The multi-surface structure and catalytic properties of partially reduced WO3, WO2 and WC + O2 or W + O2 as characterized by XPS

The XPS at different experimental conditions of WO3, WO2, W(0), WC,W(0) + O2 and WC + O2 are reported. Extensive hydrogenolysis reactions of 2-methylpentane yielding methane a major product were observed on relatively pure W(0) and WC surfaces. Isomerization reactions for the same reactant were observed on WO2 or partially oxydized W(0) and WC surfaces, while bulk WO3 does not show any catalytic reactivity at the beginning of the reaction. The catalytic activity of WO2 is attributed to the presence of a certain density of states of the 5d, 6s electrons present at the Fermi-level on the W4+ cation and observed in the XPS of the valence band energy region of WO2. Such reduction by H2 and the hydrocarbon reactant of bulk WO3 or that present on W(0) or WC surfaces results in the presence of WO2 and to a lesser extent WO and W(0), which explains the isomerization reactions carried on these modified surfaces.