NEW ACTIVE-SITE FOR CO HYDROGENATION FORMED ON PROMOTED RH CATALYST BY SPILLOVER HYDROGEN

By adding TiO2 and Cr2O3 to a Rh/SiO2 catalyst, Their effect on CO hydrogenation was studied with pulse surface reaction rate analysis (PSRA) and steady-state reaction under pressure. Chemisorption measurement indicated that these oxides covered a part of the Rh metal surface. TPR or O2-uptake measurement suggested that the oxides on the Rh metal particles were reduced partially by spillover hydrogen. PSRA revealed that the oxides added increased the rate constant of the step of C-O bond dissociation. As a result, turnover frequency (TOF) was also increased. This promotion effect was explained in terms of the newly formed active site composed of surface Rh atom(s) and a partially reduced cation of the oxide on the Rh metal particles. On such an active site, C-O bond is dissociated in the way that the oxygen side is bound to the partially reduced cation. High oxophilicity of the partially reduced cation must be the cause for the promotion in CO hydrogenation.