INFLUENCE OF METAL-PARTICLE SIZE AND EFFECT OF GOLD ADDITION ON THE ACTIVITY AND SELECTIVITY OF PT/AL2O3 CATALYSTS IN THE REDUCTION OF NITRIC-OXIDE BY METHANE

The catalytic reduction of nitric oxide by methane over alumina supported platinum and Pt Au catalysts was investigated using a gas mixture of 2 vol.-% NO and CH4 in helium at 250-350-degrees-C. With monometallic platinum catalysts, the specific reaction rate was found to increase with increasing particle sizes from 1.5 to 15 nm, indicating that the reaction can occur preferentially on large platinum planes. This result was confirmed through addition of gold selectively deposited on the edges and corners of platinum particles. The selectivity pattern obtained suggests that the formation of strongly adsorbed species (NO22-) is favoured on small platinum particles of higher oxidation state.