Title of Invention

A CATALYST USEFUL FOR THE DECOMPOSITION OF NITROUS OXIDE TO NITROGEN AND OXYGEN

Abstract

The present invention provides a catalyst for the decomposition of nitrous oxide to nitrogen and oxygen at low temperature. More particularly, the present invention provides an alkali metal promoted bulk metal oxide with bulk metal oxide to alkali weight ratio ranging between 1:0 to 1:0.2 wherein the said metal oxide is selected from the oxides of cobalt, nickel, copper and iron. The said catalyst is active at different environmental conditions of oxygen, steam or a mixture thereof, for the decomposition of nitrous oxide to nitrogen and oxygen.

Full Text

Field of the invention The present invention relates to a catalyst for the decomposition of nitrous oxide to nitrogen and oxygen at low temperature. Particularly, the present invention relates to bulk metal oxide as a catalyst for the decomposing nitrous oxide to nitrogen and oxygen. More particularly, the present invention relates to an alkali metal promoted bulk metal oxide acting as a catalyst for the decomposing nitrous oxide to nitrogen and oxygen. The present invention also relates to a process for the preparation of an alkali metal promoted bulk metal oxide for the decomposition of nitrous oxide to nitrogen and oxygen. Background of the Invention Nitrous oxide has been identified as a contributor to the destruction of ozone in the stratosphere. It is recognized as a potential green house gas as its global warming capacity is as high as about 300 times that of carbon dioxide. The reduction of nitrous oxide levels is being studied extensively and several methods have been proposed. One promising method of converting nitrous oxide is its decomposition into the elements of nitrogen and oxygen with the aid of a catalyst. U. S. Pat. No 6,890,499 describes about the catalyst for decomposing nitrous oxide using a mixed catalyst composed of cobalt and magnesium oxides. About 55% decomposition of N2O was achieved at 300 °C. At 400 °C >99% of the N2O entering into the reactor was decomposed to give N2 and O2. US patent 6,846,471 discloses a catalyst system for decomposing nitrous oxide. The catalyst comprising a support having an active component such as aluminium, magnesium and rhodium. The disclosed catalyst can decompose N20 at a reaction temperature of around 350-400 °C. US patent 6,429,168 claims a process for the conversion of nitrous oxide to nitrogen and oxygen using a supported catalyst comprising iron and optionally other metals and a novel catalyst composition. These catalysts are active at high temperatures usually around 650 °C. DE-A-19700490 claims a nitrous oxide decomposition catalyst, which is composed of a mixture of Co3O4 and La1-x Cux C0O3 and which, in pure form, achieves complete N2O decomposition (starting from 2000 ppm of N2 0 in synthetic air) at a temperature as low as about 300 °C. The introduction of this active component into a ceramic matrix, not specified in full detail, with 25% by weight of the active component shifts the reaction temperature for complete N2O decomposition to about 600 °C. US Pat. No. 5,705,136 describes a process for decomposing nitrogen oxides based on catalysts compring mixed oxides of MgO and CoO solid solutions. By virtue of the nature of the preparation process, the manner of fixing the cobalt atoms to the MgO support or incorporating them into the same cobalt exists almost exclusively in the divalent state. The preferred active range for these catalysts is from 500 to 700 °C. However, there remain certain problems as per the process for decomposition of nitrous oxide using catalysts described above. When moisture is present in the reaction gas, the catalysts show decrease in the activity. This remains as a major problem to be solved. Most of the catalyst systems disclosed need high reaction temperature in order to achieve more than 99% decomposition of N2O. The main objective of the present invention is to provide a catalyst for decomposing nitrous oxide at low temperatures, which is also active, even the N2O stream contains moisture. Objectives of the invention The main objective of the present invention is to provide a catalyst for the decomposing nitrous oxide at low temperatures. Another objective of the present invention is to provide alkali metal promoted bulk metal oxide useful for the decomposition of nitrous oxide at lower temperatures. Another objective of the present invention is to provide a suitable precipitating agent for making bulk metal oxide. Another objective is to provide a suitable alkali metal and its composition with bulk metal oxide to obtain the nitrous oxide decomposition >99%. Yet another object is to provide a suitable catalyst for the nitrous oxide decomposition even in the presence