EFFECTS OF ADSORBED OXYGEN-CONTAINING MOLECULES ON THE XANES OF PT IN SUPPORTED PT/SIO2 CATALYSTS

The variation of the X-ray absorption coefficient above the Pt-L(III) edge after adsorption of crotonaldehyde, butyraldehyde, crotylalcohol and butanol on a Pt/SiO2 catalyst was studied by means of X-ray absorption spectroscopy. The adsorption of these molecules caused the intensity of the white line to decrease in the order CrHO > CrOH approximately BuHO much greater than BuOH. From this we concluded that adsorbed unsaturated compounds donate electrons from their double bonds to Pt. The magnitude of the observed effects was approximately equal for the C=O and the C=C group. Over the Pt/SiO2 catalysts studied, crotonaldehyde was concluded to be adsorbed via both double bonds. The interaction of the free electron pairs of the oxygen was concluded to be significantly weaker than the interaction of the electrons in the pi-bonds.