Catalysis by Transition Metal Carbides. VI. Hydrogenation of Carbon Monoxide over WC, W2C, and W Powder Catalysts

Abstract

WC, W2C, and W were comparatively studied for CO hydrogenation to reveal the catalytic role of carbon alloyed with metals. The main products of the reaction were CH4, CO2, and H2O on these catalysts, but the kinetic data obtained for WC catalyst were different from those for W2C and W catalysts: i.e., the apparent activation energies for CO consumption and for CH4 formation on WC were found to be about three times larger than those on W2C or W. Furthermore, the catalytic activity of WC was about 20 times larger than that of W2C and W. It was suggested that the hydrogenation of CO on WC proceeds via direct hydrogenation of adsorbed CO forming a CHO adsorbed species as an intermediate, whereas on W2C and W catalysts, dissociation of CO occurs in the initial step, followed by further hydrogenation of adsorbed carbon to form CH4. X-ray photoelectron spectroscopic (XPS) studies on WC and W2C showed that the WC surface catalytically activated was almost free from graphite carbon and oxygen as poison, but W2C surface was largely covered with graphite carbon. These distinctive catalytic behavior differences between the carbide catalysts are discussed on the basis of the structure of the active surfaces.