of oxygen and moisture. Yet another object is to provide a suitable catalyst, which is active for the decomposition of nitrous oxide, under different environmental conditions of stream, oxygen and mixture thereof. Summary of the invention Accordingly the present invention provides a catalyst useful for the decomposition of nitrous oxide comprising an alkali metal promoted bulk metal oxide with bulk metal oxide to alkali weight ratio ranging between 1:0 to 1:0.2 wherein the said metal oxide is selected from the oxides of cobalt, nickel, copper and iron. In an embodiment of the present invention the alkali metal used is selected from the group consisting of Sodium, Potassium and Cesium. In yet another embodiment the bulk metal oxide used is preferably cobalt oxide (CO3O4). In yet another embodiment the preferable composition of the catalyst is 0.05 -0.1 wt%Cs/CO3O4 In yet another embodiment the catalyst is active for the decomposition of nitrous oxide into nitrogen and oxygen under different environment conditions of oxygen, steam and mixture thereof, at a temperature in the range of 250 to 350°C. In yet another embodiment the catalyst with composition 0.05%Cs/CO3O4 decomposes 100% nitrous oxide to nitrogen and oxygen, at a temperature of 275 °C under oxygen atmosphere. In yet another embodiment the catalyst with composition 0.05% Cs/CO3O4 decomposes 100% nitrous oxide to nitrogen and oxygen, at a temperature of 325 °C under steam (H2O) atmosphere. In yet another embodiment the catalyst with composition 0.05%Cs/CO3O4 decomposes 100% nitrous oxide to nitrogen, at a temperature of 350 °C, under a mixture of oxygen and steam (H2O) atmosphere. The present invention further provides a process for the preparation of a catalyst useful for the decomposition of nitrous oxide which comprises precipitating the metal nitrate solution with a solution of a precipitating agent selected from sodium carbonate, ammonium carbonate and oxalic acid, at a temperature in the range of 25 to 30°C, washing the resultant precipitate with water and drying it at a temperature of 100 to 110°C for a period of 20 to30 hrs, followed by calcination at a temperature of 300 to 500°C for a period of 3 to 5 hrs to obtain the bulk metal oxide, impregnating the resultant bulk metal oxide with an aqueous solution of alkali metal nitrate, followed by drying at a temperature of 110 to 130°C and calcining the resultant product, at a temperature of 400 to 550°C to obtain the desired alkali metal promoted bulk metal oxide catalyst. In yet another embodiment the metal nitrate used is selected from the group consisting of nitrates of cobalt, nickel, copper and iron. In yet another embodiment the metal nitrate used is preferably cobalt nitrate. In yet another embodiment the alkali metal used is selected from sodium, potassium and cesium. In yet another embodiment the alkali metal used is preferably cesium. In yet another embodiment the weight % of alkali metal present in the catalyst is ranging between 1:0 to 1:0.2. In yet another embodiment the catalyst obtained has a preferable composition of 0.05-0.1 %Cs/CO3O4 In yet another embodiment the catalyst with composition 0.05% Cs/CO3O4 decomposes 100% nitrous oxide to nitrogen and oxygen, at a temperature of 275 °C under oxygen atmosphere. In yet another embodiment the catalyst with composition 0.05% Cs/ CO3O4 decomposes 100% nitrous oxide to nitrogen and oxygen, at a temperature of 325°C, under steam atmosphere. In yet another embodiment the catalyst with composition 0.05% Cs/ CO3O4 decomposes 100% nitrous oxide to nitrogen and oxygen, at a temperature of 350°C under a mixture of oxygen and steam (H2O) atmosphere. Detail description of the invention The present invention provides an alkali promoted bulk cobalt oxide catalyst for the decomposition of nitrous oxide at moderate temperatures of 150 to 350 °C and at atmospheric pressure. One of the features of present invention is that the preparation of bulk cobalt oxide uses one of the precipitating agents such as ammonium carbonate, sodium carbonate or oxalic acid to get high purity and high surface area containing bulk cobalt oxide. Another feature of the present investigation is to promote the cobalt oxide with an alkali metal. Different alkali metals such as Na, K, Cs are used. The content of alkali metal and its composition is crucial in getting the high nitrous oxide decomposition activity. The type of alkali metal also plays an important role in getting high catalytic activity when nitrous oxide contains considerable amount of moisture. Yet other feature of the present invention is achieving near 100% decomposition of nitrous oxide to nitrogen and oxygen. The over all high conversion of nitrous oxide more than 99% is achieved by adding small amount of alkali metal at reaction