Catalytic reactions on well-characterized vanadium oxide catalysts. 1. Oxidation of carbon monoxide

The oxidation of carbon monoxide over unsupported and supported vanadium oxide catalysts was investigated from the standpoint of structure sensitivity. The activity of unsupported V₂O₅ catalyst changed greatly with the treatment of the catalyst: The fusion of unsupported V₂O₅ markedly decreased the turnover frequency, while the reduction-oxidation treatment of the fused catalyst increased it. The turnover frequency of V₂O₅/TiO₂ with low V₂O₅ content was much smaller than that of the V₂O₅/TiO₂ with high V₂O₅ content or the unsupported V₂O₅. Such a retarding effect of the TiO₂ support on the activity of the oxidation of carbon monoxide is in contrast to the known promoting effect of TiO₂ for the oxidations of various hydrocarbons. From these results coupled with the characterization of the catalysts, it was concluded that the oxidation of carbon monoxide on vanadium oxide catalysts is a structure-sensitive reaction and that the activity of surface defects such as steps, kinks, and vacancies is much higher than that of the surface V=O species in the smooth (010) face of V₂O₅.