Interaction of potassium with π-electron orbital containing molecules on Pt(111)

The interaction of coadsorbed potassium with p-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 E_f can be significantly affected by "electronic promotion" in catalysis. © 1983 American Chemical Society.