Item

Abstract

We have studied the adsorption of CO on small palladium particles deposited on a well-ordered thin Al₂O₃ film on NiAl(110) using infrared reflection absorption spectroscopy (IRAS). Recent studies in our group with STM and SPA-LEED have shown that the deposited particles are predominantly terminated by (111)-type surfaces. The IR spectra exhibit several absorption bands, which are associated with linearly bound CO (2090–2120 cm⁻¹) and bridge bonded CO (1930–1970 cm⁻¹). On the larger, better ordered palladium aggregates another CO-induced band appears in the region of 1970–2000 cm⁻¹, which we assign to CO molecules bound on the edges of the particles. Evaporation of Pd in presence of a CO atmosphere leads to the formation of a palladium carbonyl-like compound which is stable only at low temperatures. The IR spectra of this species show apparent similarities with the spectra of CO on the small particles.