ADSORPTION OF ALDEHYDES AND KETONES ON PLATINUM AND PALLADIUM - INFLUENCE OF STEPS, OPEN FACES AND METAL NATURE - A THEORETICAL-STUDY

The adsorption geometries of formaldehyde, acetaldehyde and acetone on Pt and Pd surfaces have been studied by means of semi-empirical extended Huckel calculations: Pt(111), Pt(110) and Pd(111) surfaces have been compared. A Pt(111) surface with a (100) step has also been considered. For the three molecules, the preferred adsorption geometry is the eta2 di-sigma one on all surfaces, except for acetone on Pt(111) where the adsorption is eta1 on-top. The electronic factors which control the adsorption have been analyzed. The adsorption modes are found to be very sensitive to the repulsive four-electron interactions between the molecule and the surface. Surfaces for which these repulsive interactions are the smallest are favorable to eta2 adsorption with respect to eta1, coordination. This is the case for Pt(110), Pd(111) and steps on the Pt(111) surface. This effect is more sensitive for acetone adsorption and results in a change in the preferred adsorption mode.