temperatures as low as 200-250 °C. Yet another feature of the present invention is the activity and stability of the catalyst in the presence of oxygen and moisture content. This is achieved by tuning the required surface alkali metal ion. The presence of specific amount of alkali metal ion is crucial in obtaining the desired decomposition of nitrous oxide at very low temperatures. The present invention is described with reference to the following examples, which are explained by way of illustration only and should not be construed to limit the scope of the present invention. Methods for preparing bulk metal oxides and alkali metal promoted metal oxide catalysts Example 1 Bulk cobalt oxide was prepared by precipitating the cobalt nitrate at room temperature. Ammonium carbonate, sodium carbonate and oxalic acid were used as precipitating agents. For instance, 1 M solution of cobalt nitrate was mixed with 0.5 M of sodium carbonate at room temperature. The precipitate thus obtained was washed with distilled water and dried at 100 °C for 24 h and then calcined at 400 °C for 4 h. This catalyst was used for decomposition of nitrous oxide under different conditions. Example 2 The metal oxides prepared were modified by promoters. Different alkali metals were used as promoters. Bulk metal oxides prepared by precipitating with sodium carbonate were promoted with alkali metal ion. Alkali metals such as Na, K, Cs were used as promoters. Alkali metals were added to the bulk metal oxides by impregnatingthe latter with an aqueous solution of alkali metal nitrate, followed by drying at 120 °C. Finally these samples were calcined at 500 °C for 5 h in flowing air. The atomic ratio of alkali metal to bulk metal oxide was varied from 0 to 0.4. Example 3 The bulk metal oxides prepared as mentioned in example 1 were tested for nitrous oxide decomposition to nitrogen and oxygen. The direct decomposition of N2O was carried out in a fixed bed continuous flow reactor. The reaction gas N2O diluted with He gas was fed into the reactor where the catalyst was held between two quartz wool plugs with a GHSV in the range of 1000 to 10,000 h-1. The reaction was studied by varying the reaction temperature between 150 and 550 °C. Table 1. Conversion data during nitrous oxide decomposition over different bulk metal oxides (Table Removed) Example 4 The alkali metal promted metal oxide catalysts were tested for nitrous oxide decomposition to nitrogen and oxygen. The direct decomposition of N2O was carried out in a fixed bed continuous flow reactor. The reaction gas N2O diluted with He gas was fed into the reactor where the catalyst was held between two quartz wool plugs with a GHSV in the range of 1000 to 10,000 h-1. The reaction was studied by varying the reaction temperature between 150 and 500 °C. Table 2. Conversion data during nitrous oxide decomposition over different alkali metal promoted bulk metal oxides Catalyst Reaction Temperature (°C) (Table Removed) Example 5 The alkali metal promoted metal oxide catalysts were studied for nitrous oxide decomposition under different reaction atmospheres. The direct decomposition of N2O was carried out in presence oxygen and water. The reaction was studied by varying the reaction temperature from 150 to 450 °C. Table 3. Decomposition of nitrous oxide over different alkali promoted bulk metal oxides under different reaction environments at a reaction temperature of 350 °C. (Table Removed) Example 6 The bulk cobalt oxide was promoted with alkali metal. Alkali metals was added to bilk cobalt oxide prepared using sodium carbonate by impregnation with an aqueous solution of alkali metal nitrate followed by drying at 120 °C and calcined finally at 500 °C for 4 h in air flow. The alkali metal content was varied between 0 and 0.2. These catalysts were tested for nitrous oxide decomposition at different temperatures ranging from 150 to 450 °C under different reaction. Table 4. Conversion data during nitrous oxide decomposition over different alkali metal promoted bulk cobalt oxide catalysts. (Table Removed) Example 7 Cesium alkali metal promoted cobalt oxide catalysts are prepared and studied for N2O decomposition. Cs was added to bulk cobalt oxide, which was prepared using sodium carbonate by impregnation with an aqueous solution of cesium nitrate followed by drying at 120 °C and calcined finally at 500 °C for 4 h in air flow. The alkali metal content is varied from 0 to 0.2. These catalysts are tested for nitrous oxide decomposition at different temperatures ranging from 150 to 450 °C. Table 5. Conversion data during nitrous oxide decomposition over cesium promoted cobalt oxide with varying Cs content. Reaction Temperature (°C) Catalyst (Table Removed) Example 8 Cesium alkali metal promoted cobalt oxide catalysts were