Adsorption and dissociation of CH 3OH on clean and K-promoted Pd(100) surfaces

Abstract

The adsorption and dissociation of methanol on clean and K-dosed Pd(100) surfaces were investigated in the temperature range 90–600 K. By means of photoelectron and thermal desorption spectroscopy, condensed layer, chemisorbed and dissociated methanol were distinguished. Methanol decomposes through the formation of a methoxy species. No adsorbed CH 3 was detected on clean Pd(100) in the course of heating of the adsorbed layer from 90 K to high temperatures. The cleavage of a methanolic CO bond, and the formation of a small amount of adsorbed CH 3 were observed only above 300 K, but during continuous dosing of the surface with CH 3OH. Additive potassium markedly increased the surface concentration of chemisorbed methanol and the formation of methoxy species, but it did not enhance the methanolic C-O bond breaking. A significant stabilization of methoxy was also experienced: its complete decomposition occurred at 450–500 K. In the discussion of the data, a direct chemical interaction between methanol and potassium and the formation of a stable KOCH 3 complex are proposed.