The interaction of coadsorbed potassium with π-orbital containing molecular adsorbates (benzene, PF3, NO, C4H8, and CH3CN) on the Pt(111) crystal face was studied by thermal desorption spectroscopy. Coadsorbed potassium significantly weakened the platinum-benzene bond. More of the benzene desorbed intact upon heating, instead of dissociating to yield H2 and surface carbon. In contrast, in previous studies it was shown that coadsorbed potassium substantially increases the platinum-carbon bond strength for adsorbed CO.1 Adsorbed NO was found to dissociate in an amount proportional to the K concentration, yielding N2 and N2O (as well as NO) in the desorption spectra. The adsorption of PF3, C4H8, and CH3CN was blocked by potassium, and no additional or shifted peaks were observed. A molecular orbital description is given to account for the potassium-induced effects. We propose that only adsorbates having molecular orbitale with energy levels located near to Ef can be significantly affected by "electronic promotion" in catalysis.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry