|Title of Invention||
A METHOD OF MANUFACTURE OF SUPPORTED METAL CATALYSTS
|Abstract||A method of manufactrure of supported metal catalyf4 comprises the steps of exposing a shaped organic-inorganic nanocomposite material, such as herein described, to sunlight for 10--30 minutes until reduction takes place as indicated by the colour of the said material changing from colourless to bluei1 dipping the said nanocomposite material in a solution containing a support material and the active metal, stirring the same igorousJy, to re-o;.cidise the said composite; drying the said re-oxidised composite to obtain the supported metal cataJyst.|
|Full Text||This invention relates to a method of manufacture of supported meteil catalyste, that is, a method of reducing metaUio ions to zero vaLent state for preparing supported metal catalysts.
The invention can be made use of for the preparation of any supported metal catalysts, especially for preparation of noble metals supported on carbon for c^pHcadon as electrodes in fuel ceUs and other energy conversion devices, whidi is conventionally carried out using hydrogen or reducing agents such as HCHO, Sodium bisulphate.
Supported metal systems are prepared, according to the known art, by using metal ion precursors like hexachloroplatinic add (H^PtCle) for Pt, RUCI3 for Ru and after these ionic species are loaded on the support, tfie anchored or hooked up metal ions are reduced to the aero valent state by hydrogen at hi^ temperatures or by using suitable reducing events like HCHO, NjEjNHbOH Some of the limitations of the conventional methods are:
(i) In the hydrogen reduction method, usua% high temperatures have to be employed (around 600 K) and hence it leads to agglomesration of the metal particles. Normally the particle sizes obtained by hydrog^ reduction method are in the range of 10-20nm. If they were in the range 2-5nm, the value of
metal dispersions can be high and hence the activity of the resulting systems can be expected to be high.
(ii) When reducing agents like HCHO are employed, it's lower equilibrium limitation restricts the extent of reduction. This means that all the metal ion precursors could not be reduced to the metallic state and hence, the effective utilization of the loaded noble metal will be reduced.
The method proposed by this invention overcomes both these limitations, but also has certain other advantages like:
(i) the reducing agent could be easily removed from the medium, at the end of the preparation of the supported metal catalysts.
(ii) the material prepared by this method was used for making an electrode and the oxidation of methanol (relevant for use of anode for DMFC) was tested. The cyclic voltammogram obtained using electrodes prepared according to the method proposed herein is shown in Figl. The corresponding cyclic voltammogram of the electrode made without employing the method proposed herein is in Fig.2 and compm-ison was made with the material obtained by hydrogen reduction method shown in Fig 3 and given in Table 1. It is clear that the method according to this invention has certain definite advantages over the conventional methods such as reduction with hydrogen or with reducing agents like HCHO, NaHSOs.
The method of manufacture of supported metal catalysts, according to this invention, comprises the steps of esq^osing a shaped oiganic-inorganic nanocomposite material, such as herein described, to sunlight for 10-30 minutes untU reduction takes place as indicated by the colour of the said material changing from colourless to blue, dipping the said nanocomposite material in a solution containing a support material and the active metal, stirring the same vigorously, to reoxidise 4ie said composite; drying the said re-oxLdised composite to obtain the supported metal catalyst.
The preparation of the nanocomposite material has already been set out in the Complete Specification of our Application for Patent No. 117 CHE 2004 to which reference may be made.
This invention will now be described with reference to the accompanying drawings which illustrate, by way of example the cyclic voltammogram obtained using dectrodes prq)ared according to the method proposed herein (Flg.l) and the corresponding cydic voltammogram of the dectiode made without employing the method proposed herein (Fig.2), Comparison with the material obtained by hydrogen reduction method is shown in Fig 3 and given in Table 1. Fig.4 iUustrates the method steps.
EXAMPLE The nan0-composite material is shaped into form of a rod, sheet or fihn. In the Example, it is shaped mto the form a film F fixed to a glass slide S which is then exposed to sunlight for 30 minutes, when reduction takes place as can be seen from the fact that the colour of the film now changes from transparent to blue. It is then dipped in a solution B containing carbon (support material) and the active component hexachloroplatinic acid, while stirring the same vigorously, to reoxidise the said composite. The re-oxidised composite is then dried at 70 deg. Centigrade to obtain the support metal catalyst R, that is, Pt on C.
The terms and expressions herein are of description and not of limitation having regard to the scope and ambit of this invention.
|Indian Patent Application Number||548/CHE/2004|
|PG Journal Number||02/2008|
|Date of Filing||11-Jun-2004|
|Name of Patentee||M/S. INDIAN INSTITUTE OF TECHNOLOGY|
|Applicant Address||IIT P.O,CHENNAI 600 036,|
|PCT International Classification Number||B 22 F 1/00|
|PCT International Application Number||N/A|
|PCT International Filing date|