temperature of the other components is correspondingly changed as a result of the reaction kinetics. According to a further advantageous embodiment of the method according to the invention, the aqueous solution is delivered through a delivery line to the reducing agent solution evaporator. Said delivery takes place in particular by means of a pump and in particular from a reservoir. In this context, it is particularly advantageous if the aqueous solution can be returned through the delivery line. This can be advantageous in particular when the corresponding system must be or is switched off. In an automobile, this can for example be the case if the driver switches off the ignition of the vehicle. In this case, the remaining ammonia present in the dosing line would pass unimpeded into the exhaust system and then gradually also into the atmosphere. This is often undesired, and therefore the emissions of ammonia and also of ammonia precursors into the atmosphere can be significantly reduced and in particular prevented by means of a return delivery from the delivery line and if appropriate also from the metering line. According to a further advantageous embodiment of the method according to the invention, up to 2.5 ml of aqueous solution are evaporated within one second. The evaporator unit is preferably designed such that up to 30 ml/min (millilitres per minute) of the aqueous solution can be continuously evaporated. With such a method, a dynamic provision of reducing agent is possible with which it is possible to convert even concentration peaks of the concentration of nitrogen oxides. According to a further advantageous embodiment of the method according to the invention, the temperature of at least one of the following components is determined before the start of a temperature control measure: a) the hydrolysis catalytic converter; b) the evaporator unit; c) a dosing line for metering the generated reducing agent to the exhaust line; and d) a metering unit, by means of which the hydrolysis catalytic converter can be connected to the exhaust line, and is aligned with at least one further temperature of another component. The other component is preferably a component which is substantially at the ambient temperature, for example an external temperature sensor of a motor vehicle, a cooling water thermometer etc. Here, the alignment preferably takes place before the evaporation of the aqueous solution is initiated. Alignment is to be understood here in particular to mean that a comparison of the two temperatures takes place, with it being possible for further factors to be incorporated. Here, it is particularly preferable if an evaporation of the aqueous solution takes place only if the temperature alignment yields that the determined temperature level and the temperature of the other component differ at most by a predefinable difference value. In predefining the difference value, it is taken into consideration in particular whether the system was in operation in a predefinable timespan and when the system was deactivated. It is also possible to predefine a timespan in which said diagnosis functions do not take place if the system was in operation within the timespan. The details and advantages disclosed for the device according to the invention can also be transferred and applied to the method according to the invention. The details and advantages disclosed for the method according to the invention can also be transferred and applied to the device according to the invention. Alternatively the device and the method according to the invention can be designed/performed such that hydrolysis catalytic converter and reducing agent solution evaporator are in use flown through by a partial flow of the exhaust. All advantageous improvements disclosed herein in which hydrolysis catalytic converter and reducing agent solution evaporator are usually in use not flown through by exhaust can be transferred to an alternative embodiment in which hydrolysis catalytic converter and reducing agent evaporator means are in use flown through by a part of the exhaust gas flow. The invention is explained in more detail below on the basis of the appended figures, without the invention being restricted to the exemplary embodiments shown therein. In the figures, in each case schematically: Figure 1 shows a device for providing a gaseous substance mixture in a first embodiment as a perspective view; Figure 2 shows the first embodiment of the device for providing a gaseous substance mixture in a sectioned view; Figure 3 shows a delivery line for delivering the aqueous solution from a reservoir to the metering line; Figure 4 shows a view of a device for the selective catalytic reduction of nitrogen oxide in the exhaust gas of an internal combustion engine; Figure 5 schematically shows a second exemplary embodiment of an evaporator unit; Figure 6 shows a device for providing a reducing agent; Figure 7 schematically shows an alternative embodiment of the evaporator unit in cross section; Figure 8 shows a detail of an opening-out point of a dosing line into an exhaust line; Figure 9 shows an exemplary embodiment of a device for providing a gaseous substance mixture, in section; Figure 10 schematically shows a device for providing a gaseous substance mixture; Figure 11 shows an example of a possible metering unit for metering the reducing agent substance mixture to the exhaust gas; Figure 12 shows a further example of a possible metering unit for metering the reducing agent substance mixture to the exhaust gas; Figure 13 shows an exemplary embodiment of a device for treating the exhaust gas of an internal combustion engine; Figure 14 shows a means for depositing droplets; Figures 15 to 18 show exemplary embodiments of evaporator units; Figures 19 and 20 show a further exemplary embodiment of a device for providing a gaseous substance mixture; Figure 21 shows a further exemplary embodiment of a device for treating exhaust gas; Figure 22 shows a detail of an opening-out region of a metering unit into the exhaust line and Figures 23 and 24 show examples for honeycomb bodies as catalytic converter support bodies. Figure 1 schematically shows a device 1 for providing a gaseous substance mixture comprising at least one of the following substances: a) at least one reducing agent, and b) at least one reducing agent precursor. These are in particular the reducing agent ammonia and the reducing agent precursor urea. The device 1 comprises a metering line 2 with a dispensing opening 3. Furthermore, means 4 for heating the metering line 2 are formed, with which means 4 the metering line 2 can be heated above a first critical temperature which is higher than the boiling temperature of water. The device 1 also comprises a reservoir (not yet shown here) which can be flow-connected to the metering line 2. That is to say in particular that a fluid stored in the reservoir, such as for example an aqueous solution comprising at least one reducing agent precursor, can, during operation, flow through the metering line 2 to the dispensing opening 3. By means of said device 1, a gaseous substance mixture can be provided which contains at least one reducing agent and/or at least one reducing agent precursor. In the present exemplary embodiment, the means 4 for heating the metering line 2 are wound in spiral fashion together with said metering line 2. In this way, a fluid flowing through the metering line 2 is heated and ultimately evaporated. As a result, a gaseous substance mixture which contains at least one reducing agent precursor is dispensed through the dispensing opening 3. Depending on the selection of the temperature of the means 4 for heating the metering line 2, at least partial thermolysis of the reducing agent precursor can even already take place in the metering line 2, so that the gaseous substance mixture dispensed through the dispensing opening also already contains reducing agent, such as for example ammonia, in addition to a reducing