prepared and studied for N2O decomposition under different atmospheres. These catalysts were tested for nitrous oxide decomposition at different temperatures ranging from 150 to 450 °C under oxygen and steam atmospheres. Table 6. Conversion data during nitrous oxide decomposition over cesium promoted cobalt oxide catalysts under different reaction atmosphere. (Table Removed) claim: 1. A catalyst useful for the decomposition of nitrous oxide comprising an alkali metal promoted bulk metal oxide with bulk metal oxide to alkali weight ratio ranging between 1:0 to 1:0.2 wherein the said metal oxide is selected from the oxides of cobalt, nickel, copper and iron. 2. A catalyst as claimed in claim 1, wherein the alkali metal used is selected from the group consisting of Sodium, Potassium and Cesium. 3. A catalyst as claimed in claim 1, wherein the bulk metal oxide used is preferably cobalt oxide (CO3O4). 4. A catalyst as claimed in claim 1, wherein the preferable composition of the catalyst is 0.05 - 0.1 wt % Cs/CO3O4 5. A catalyst as claimed in claim 1 is active for the decomposition of nitrous oxide into nitrogen and oxygen under different environment conditions of oxygen, steam and mixture thereof, at a temperature in the range of 250 -350 °C. 6. A catalyst as claimed in claim 1, wherein the catalyst with composition 0.05%Cs/CO3O4 decomposes 100% nitrous oxide to nitrogen and oxygen, at a temperature of 275 °C under oxygen atmosphere. 7. A catalyst as claimed in claim 1, wherein the catalyst with composition 0.05% Cs/CO3O4 decomposes 100% nitrous oxide to nitrogen and oxygen, at a temperature of 325 °C under steam (H2O) atmosphere. 8. A catalyst as claimed in claim 1, wherein the catalyst with composition 0.05%Cs/CO3O4 decomposes 100% nitrous oxide to nitrogen, at a temperature of 350 °C, under a mixture of oxygen and steam (H2O) atmosphere. 9. A process for the preparation of a catalyst useful for the decomposition of nitrous oxide which comprises precipitating the metal nitrate solution with a solution of a precipitating agent selected from sodium carbonate, ammonium carbonate and oxalic acid, at a temperature in the range of 25 to 30°C, washing the resultant precipitate with water and drying it at a temperature of 100 to 110°C for a period of 20 to30 hrs, followed by calcination at a temperature of 300 to 500°C for a period of 3 to 5 hrs to obtain the bulk metal oxide, impregnating the resultant bulk metal oxide with an aqueous solution of alkali metal nitrate, followed by drying at a temperature of 110 to 130°C and calcining the resultant product, at a temperature of 400 to 550°C to obtain the desired alkali metal promoted bulk metal oxide catalyst. 10. A process as claimed in claim 9, wherein the metal nitrate used is selected from the group consisting of nitrates of cobalt, nickel, copper and iron. 11. A process as claimed in claim 9, wherein the metal nitrate used is preferably cobalt nitrate. 12. A process as claimed in claim 9, wherein the alkali metal used is selected from sodium, potassium and cesium. 13. A process as claimed in claim 9, wherein the alkali metal used is preferably cesium. 14. A process as claimed in claim 9, wherein the weight % of alkali metal present in the catalyst is ranging between 1:0 to 1:0.2. 15. A process as claimed in claim 9, wherein the catalyst obtained has a preferable composition of 0.05 - 0.1 % Cs/ CO3O4 16. A process as claimed in claim 9, wherein the catalyst with composition 0.05% Cs/CO3O4 decomposes 100% nitrous oxide to nitrogen and oxygen, at a temperature of 275 °C under oxygen atmosphere. 17. A process for the preparation of a catalyst as claimed in claim 9, wherein the catalyst with composition 0.05% Cs/ CO3O4 decomposes 100% nitrous oxide to nitrogen and oxygen, at a temperature of 325°C, under steam atmosphere. 18. A process as claimed in claim 9, wherein the catalyst with composition 0.05% Cs/ CO3O4 decomposes 100% nitrous oxide to nitrogen and oxygen, at a temperature of 350°C under a mixture of oxygen and steam (H2O) atmosphere. 19. A catalyst useful for the decomposition of nitrous oxide and a process for the preparation thereof, substantially as herein described with reference to the examples.

Documents:

593-del-2007-abstract.pdf

593-del-2007-Claims-(12-12-2012).pdf

593-del-2007-claims.pdf

593-del-2007-Correspondence Others-(12-12-2012).pdf

593-del-2007-Correspondence Others-(26-08-2008).pdf

593-DEL-2007-Correspondence-Others.pdf

593-del-2007-Description (Complete)-(12-12-2012).pdf

593-del-2007-description (complete).pdf

593-del-2007-description (provisional).pdf

593-DEL-2007-Form-1.pdf

593-del-2007-Form-18-(26-08-2008).pdf

593-del-2007-form-18.pdf

593-DEL-2007-Form-2.pdf

593-del-2007-Form-3-(12-12-2012).pdf

593-DEL-2007-Form-3.pdf

593-DEL-2007-Form-5.pdf