CO on Pd(1 0 0)/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. Addition of a single CaO molecule to simulate a different interaction with both the metal and the CO molecule was also considered. Ca was added as a sublayer between the SiO2 and the metallic cluster. A simple diatomic CaO molecule was positioned on the Pd21 surface. The energetics of CO adsorption was studied in both cases. In our adsorption scheme, CO was considered to be perpendicular to the surface. The results indicate that in general adsorption on twofold sites seems to be more favourable. The Ca sublayer stabilises CO adsorption by less than 0.1 eV for twofold short bridge adsorption site. Fourfold site is de-stabilised by 0.6 eV and is 2 eV less favourable than the twofold sites. The effect of Ca and CaO on the adsorption is of small magnitude.