agent precursor such as for example urea. Furthermore, the device 1 for providing a gaseous substance mixture also comprises a measuring sensor 5, by means of which the temperature at at least one point of the metering line 2 can be measured. The measuring sensor 5 can for example be a conventional thermal element or a conventional thermoresistor. The device 1 and/or the individual components which require an electrical terminal preferably comprise a cable length for realizing the electrical terminals. A cable length is to be understood in particular to mean a cable connection which is at least half a metre, preferably at least one metre long. This allows plug-type contacts to be formed in regions which, in particular in automobiles, are exposed to only a small extent to environmental influences such as spray water, stone impacts or the like. Figure 2 shows the device 1 from figure 1 in section. It is possible to clearly see the metering line 2, through which the aqueous solution comprising at least one reducing agent precursor can flow during operation, and the means 4 for heating the metering line 2. The metering line 2 can have a constant cross section, though this can also be variable, as in the present example. Here, however, the traversable cross section of the metering line 2 is preferably between 0.75 mm2 and 20 mm2; the traversable cross section is preferably in the region of approximately 3 mm2. Said traversable cross sections have been proven to be advantageous since, on the one hand, fast and substantially complete evaporation of the aqueous solution is possible with a cross section of said type, and on the other hand, the cross section is large enough that the formation of depositions in the interior of the metering line 2 is substantially avoided. Figure 2 also shows the measuring sensor 5 for determining the temperature of the metering line 2. Here, the means 4 for heating the metering line 2 are operated in such a way that, in operation, the temperature across the length of the metering line 2 is at most 25 °C above and below a mean temperature. The mean temperature substantially corresponds here to the first critical temperature. The metering line 2 is formed in particular from a copper alloy. Figure 3 schematically shows the delivery line 6, via which the metering line 2 can, in operation, be connected to a reservoir (not yet shown here) . The delivery line 6 has means 7 for temperature control. In this exemplary embodiment, the means 7 for temperature control comprise in each case a plurality of Peltier elements 8 and a cooling body 9. The Peltier elements 8 are in each case provided with electrical terminals 10, by means of which they can be supplied with current. Here, depending on the polarity of the current, the Peltier elements 8 are used for heating or for cooling, so that basic temperature control of the delivery line 6 can be obtained with said Peltier elements 8. The cooling body 9 serves in particular to radiate heat energy if the delivery line 6 is cooled by the Peltier element(s) 8. The delivery line 6 can be connected to a further component by means of a connecting unit 11. Depending on the design of the device, said component can be the metering line 2 as already referred to above, or generally an evaporator unit 12. The metering line 2 can then be part of the evaporator unit 12. In general, the connecting unit 11 is formed at least partially from a material with a thermal conductivity of less than 10 W/m K (Watt per metre and Kelvin). The connecting unit 11 is formed in particular from a ceramic material and/or Polytetrafluoroethylene (PTFE) . The connecting unit 11 is in particular designed such that a temperature gradient of 40 K/mm (Kelvin per millimetre) and greater can be maintained over a length 57 of the connecting unit 11. This permits a method in which the evaporator unit 12 and/or the metering line 2 has a considerably higher temperature than the delivery line 6. The evaporator unit can for example have a temperature of 300'C or more, 400°C or more or of 420'C or more, and thereby lead to substantially complete evaporation of the aqueous solution within the evaporator unit 12, while the delivery line 6 has a temperature level of only 70°C or more, 80°C or more or 90°C or more in order to ensure that the aqueous solution is not yet evaporated in the delivery line 6. Figure 4 schematically shows a device 15 for treating the exhaust gas 13 of an internal combustion engine (not shown). The exhaust gas 13 of the internal combustion engine flows through an exhaust line 14. The device 15 for treating the gases 13 of an internal combustion engine comprises a reducing agent solution evaporator 16, a hydrolysis catalytic converter 17 and an SCR catalytic converter 18. In the reducing agent solution evaporator 16, an aqueous solution comprising a reducing agent precursor is evaporated. Urea in particular is used as a reducing agent precursor. The reducing agent solution evaporator 16 comprises, in this exemplary embodiment, an evaporator unit 12 comprising a metering line 2 which is heated by a means 4 for heating the metering line 2. Said metering line 2 is connected by means of a connecting unit 11 to a delivery line 6. The delivery line 6 is surrounded by means 7 for controlling the temperature of the delivery line 6, which means 7 can for example comprise one or more Peltier elements 8 and/or a cooling body 9, as shown above. The aqueous solution of at least one reducing agent precursor can be delivered by delivery means 19 from a corresponding reservoir 20 into the delivery line 6. In the evaporator unit 12, a gas is provided which comprises at least one reducing agent precursor such as for example urea and if appropriate also ammonia which has already been generated from the thermolysis of urea. Said gaseous substance mixture is introduced into the hydrolysis catalytic converter 17 formed downstream of the reducing agent solution evaporator 16. The hydrolysis catalytic converter 17 is designed such that in particular urea is hydrolysed to form ammonia by means of a corresponding catalytically active coating which is applied to said hydrolysis catalytic converter 17. In general, the hydrolysis catalytic converter 17 serves for the hydrolysis of a reducing agent precursor to form a reducing agent. The gas which leaves the hydrolysis catalytic converter 17, which gas contains a reducing agent and is referred to as a reducing agent substance mixture, is metered into the exhaust line 14 via a dosing line 21. The dosing line 21 opens out into the exhaust line 14 at a dosing opening which is situated upstream of the SCR catalytic converter 18. Formed downstream of the dosing opening 22 and upstream of the SCR catalytic converter 18 are mixing means 23 in the form of a guide plate which cause a mixture of the reducing agent substance mixture with the exhaust gas 13. The SCR catalytic converter therefore attains a mixture of reducing agent and exhaust gas which leads to a reduction of the nitrogen oxides contained in the exhaust gas 13 in the SCR catalytic converter 18. Here, a quantity of reducing agent substance mixture is preferably provided which is such that as complete a conversion of the nitrogen oxides in the exhaust gas 13 as possible can take place in the SCR catalytic converter 18. Figure 5 schematically shows a further exemplary embodiment of an evaporator unit 12. This illustration shows the evaporator unit 12 in section. The evaporator unit 12 comprises an evaporator chamber 24 which encompasses a substantially closed volume. In this exemplary embodiment, the evaporator chamber 24 has merely a first opening 25 for connecting a delivery line 6 (not shown here) for delivering the aqueous solution, and a second opening 26 for connecting a metering line 2 (not shown here) for discharging the gaseous substance mixture. Formed in the first opening 25 is a nozzle 62 as a means for dosing the aqueous solution 45 into the evaporator chamber 24. Said nozzle 