CO on Pd(100)/SiO2: a computational study of the effect of CaO on the energetics of adsorption

The semiempirical atom superposition and electron delocalisation molecular orbital (ASED-MO) theory was used to study the CO/Pd-Ca-SiO2 interaction. A ddition of a single CaO molecule to simulate a different interaction with b oth the metal and the CO molecule was also considered. Ca was added as a su blayer between the SiO2 and the metallic cluster. A simple diatomic CaO mol ecule was positioned on the Pd-21 surface. The energetics of CO adsorption was studied in both cases. In our adsorption scheme, CO was considered to b e perpendicular to the surface. The results indicate that in general adsorp tion on twofold sites seems to be more favourable. The Ca sublayer stabilis es CO adsorption by less than 0.1 eV for twofold short bridge adsorption si te. Fourfold site is de-stabilised by 0.6 eV and is 2 eV less favourable th an the twofold sites. The effect of Ca and CaO on the adsorption is of smal l magnitude. (C) 2000 Published by Elsevier Science B.V. All rights reserve d.