The structure and activity of titania supported cobalt catalysts

Abstract

A series of titania supported cobalt catalysts (0.5–6%) were prepared by incipient wetness impregnation, and were characterized by ESCA, XRD, and hydrogen chemisorption. After calcination at 400°C, a surface CoTiO 3-like phase was the main species present in the 0.5 and 1% cobalt catalysts. For higher cobalt loadings, discrete Co 3O 4 particles were formed in addition to surface CoTiO 3. ESCA indicates that after reduction the cobalt metal particle size (6–13 nm) increases with increasing cobalt loading, but does not vary with reduction temperature (400–500°C). Hydrogen chemisorption was found to be activated and suppressed. The extent of hydrogen chemisorption suppression increases with increasing reduction temperature and decreasing cobalt particle size. The turnover frequency (based on cobalt dispersion derived from ESCA) for benzene and CO hydrogenation decreases with increasing reduction temperature and decreasing cobalt particle size. The decline in activity correlates with the extent of suppression of H 2 chemisorption. The results were interpreted in terms of a decrease in the fraction of exposed surface cobalt due to site blocking by reduced TiO x moieties.