62 serves to dose the aqueous solution 45 into the evaporator chamber 24. The evaporator unit 12 additionally has means for heating the evaporator chamber 24. In the present exemplary embodiment, said means are formed by corresponding heat conductors 27 which are in contact with the evaporator chamber 24. As shown here, said heat conductor 27 can be of asymmetric design, that is to say a higher density of heat conductors per unit area is formed in the regions which are situated substantially opposite the first opening 25 than in the regions which are not situated substantially opposite the first opening 25. Furthermore, said means cumulatively comprise a means 63 for burning hydrocarbons, such as for example a burner. A burner of said type can also be suitable for carrying out a flameless combustion of hydrocarbons. The evaporator chamber 24 is preferably formed from a material comprising at least one of the following materials: a) copper; b) aluminium; c) noble steel; d) a nickel-based material and e) chrome-nickel steel. The volume of the evaporator chamber 24 is preferably 1.5 to 10 cm3. In operation, the heat conductor 27 is preferably operated with a heating power of up to approximately one kilowatt per second, with the maximum heating power being fixed as a function of the application. In passenger vehicles, the maximum heating power is preferably approximately 500 to 700 W/s, and in utility vehicles, preferably approximately 1200 to 1500 W/s. The heat capacity of the evaporator chamber 24 is preferably less than 120 J/K, particularly preferably 100 to 110 J/K. The first opening 25 and the second opening 26 preferably enclose an angle of 30 to 70 °C. The aqueous solution 45 is preferably delivered at up to 150 ml/min into the evaporator chamber 24, preferably at up to 100 ml/min, particularly preferably at up to 30 ml/min. In the region of the second opening 26, the evaporator chamber 24 preferably has means with which an infiltration of droplets into the second opening 26 can be avoided. Said means are in particular means by which a gas film situated between the droplet and the wall of the evaporator chamber 24 can be penetrated. Said means are in particular projections of the walls or the like. The structures 28 can likewise be formed in this region. Furthermore, the evaporator chamber 2 4 has, in the interior, one or more structures 28 which serve to produce a larger surface for evaporating the aqueous solution. Said structures 28 are drawn relatively large in the present exemplary embodiment; here, said structures 28 can however also be a structured surface which can be obtained for example by applying a corresponding coating to the inner surface of the evaporator chamber 24. Said structures 28 can alternatively or additionally also comprise macroscopic structures which have a structure amplitude of a number of millimetres or even more. In general, said structures 28 are to be understood as means for increasing the wetting capacity of the surface of the evaporator chamber 24. Figure 6 schematically shows the first exemplary embodiment of the evaporator chamber 24 connected to an exhaust line 14. Here, the evaporator chamber 24 is provided with a casing 29. Said casing 29 is preferably formed from a corresponding thermal insulator which reduces heat losses to the environment. The means 27 for heating the evaporator chamber 24 can be connected by means of heat conductor terminals 30 to a current source (not illustrated). The evaporator unit 12 is connected by means of the second opening 26 to a hydrolysis catalytic converter 17. The hydrolysis catalytic converter 17 has means 31 for controlling the temperature of the hydrolysis catalytic converter 17, which means 31 are composed in the present exemplary embodiment of a corresponding heating wire which is wound around the hydrolysis catalytic converter 17. Formed around the hydrolysis catalytic converter 17 is a corresponding casing 32 which constitutes in particular thermal insulation of the hydrolysis catalytic converter 17 with respect to the environment in order to minimize as far as possible any occurring heat losses. In the present exemplary embodiment, the hydrolysis catalytic converter is connected directly to the exhaust line 14 by virtue of projecting into the latter. Formed in the exhaust line 14 is a corresponding bore, into which the hydrolysis catalytic converter 17 or its casing 32 can be inserted in as sealed a manner as possible. As sealed a connection as possible between the hydrolysis catalytic converter 17 and the exhaust line 14 can be produced by corresponding connecting means 33. Also formed, as passive mixing means, is a guide plate 34, by means of which the reducing agent substance mixture 35 which leaves the hydrolysis catalytic converter 17 is mixed with the exhaust gas flowing in the exhaust line 14. In operation, the evaporator unit 12 serves to produce a gaseous substance mixture from an aqueous solution which contains urea as a reducing agent precursor. The gaseous substance mixture generated in the evaporator unit 12 contains at least urea and if appropriate also already ammonia which has been generated by thermolysis of the corresponding urea. Said substance mixture is conducted via the second opening 2 6 into the hydrolysis catalytic converter 17 in which substantially complete hydrolysis of the urea takes place to form ammonia. Here, a reducing agent substance mixture 35 which comprises ammonia is generated in the hydrolysis catalytic converter. A method is particularly preferred in which 98% and more of the urea is ultimately converted to ammonia. Figure 7 schematically shows an alternative embodiment of the evaporator unit from figures 5 and 6. In contrast to the first exemplary embodiment shown above, this alternative embodiment additionally has a third opening 36. In operation, exhaust gas can be introduced into the evaporator chamber 24 in a continuous or pulsatile fashion through said third opening 36. It is possible in this way to obtain an improved distribution of the urea in the generated gas in comparison to the first exemplary embodiment. Furthermore, an evaporator unit 12 of said type can also be used for evaporating solid urea, since water is introduced into the evaporator chamber 24 by the exhaust gases of the internal combustion engine which are introduced through the third opening 36, which water can later be used in the hydrolysis catalytic converter 17 for the hydrolysis of the urea to form ammonia. Figure 8 schematically shows the opening-out point of a dosing line 21 into the exhaust line 14 as a part of a corresponding metering unit 46. Here, the dosing line 21 is surrounded by a heat conductor 38 which is also formed around the opening-out point of the dosing line 21 into the exhaust line 14. Figure 9 schematically shows, at a first intersection, a further possibility of a device 1 for providing a gaseous substance mixture comprising a reducing agent. The device 1 comprises a metering line 2, around which is wound a corresponding means 4 for heating the metering line 2, or which is wound together with said means 4. The metering line 2 and the means 4 for heating the metering line 2 are formed together in a common casing 29. A first temperature measuring sensor 39 is formed within the winding of the metering line 2. Said first temperature measuring sensor 39 can be connected by means of a first connecting element 40 to a corresponding control unit (not shown here). The evaporator unit 12 is connected by means of the dispensing opening 3 of the metering line 2 to a hydrolysis catalytic converter 17. The hydrolysis catalytic converter 17 has a coating which catalyses the hydrolysis of urea to form ammonia. The hydrolysis catalytic converter 17 is surrounded by means 31 for controlling the temperature of the hydrolysis catalytic converter, which means 31 comprise a correspondingly formed heating wire. Said means 31 for controlling the temperature of the hydrolysis catalytic converter 