INFRARED STUDY OF CO ADSORPTION ON ALUMINA-SUPPORTED PALLADIUM PARTICLES

We have studied the adsorption of CO on small palladium particles depo sited on a well-ordered thin Al2O3 film on NiAI(110) using infrared re flection absorption spectroscopy (IRAS). Recent studies in our group w ith STM and SPA-LEED have shown that the deposited particles are predo minantly terminated by (111)-type surfaces. The IR spectra exhibit sev eral absorption bands, which are associated with linearly bound CO (20 90-2120 cm(-1)) and bridge bonded CO (1930-1970 cm(-1)). On the larger , better ordered palladium aggregates another GO-induced band appears in the region of 1970-2000 cm(-1), which we assign to CO molecules bou nd on the edges of the particles. Evaporation of Pd in presence of a C O atmosphere leads to the formation of a palladium carbonyl-like compo und which is stable only at low temperatures. The IR spectra of this s pecies show apparent similarities with the spectra of CO on the small particles. (C) 1998 Elsevier Science B.V. All rights reserved.