CO AND NO INTERACTION WITH PD-AG AND PD-CR BIMETALLIC CATALYSTS .1. X-RAY-DIFFRACTION, INFRARED-SPECTROSCOPY, AND THERMOREACTION

Well-defined Pd-based bimetallic catalysts have been prepared and characterized. X-ray diffraction shows that in Pd-Ag, Ag has a strong tendency to segregate at the surface of the catalyst. On the other hand, in Pd-Cr, Cr is well distributed in the network of Pd and induces an electronic structure modification of Pd. The adsorption and coadsorption of CO and NO on these solids were studied by infrared spectroscopy and thermodesorption and compared with similar adsorptions on pure palladium and rhodium. It was shown that although the adsorption energies of CO and NO on the various catalysts are similar, upon coadsorption of the two reactants the surface coverage by NO is 4 to 20 times larger than by CO. Silver decreases this CO coverage and chromium slightly increases it. When a thermoreaction is performed at 430 K, appreciable amounts of N2 and CO2 are evolved from Pd, Pd-Cr, and Rh catalysts; Pd-Cr is more reactive than Pd and Pd-Ag is unreactive. (C) 1994 Academic Press. Inc.