17 can be connected in an electrically conductive manner to a corresponding power supply by means of corresponding first heat conductor terminals 41. This correspondingly applies to the means 4 for heating the metering line 2, which means 4 can be provided with a corresponding power supply by means of corresponding second heat conductor terminals 42. The hydrolysis catalytic converter 17 has a second temperature measuring sensor 43 which can be connected by means of a corresponding second connecting element 44 to a control unit (not shown) . The temperature within or on the hydrolysis catalytic converter 17 can be determined by means of the second temperature measuring sensor 43. In operation, an aqueous urea solution 45 is delivered into the metering line 2 . The means 4 for heating the metering line 2 serve to heat the metering line 2 and thereby evaporate said aqueous urea solution and, if appropriate, depending on the temperature control, an at least partial thermolysis of the contained urea takes place to form ammonia. The corresponding gaseous substance mixture is introduced through the dispensing opening 3 into the hydrolysis catalytic converter 17, in which hydrolysis, preferably substantially complete hydrolysis of the contained urea takes place to form ammonia. A corresponding reducing agent substance mixture 35 leaves the hydrolysis catalytic converter 17, which reducing agent substance mixture 35 can be introduced into an exhaust line 14 of the exhaust system of an internal combustion engine. A method is preferable here in which the temperatures of the evaporator unit 12 and/or of the hydrolysis catalytic converter 17 are monitored by means of the temperature measuring sensors 39, 43, and both components 12, 17 can be heated by the corresponding means 4, 31. Figure 10 schematically shows a device 1 for providing a gaseous substance mixture 35 comprising at least one reducing agent. Said device 1 comprises, sequentially, a delivery line 6, by means of which an aqueous solution is delivered from a reservoir (not shown) into an evaporator unit 12. The evaporator unit 12 is adjoined by a hydrolysis catalytic converter 17, and the latter is adjoined by a dosing line 21 for metering the corresponding substance mixture to an exhaust line 14 (not shown) or by a metering unit 46 for metering the reducing agent substance mixture to the exhaust line 14. The evaporator unit 12 has a third temperature measuring sensor 47. The temperature of or in the delivery line 6 can be measured with said third temperature measuring sensor 47. The dosing line 21 and/or the metering unit 46 optionally has a fourth temperature measuring sensor 48, with which the temperature of the dosing line 21 and/or of the metering unit 46 or the temperature in the dosing line 21 and/or in the metering unit 46 can be measured. The evaporator unit 12 has means 4 for heating the metering line 2 and/or means 27 for heating the evaporator chamber 24. The hydrolysis catalytic converter 17 can optionally, alternatively or in addition to the means 4, 27, have means 31 for controlling the temperature of the hydrolysis catalytic converter 17. Optionally, alternatively or in addition, the delivery line 6 has temperature control means 49, by means of which the temperature of the delivery line 6 can be controlled. Particularly possible, advantageous and inventive here are one or more Peltier elements. The dosing line 21 and/or the metering unit 4 6 have metering temperature control means 50, by means of which the temperature of the dosing line 21 and/or of the metering unit 46 can be controlled. The use of at least one Peltier element is also advantageous here. All of the formed temperature control means 4, 27, 31, 49, 50 and all of the formed temperature measuring sensors 39, 43, 47, 48 are connected to a control unit 51. Said control unit 51 carries out the regulation of the temperature in a regulating loop which comprises at least one means 4, 27, 31, 49, 50 for temperature control and at least one temperature measuring sensor 39, 43, 47, 48. The number of temperature measuring sensors 39, 43, 47, 48 is preferably greater than the number of means 4, 27, 31, 4 9, 50 for controlling the temperature of the components 6, 2, 24, 17, 21, 46. The control unit 51 is preferably connected to a controller of the internal combustion engine or is integrated therein. The data of the controller of the internal combustion engine and the operating parameters of the internal combustion engine can advantageously be incorporated in the control of the evaporation and/or of the delivery to the evaporator unit 12. Figure 11 schematically shows a detail of a device for providing a gaseous substance mixture. Formed in an exhaust line 14 upstream of an SCR catalytic converter 18 is a honeycomb body 52 with ducts which can be traversed by a fluid, which honeycomb body 52 is part of a corresponding mixing means 53. The honeycomb body 52 is designed such that it can be traversed by the exhaust gas at least partially at an angle with respect to the main flow direction of the exhaust gas. Here, the main flow direction 54 is indicated by a corresponding arrow in figure 11. In the present exemplary embodiment, the honeycomb body 52 is of conical design. The honeycomb body has in particular a relatively large cutout 55 which is free from ducts. The dosing line 21 as part of the metering unit 46 opens out into said cutout 55, through which dosing line 21 the reducing agent substance mixture 35 is introduced in operation. Figure 12 schematically shows an example of a metering unit 46 with a dosing line 21 for metering the reducing agent substance mixture into an exhaust line 14. Here, the dosing line 21 extends through the wall of the exhaust line 14 in a curved state. The dosing line 21 has perforations 56 in the region which projects into the exhaust line 14. Here, the curvature or the curved entry of the dosing line 21 into the exhaust line 14 is not strictly necessary; the dosing line 21 could equally well enter into the exhaust line 14 perpendicularly or straight. Additionally formed here is a guide plate 23 which leads to a further improved mixture of the reducing agent substance mixture with the exhaust gas 13 in the exhaust line 14. Figure 13 schematically shows an embodiment of the device 1 for treating the exhaust gas of an internal combustion engine (not illustrated). Here, the evaporator unit 12 and the hydrolysis catalytic converter 17 are formed in a first exhaust branch 58. A distribution of the exhaust gas between the first 58 and the second exhaust gas branches 59 is obtained using a means 60 for flow guidance. The SCR catalytic converter 18 is formed downstream of the opening-out point 61 of the first exhaust branch 58 into the second exhaust branch 59. The evaporator unit 12 preferably has means 64 for depositing droplets, which means 64 can for example be formed within the metering line 2 or in or downstream of the second opening 26 of the evaporator chamber 24. Figure 14 shows an exemplary embodiment of a means 64 of said type for depositing droplets. Said means 64 is connected to the metering line 2 or generally to a line 65 through which vapour passes. Should droplets still be present in the vapour, these are deposited in the present example by the action of inertia. Formed in the means 64 are one or more impact plates 66 which force the flow to undergo deflections 67. The impact plate 66 and/or the housing 68 of the means 64 are heated, so that deposited droplets are likewise evaporated. Instead of the means 64 for depositing droplets shown here, it is also possible to alternatively or cumulatively take other measures; for example, the metering line 2 or the line 65 can, in regions, have narrowed cross sections, projections, deflections or the like. Figure 15 schematically shows a further exemplary embodiment of an evaporator unit 12, in which a metering line 2 can be heated by means 4 for heating the metering line 2. Here, the means 4 for