Infrared and X-ray photoelectron spectroscopy studies of carbon monoxide adsorbed on silica-supported cobalt catalysts

Abstract

The adsorption of CO on silica-supported cobalt catalysts has been studied by means of i.r. and X.p. spectroscopies in order to reveal the nature of Co—CO bonding in connection with the catalytic hydrogenation of CO. For a 7.5 wt% catalyst, a single i.r. band for CO appeared first at ca. 2000 cm–1(band A). With increasing exposure to CO this band shifted to 2040 cm–1, accompanied by a sharp band B at 2180 cm–1. In contrast, a 3.35 wt% catalyst produced only band B. Upon evacuation at room temperature, band B was readily removed, whereas band A, shifting to a lower frequency, remained up to 473 K. X.p.s. has revealed that the surface of the former catalyst has exposed metallic cobalt, whereas the surface of the latter consisted mainly of Co2+ ions even after exposure to H2 at 723 K. Bands A and B were assigned to linearly bonded CO on metallic sites and COδ+ on cationic sites, respectively. An analysis of the variation in frequency of band A as a function of the amount of CO suggested the presence of indirect interaction via the metal electrons. The effect of hydrogen was a shift in band A to lower frequency. This led to the conclusion of weakening of the C—O bond in the presence of H2 and no contribution from COδ+ species to the hydrogenation.