THE MULTISURFACE STRUCTURE AND CATALYTIC PROPERTIES OF PARTIALLY REDUCED WO3, WO2 AND WC-2 OR W+O-2 AS CHARACTERIZED BY XPS(O)

The XPS at different experimental conditions of WO3, WO2. W(0), WC, W( 0) + O-2 and WC + O-2 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 s urfaces, 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 electron s 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 H-2 and t he hydrocarbon reactant of bulk WO3 or that present on W(0) or WC surf aces 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.