heating the metering line 2 comprise a bar-shaped heating element 69 which can be connected by means of electrical terminals 70 to a power source. Formed in the metering line 2 is a means 64 for depositing droplets which can be heated by means of the contact with the bar-shaped heating element 69. Figure 16 schematically shows a further exemplary embodiment of an evaporator unit 12 in which the metering line 2 is wound, in the form of a loop, twice around the bar-shaped heating element 69. Figures 17 and 18 show exemplary embodiments of evaporator units 12 in which the metering line 2 is not wound around the longitudinal axis of the bar-shaped heating element 69 but is fastened in loops to the bar-shaped heating element 69. Fundamentally preferred is a materially-joined connection between the metering line 2 and the bar-shaped heating element 69, in particular a brazed connection. Figures 19 and 20 schematically show a further exemplary embodiment of a device 1 for providing a gaseous substance mixture comprising at least one of the following substances: a) a reducing agent, preferably ammonia, and b) at least one reducing agent precursor, in particular urea, having a hydrolysis catalytic converter 17. The device 1 comprises at least one metering line 2, in the present exemplary embodiment four metering lines 2, which are wound in spiral fashion around a bar-shaped heating element 69. Each of the metering lines 2 has in each case one dispensing opening 3, through which, in operation, a gaseous substance mixture which comprises a reducing agent is dispensed. The dispensing openings 3 are in each case distributed so as to be distributed substantially uniformly on a circle. The metering lines 2 are connected to a reservoir 20 (not shown here) from which an aqueous solution 45 of at least one reducing agent precursor is delivered into the metering line 2 by a delivery means 19. The metering lines 2 and the heating element 69 are part of a corresponding reducing agent solution evaporator 16. Formed downstream of the dispensing openings 3 is a hydrolysis catalytic converter 17 which can likewise be heated by a bar-shaped heating element 69. In one advantageous refinement, only one bar-shaped heating element 69 is formed, which heating element 69 is in thermal contact both with the metering line(s) 2 and with the hydrolysis catalytic converter 17. In the present exemplary embodiment, the hydrolysis catalytic converter 17 is embodied as an annular honeycomb body. The hydrolysis catalytic converter 17 is adjoined downstream by a dosing line 21, via which, in operation, the gas flow comprising at least one reducing agent can be introduced into the exhaust line 14. A mechanical connection to the exhaust line 14 can be produced by the connecting means 71. Also formed is thermal insulation 72, by means of which the hydrolysis catalytic converter 17 is thermally decoupled from the exhaust line 14. Also formed is a heat shield 73, by means of which the hydrolysis catalytic converter 17 is protected from a radiation of heat. Furthermore, air gap insulation 74, which likewise serves as thermal insulation, is formed between an outer housing 75 and an inner housing 76. Figure 20 shows a cross section through that region of the metering lines 2 which can be seen encircling the bar-shaped heating element 69. Figure 21 schematically shows a further exemplary embodiment of a device 15 for treating exhaust gas 13. In contrast to the embodiment in figure 4, a valve 77 is formed in the delivery line 6, which valve 77 serves for dosing the aqueous solution 45 into the evaporator unit 12. The valve 77 can be actuated by means of a control terminal 78. Figure 22 schematically shows an opening-out region 79 of a metering unit 46 into the exhaust line 14, Here, the exhaust line 14 and/or the metering unit has an aperture 80 which, in operation, produces a dead zone or calming zone of the exhaust gas flow, and consequently a region of reduced pressure, in the opening-out region 79, and thereby ensures that no exhaust gas is pressed into the dosing unit 46. The dosing unit 46 also has a temperature sensor 81 which comprises an annular thermoresistor. Should depositions form in said region, then the temperature sensor 81 can be connected to a power source (not shown) in order to thereby bring about a temperature increase to a second nominal temperature, for example of 550°C or more or even of 600 °C and more, and cause a dissolution or reduction of the depositions. Figure 23 schematically shows a cross section through a honeycomb body 82 which can be used both as a hydrolysis catalytic converter 17 and also as an SCR catalytic converter 18, with it being necessary here for other catalytically active coatings to be applied. The honeycomb body 82 is constructed from smooth metallic layers 83 and corrugated metallic layers 84 which, in this exemplary embodiment, are layered to form three stacks and are then wound with one another. The honeycomb body 82 also comprises a casing tube 85 which closes off the honeycomb body 82 to the outside. Smooth 83 and corrugated layers 84 form ducts 86 which can be traversed by exhaust gas 13. Figure 24 shows a further example of a honeycomb body 87 which is of annular design and can be used both as a hydrolysis catalytic converter 17 and also as an SCR catalytic converter 18, with it being necessary here for other catalytically active coatings to be applied. The honeycomb body 87 is constructed from layers 88 which have smooth 89 and corrugated sections 90 which are folded onto one another and form ducts 8 6 which can be traversed by exhaust gas 13. The honeycomb body 87 is closed off by means of an outer casing tube 91 and an inner casing tube 92. In the case in particular of a metering line 2 which is heated by means 4, 69, it is fundamentally advantageous to provide heating from the other side in addition to single-sided heating. It is for example possible for further sleeve-shaped heating elements to be formed which enclose the metering line from the outside. It is fundamentally advantageous if, at a certain cross section of the metering line 2 the temperature over the periphery differs from a mean temperature at most by +25°C or -25°C in operation. The hydrolysis catalytic converter 17 is fundamentally also a tube which is provided with a coating which catalyses the hydrolysis in particular of urea to form ammonia, or else a casing tube having at least one structured metallic layer which is applied to the outer periphery and which preferably has a freely traversable cross section radially in its interior which is at least 20% of the entire cross section of the casing tube. Said embodiments are preferably heated from the outside. Before starting the provision of reducing agent upstream of the SCR catalytic converter 18, the process is preferably fundamentally as follows: it is initially checked as to whether a current supply or fuel supply is ensured for the present temperature control and/or heating means 4, 27, 31, 49, 50, 63, 69; if it is determined that the current and/or fuel supply is ensured, then the evaporator unit 12 and if appropriate the hydrolysis catalytic converter 17 are heated in each case to a predetermined nominal temperature, in particular a metering line 2 is heated to approximately 350 to 450°C and/or an evaporator chamber 24 is heated to approximately 350 to 450°C, preferably in each case approximately 380°C; aqueous solution 45 is delivered in parallel to the evaporator chamber 24, in particular to the connecting unit 11, with it being possible on the one hand for a volume of aqueous solution 45 to be delivered which substantially corresponds to the volume of the delivery line 6, and on the other hand for a corresponding sensor, which operates for example on the basis of conductivity measurements, to be formed at a corresponding point, for example on, in or adjacent to the connecting unit 11; the temperature of the SCR catalytic converter 18 or of the exhaust line 14 