Chemisorption bond energies of Lewis acids and bases on chemically modified Mo(100) surfaces

The acid-base properties of three molybdenum (100) surfaces chemically modified by 1.0 monolayers of oxygen, 1.0 monolayers of carbon and 0.8 monolayers of sulfur were investigated by thermal desorption spectroscopy using a series of molecular Lewis bases. The molecules used were of two types, lone pair bases, ammonia, phosphine, dimethyl ether and carbon monoxide, and olefinic bases, ethene, propene and 3,3,3-trifluoropropene. Carbon monoxide and 3,3,3-trifluoropropene were also capable of functioning as π acids. The trends in desorption energies are consistent with the expectation that the more electronegative oxygen creates more highly acidic adsorption sites. The desorption energies are compared with proton affinities. Of the three surfaces studied the acidity of the oxygen modified surface correlates best with the acidity of a gas phase proton.