Catalytic Oxidation of CO and the Reduction of NO

These two processes were studied at Symyx using catalyst libraries of metal alloys of Rh, Pd, Pt, and Cu [168]. Triangular libraries (15 x 15 x 15) containing approximately 2-4 mg of 120 independently prepared catalysts were synthesized by deposition methods using fully automated radiofrequency sputtering techniques. Libraries with similar catalysts were also prepared by sol-gel-based methods.

The oxidation of CO was carried out in the presence of oxygen and the production of CO2 was determined by scanning mass spectroscopy. The amount of CO2 produced followed the trend Rh > Pd > Pt, which is in good agreement with results from experiments with single crystalline surfaces as well as supported catalysts.

In subsequent libraries, one of the noble metals was replaced by transition metals. In the case of a library with Rh/Pd/Cu, the 1:1 composition of Cu/Rh showed activity very similar to that of pure Rh and the catalyst with 93% Cu and 7% Rh maintains 40% of the activity of pure Rh. In addition, Pt/Cu and Pd/Cu binaries show activity enhancements over the respective pure metals, with the enhancement being stronger at low temperatures than at high temperatures.

The oxidation of CO by NO was investigated along the same lines using the above-mentioned Rh/Pd/Pt library. The reaction was carried out at ambient pressure at various temperatures. As in the CO oxidation by oxygen, the activity for the oxidation of CO by NO follows the trend Rh > Pd > Pt similar to that reported in the literature for bulk catalysts.

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