is then determined, in particular measured and/or calculated from the data of an engine controller. If the temperature of the SCR catalytic converter 18 is above a predefinable limit value, in particular the "light-off" temperature of the SCR catalytic converter 18, the evaporator unit 12 is supplied with the aqueous solution 45. If the evaporator unit 12, the metering line 2 and/or the evaporator chamber 24 are still substantially at their operating temperature, then the above-specified diagnosis steps can be omitted. In operation, the heating power imparted to the evaporator unit 12 correlates with the delivery quantity of aqueous solution 45. This means in particular that it is checked as to what level of nominal heating power is required for the evaporation of the respective delivery quantity. If the measured actual heating power for a timespan is below the nominal heating power, then a warning is output to the user, since a reduction of the cross section of the metering line 2 and/or of the dosing line 21 could then be present. It is also advantageous, at regular, predefinable time intervals, to heat the evaporator unit 12, the metering line 2, the evaporator chamber 24, the hydrolysis catalytic converter 17, the dosing line 21 and/or the metering unit 4 6 to a temperature which is above the normal operating temperature, in order to thereby dissolve any depositions which may be present. When the evaporation is ended, which occurs for example when the internal combustion engine is switched off, the aqueous solution 45 can be returned from the metering line 2. Before the return delivery from the metering line 2, the delivery of aqueous solution 45 is preferably firstly suspended, with the evaporator unit 12, the metering line 2 and/or the evaporator chamber 24 however still being heated to the usual temperature in order to thereby carry out complete evaporation and to thereby prevent any impurities present in the evaporator unit 12, the metering line 2 and/or the evaporator chamber 24 from passing into the delivery line 6 during the return delivery. After a certain time has elapsed, the return delivery can be initiated by the delivery means 19. A valve is advantageously formed on or adjacent to the connecting unit 11, by means of which valve air can be sucked in during the return delivery. The return delivery fundamentally takes place until the delivery line 6 is substantially emptied into the reservoir 20. In the event of intense changes in the delivery quantity of the aqueous solution 45 which is to be delivered, which can for example be attributed to a sharply-rising concentration of nitrogen oxides in the exhaust gas of the internal combustion engine, situations can occur in which the evaporator unit 12 is not capable of immediately evaporating a considerably higher quantity of aqueous solution 45, since the correspondingly increased heating cannot take place so quickly. In this case, it is preferable to increase the delivery quantity of aqueous solution 45 only to such an extent that complete evaporation is still possible. The quantity of reducing agent to be dispensed, and consequently also the quantity of aqueous solution 45 which is to be evaporated, can be determined as a function for example of at least one of the following conditions: a) the nitrogen oxide concentration in the exhaust gas; b) a forecast nitrogen oxide generation which preferably occurs when the exhaust gas passes the SCR catalytic converter 18; c) the maximum quantity of reducing agent which can be converted directly by the SCR catalytic converter 18. The reservoir 20, the delivery line 6, the evaporator unit 12, the metering line 2, the evaporator chamber 24 and/or the hydrolysis catalytic converter 17 can be formed to be in thermal contact for example with the fuel tank of the internal combustion engine. For frost protection reasons, said fuel tank usually has a heater, which can then also provide frost protection for the above-specified components. According to a further advantageous aspect, a device 1 is proposed for providing a gaseous substance mixture comprising at least one of the following substances: a) at least one reducing agent and b) at least one reducing agent precursor. Here, the device 1 comprises a reservoir 20 for an aqueous solution 45 comprising at least one reducing agent precursor. The aqueous solution 45 can be delivered from the reservoir 20 into at least one metering line 2 with a dispensing opening 3 by a delivery means 19. Means 4 for heating the metering line 2 are advantageously formed, by means of which the at least one metering line 2 can be heated above a critical temperature which is greater than the boiling temperature of water. Said temperature is preferably 350 °C or more, preferably 400°C or more, in particular approximately 380°C. One advantageous refinement of said device 1 provides that the delivery means 19 comprises at least one pump. The latter is preferably a dosing pump. According to a further advantageous refinement of this device, a valve for dosing the quantity of aqueous solution 45 is formed between the delivery means 19 and the metering line 2. The means 4 for heating also advantageously comprise at least one of the following elements: a) an electrical resistor heater; b) heat transfer means for utilizing the waste heat of at least one other component; c) at least one Peltier element and d) a means for burning a fuel. A further advantageous embodiment of said device is characterized in that the device 1 is designed such that, in operation, the temperature across the length of the metering line 2 is at most 25°C above and below a mean temperature. A further advantageous embodiment of said device is characterized in that the metering line 2 has a traversable cross section of at most 20 mm2. It is also advantageous if the metering line 2 is formed from a material comprising at least one of the following materials: a) copper; b) aluminium; c) a nickel-based material; d) chrome-nickel steel and e) noble steel. The metering line 2 has in particular a length of from 0.1 to 5 m, preferably a length of from 0.3 to 0.7 m, particularly preferably substantially 0.5 m. The metering line 2 preferably has a wall thickness of 0.1 to 0.5 mm. The metering line 2 preferably has a heat capacity of at least 150 J/K (Joule per Kelvin). According to a further advantageous embodiment of said device 1, the metering line 2 and the means 4 for heating the metering line 2 have, at least in at least one partial region, at least one of the following arrangements relative to one another: a) the metering line 2 and the means 4 for heating the metering line 2 are formed coaxially with respect to one another at least in a partial region; b) the metering line 2 and the means 4 for heating the metering line 2 are formed concentrically with respect to one another at least in a partial region; c) the metering line 2 and the means 4 for heating the metering line 2 are formed adjacent to one another at least in a partial region; d) the metering line 2 is formed at least in a partial region so as to be wound around the means 4 for heating the metering line 2; e) the means 4 for heating the metering line 2 constitutes, at least in partial regions, a bar-shaped heating element 69, with the metering line 2 being formed so as to be wound around said bar-shaped heating element 69 and f) the metering line 2 forms a duct in a bar-shaped heating element 69. According to a further advantageous embodiment of the device 1, the metering line 2 and the means 4 for heating the metering line 2 are connected to one another in a materially joined fashion at least in partial regions. A materially joined connection is to be understood in particular as a soldered and/or welded connection. According to a further advantageous embodiment of the device 1, the metering line 2 is at least partially provided with a coating which catalyses the hydrolysis of a reducing agent precursor to form a reducing agent. The device 1 