Model studies on segregation and catalytic properties of supported Pt-Rh nanocatalysts

In this work, a comprehensive report is presented on model investigations on the surface composition and catalytic activity of supported Pt-Rh nanocatalysts and their dependence on the impurity and the metal-support interactions. Monte-Carlo (MC) simulations indicate that sulphur can influence the surface composition very strongly; but the influence of metal-support interaction on the surface composition is insignificant. A microkinetic analysis has been made to investigate the role of alloying and impurity on the CO+O 2 , CO+NO, CO+NO+O 2 reactions over these nanocatalysts. For the CO+O 2 reaction the alloy particles show an intermediate activity compared to that on Rh and Pt nanoparticles. On the other hand, for the CO+NO reaction the alloy particles show no synergistic effect of alloying. The effects of alloying on the kinetics of CO+NO+O 2 and CO+NO reactions are found to be identical. Sulphur has been found to reduce the activity of the Pt-Rh nanocatalysts for the CO+O 2 , CO+NO and CO+NO+O 2 reaction more through blocking of the active sites on the surface than through changes in surface composition. The effect of sulphur is much stronger on CO 2 formation rate than on N 2 formation rate. N 2 formation takes place more through recombination of N atoms (β - N 2 ) than through N 2 O formation and its subsequent dissociation into N 2 and O (δ - N 2 ). N 2 formation rate is found to be the same for CO+NO and CO+NO+O 2 reactions. Implications of these results are thoroughly discussed.