preferably comprises at least one measuring sensor 5 for determining the temperature of the metering line 2. Said measuring sensor can preferably be connected to a power source 5 in order to thereby permit, for example within the context of an emergency program, heating of the metering line 2 above the critical temperature. Also described is an advantageous method for providing a gaseous substance mixture comprising at least one of the following substances: a) at least one reducing agent, and b) at least one reducing agent precursor. Here, an aqueous solution 45 of at least one reducing agent precursor is delivered from a reservoir 20 into a metering line 2. Here, the metering line 2 is heated in such a way that the aqueous solution 45 is completely evaporated to form the gaseous substance mixture. Completely is to be understood here in particular to mean an evaporation in which 90% by weight and more of the aqueous solution, preferably 95% by weight and more, particularly preferably 98% by weight of the aqueous solution is evaporated. One advantageous refinement of said method is aimed at at least one of the reducing agent precursors a) urea and b) ammonium formate being comprised in at least one of the following components: A) the substance mixture and B) the aqueous solution. It is also advantageous for the temperatures in the metering line 2 to be at a mean temperature between 380°C and 450°C. The temperature along a length of the metering line 2 is preferably at most 25 °C above or below a mean temperature, preferably a mean temperature of 380°C to 450°C. According to a further advantageous embodiment of said method, a heating power which varies by up to 500 W/s is used during the heating process. A quantity of 0.5 ml/s of the aqueous solution 45 is preferably delivered into the metering line 2. It is also preferable for the metering line 2 to have a traversable cross section of at most 20 mm2. The metering line 2 is preferably heated to a second temperature which is higher than the critical temperature at which complete evaporation of the aqueous solution 45 takes place, in order to thereby dissolve if appropriate any depositions which may be present. According to a further advantageous embodiment of said method, the temperature of the metering line 2 is determined before the start of the evaporation, and is aligned with other known temperatures. Here, these can for example be other known or measured temperatures in the automobile, such as for example the ambient temperature measured by means of an external temperature sensor, or the cooling water temperature. According to a further advantageous embodiment of said method, the heating of the metering line 2 is carried out by means of an electrical resistance heater, with the resistance of said resistance heater being determined before the start of heating and the heating of the metering line taking place as a function of the determined resistance. A further advantageous refinement of said method is aimed at the introduced heating power during the heating of the metering line 2 being monitored. According to a further advantageous embodiment of said method, the heating is interrupted if, over a predefinable timespan, the heating power remains below a value which is dependent on the quantity of aqueous solution to be evaporated. According to a further advantageous present aspect, a device 1 is described for providing a gaseous substance mixture comprising at least one of the following substances: a) at least one reducing agent and b) at least one reducing agent precursor. Here, a reservoir 20 for an aqueous solution 45 comprising at least one reducing agent precursor is formed, which reservoir 20 can be flow-connected to an evaporator chamber 24. Furthermore, a means for dosing the aqueous solution 45 is formed in the evaporator chamber 24, with means 27, 63 for heating the evaporator chamber 24 being formed, with which means 27, 63 the evaporator chamber 24 can be heated to a temperature greater than or equal to a critical temperature at which the aqueous solution is at least partially evaporated. According to one advantageous refinement of said device 1, the means for dosing the aqueous solution 45 comprise at least one nozzle 62. The evaporator chamber 24 advantageously has a substantially closed volume which has only a first opening 25 for connecting a delivery line 6 for the aqueous solution 45, and a second opening 26 for connecting a metering line 2 for discharging the gaseous substance mixture. According to one advantageous refinement of said device 1, the evaporator chamber 24 encompasses a substantially closed volume which has only a first opening 25 for connecting a delivery line 6 for the aqueous solution, a second opening 26 for connecting a metering line 2 for discharging the gaseous substance mixture, and a third opening 36 for metering exhaust gas 14. A further advantageous refinement of said device provides that means 27, 63 for heating the evaporator chamber 24 comprise at least one of the following components: a) an electrical resistance heater 27 and b) a means 63 for burning a fuel. It is also advantageous that the evaporator chamber 24 is substantially spherically symmetrical. Here, the evaporator chamber 24 preferably has a radius of 2 mm to 25 mm. It is also advantageous for the evaporator chamber 24 to have a volume of 30 to 4000 mm3. The means 27, 63 for heating the evaporator chamber can impart a heating power of up to 5 kW. A delivery line 6 for delivering the aqueous solution 45 is also advantageously formed, which delivery line 6 connects the evaporator chamber 24 to a reservoir 20 and in which a delivery means 19 is formed, by means of which a fluid can be delivered through the delivery line 6. According to a further advantageous embodiment of said device, the latter is designed such that, in operation, the temperature of the evaporator chamber 24 is at most 25 °C above and below a mean temperature. It is also advantageous for the evaporator chamber 24 to have, at least in partial regions, means 28 for increasing the wetting capacity of the surface. Said means 28 can in particular comprise a structuring of the inner surface (projections or the like) of the evaporator chamber 24. Also described is a method for providing a gaseous substance mixture comprising at least one of the following substances: a) at least one reducing agent and b) at least one reducing agent precursor. An aqueous solution 45 of at least one reducing agent precursor is delivered into an evaporator chamber 24, with the evaporator chamber 24 being heated in such a way that the aqueous solution 45 is completely evaporated to form the gaseous substance mixture. Said method can advantageously be further developed in that the evaporator chamber 24 comprises a substantially closed volume which has only a first opening 25 for connecting a delivery line 6 for the aqueous solution 45, and a second opening 26 for connecting a metering line 2 for discharging the gaseous substance mixture. Alternatively, the evaporator chamber 24 can encompass a substantially closed volume which has only a first opening 25 for connecting a delivery line 6 for the aqueous solution 45, a second opening 26 for connecting a metering line 2 for discharging the gaseous substance mixture, and a third opening 36 for metering exhaust gas 14. Said methods can advantageously be further developed in that the heating is regulated. The evaporator chamber 24 is in particular heated to a mean temperature of 350 to 450 'C. It is also advantageous for the evaporator chamber 24 to be heated to a mean temperature in such a way that the temperature does not at any point of the evaporator chamber 2 4 deviate from a mean temperature by more than +25°C or -25°C. The device 15 according to the invention advantageously permits the provision of a sufficiently large quantity of reducing agent for the selective catalytic reduction of nitrogen oxides in the SCR catalytic converter 18, with it being possible at the same time for the hydrolysis catalytic converter 17 to be designed with a smaller volume than is known from the prior art, since the hydrolysis catalytic converter 17 here is not traversed by exhaust gas. List of rafaranca symbols 1 Device for providing a gaseous substance mixture 2 Metering line 3 Dispensing opening 4 Means for heating the metering line 5 Measuring sensor 6 Delivery line 7 Means for temperature control 8 Peltier element 9 Cooling body 10 Electrical terminal 11 Connecting unit 12 Evaporator unit 13 Exhaust gas 14 Exhaust line 15 Device for treating the exhaust gas of an internal combustion engine 16 Reducing agent solution evaporator 17 Hydrolysis catalytic converter 18 SCR catalytic converter 19 Delivery means 20 Reservoir 21 Dosing line 22 Dosing opening 23 Mixing means 2 4 Evaporator chamber 25 First opening 2 6 Second opening 27 Means for heating the evaporator chamber 28 Structure 29 Casing of the evaporator unit 30 Heat conductor terminal 31 Means for temperature control of the hydrolysis catalytic converter 32 Casing of the hydrolysis catalytic converter 33 Connecting means 34 Conducting plate 35 Reducing agent substance mixture 36 Third opening 37 Guide structure 38 Heat conductor 39 First temperature measuring sensor 40 Connecting element 41 First heat conductor terminal 42 Second heat conductor terminal 43 Second temperature measuring sensor 44 Second connecting element 45 Aqueous solution 46 Metering unit 47 Third temperature measuring sensor 48 Fourth temperature measuring sensor 4 9 Temperature control means 50 Metering temperature control means 51 Control unit 52 Honeycomb body 53 Mixing means 54 Main flow direction 55 Cutout 56 Perforation 57 Length 58 First exhaust branch 59 Second exhaust branch 60 Means for flow guidance 61 Confluence 62 Nozzle 63 Means for burning hydrocarbons 64 Means for depositing droplets 65 Line 66 Impact plate 67 Deflection 68 Housing 69 Bar-shaped heating element 70 Electrical terminal 71 Connecting means 72 Thermal insulation 73 Heat shield 74 Air gap insulation 75 Outer housing 76 Inner housing 77 Valve 78 Control terminal 79 Opening-out region 8 0 Aperture 81 Temperature sensor 8 2 Honeycomb body 83 Smooth metallic layer 84 Corrugated metallic layer 85 Casing tube 8 6 Duct 8 7 Annular honeycomb body 88 Layer 8 9 Smooth region 90 Corrugated region 91 Outer casing tube 92 Inner casing tube We Claim: 1. Device (15) for treating the exhaust gas of an internal combustion engine, at least comprising: o a reducing agent solution evaporator (16), o a hydrolysis catalytic converter (17), which is connected to the reducing agent solution evaporator (16), for the hydrolysis of in particular urea to form ammonia, and o an SCR catalytic converter (18) for the selective catalytic reduction of nitrogen oxides, with the reducing agent solution evaporator (16) comprising an evaporator unit (12) for providing a gaseous substance mixture comprising at least one of the following substances: a. at least one reducing agent precursor, and b. a reducing agent with it being possible, by means of the evaporator unit (12), for an aqueous solution (45) comprising at least one reducing agent precursor to be evaporated, with the SCR catalytic converter (18) being formed in the exhaust line (14), characterized in that the reducing agent solution evaporator (16) and the hydrolysis catalytic converter (17) are formed outside the exhaust line (14) and such that they can be connected to the latter wherein thermal insulation (72) is formed downstream of the hydrolysis catalytic converter (17), the thermal insulation (72) prevents that the hydrolysis catalytic converter (17) dissipated heat to the exhaust line (14). 2. Device as claimed in Claim 1, in which the evaporator unit (12) is connected to a reservoir (20) for the aqueous solution (45) by a delivery line (6), wherein delivery line (6) and evaporator unit (12) are connected by a connecting unit (11). 3. Device as claimed in Claim 2, in which the connecting unit (11) is formed at least in part of a material having a thermal conductivity than 10 W/m K (Watts per Meter and Kelvin). 4. Device as claimed in claim 2 or 3, in which the connecting unit (11) is formed of at least one substance comprising at least one of the following materials: a. a ceramic substance and b. Polytetrafluoroethylene (PTFE) 5. Device as claimed in claim 2 or3, in which the connecting unit (11) is designed such that a temperature gradient of 40 K/mm (Kelvin per millimetre) and greater can be maintained over a length of the connecting unit (11). 6. Device as claimed in one of the claims 1 to 3, in which at least one of the following components has a coating which catalyses the hydrolysis of urea: a. at least parts of the connecting unit (11); b. at least parts of a metering line (2) for metering the gaseous substance mixture to the hydrolysis catalytic converter (17); c. at least parts of the evaporator unit (12); d. at least parts of a dosing line (21) for metering the generated reducing agent to the exhaust system and e. at least parts of a metering unit (46), by means of which the hydrolysis catalytic converter (17) can be connected to the exhaust line (14). 7. Device as claimed in Claim 1, in which the thermal insulation (72) is formed directly adjoining the hydrolysis catalyt~cc onverter (17). 8. Method for treating the exhaust gas of an internal combustion engine, comprising the following steps: a. providing a gaseous substance mixture comprising at least one of the following substances: al) reducing agent and a2) at least one reducing agent precursor; b. hydrolysis of the at least one reducing agent precursor in a hydrolysis catalytic converter (17), with a reducing agent substance mixture (35) being obtained; c. subjecting an SCR catalytic converter (18) to the reducing agent substance mixture (35) and the exhaust gas (14) for the at least partial selective catalytic reduction of nitrogen oxides (NO,) contained in the exhaust gas, with a mixture of the reducing agent substance mixture (35) with at least parts of the exhaust gas (14) taking place after step b) wherein thermal contact of hydrolysis catalystic converter (17) and exhaust gas (13) is inhibited by means of a thermal insulator (72) disposed downstream the hydrolysis catalystic converter (17). 9. Method as claimed in Claim 8 , in which step a) comprises an evaporation, in an evaporator unit (12), of an aqueous solution (45) comprising at least one reducing agent precursor. 10. Method as claimed in Claim 8 or 9, in which the temperature of at least one of the following components is regulated: a) at least parts of the evaporator unit (12); b) the hydrolysis catalytic converter (17); c) a delivery line (6) for delivering the aqueous solution (45) to the evaporator unit (12); d) a metering line (2) for metering the gaseous substance mixture to the hydrolysis catalytic converter (17); e) a dosing line (21) for metering the generated reducing agent to the exhaust system and f) a metering unit (46), by means of which the hydrolysis catalytic converter (17) can be flow-connected to an exhaust line (14) of the internal combustion engine.

Documents:

8717-delnp-2008-Abstract-(26-07-2013).pdf

8717-delnp-2008-abstract.pdf

8717-delnp-2008-Claims-(26-07-2013).pdf

8717-delnp-2008-claims.pdf

8717-delnp-2008-Correspondence Others-(11-04-2013).pdf

8717-delnp-2008-Correspondence-Others-(26-07-2013).pdf

8717-delnp-2008-correspondence-others.pdf

8717-delnp-2008-description (complete).pdf

8717-delnp-2008-Drawings-(26-07-2013).pdf

8717-delnp-2008-drawings.pdf

8717-delnp-2008-form-1.pdf

8717-delnp-2008-Form-13-(26-07-2013).pdf

8717-delnp-2008-form-18.pdf

8717-delnp-2008-form-2.pdf

8717-delnp-2008-Form-3-(11-04-2013).pdf

8717-delnp-2008-form-3.pdf

8717-delnp-2008-form-5.pdf

8717-delnp-2008-GPA-(26-07-2013).pdf

8717-delnp-2008-pct-210.pdf

8717-delnp-2008-pct-304.pdf

8717-delnp-2008-Petition-137-(26-07-2013).pdf

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