Combined in situXRD and in situXANES studies on the reduction behavior of a rhenium promoted cobalt catalyst

Abstract

A 10% Co–4% Re/(2% Zr/SiO₂) catalyst was prepared by co-impregnation using a silica support modified by 2% Zr. The catalyst was characterized by temperature programmed reduction (TPR), in situXRD and in situXANES analysis where it was simultaneously exposed to H₂ using a temperature programmed ramp. The results showed the two step reduction of large crystalline Co₃O₄ with CoO as an intermediate. TPR results showed that the reduction of highly dispersed Co₃O₄ was facilitated by reduced rhenium by a H₂-spillover mechanism. In situXRD results showed the presence of both, Co-hcp and Co-fcc phases in the reduced catalyst at 400 °C. However, the Co-hcp phase was more abundant, which is thought to be the more active phase as compared to the Co-fcc phase for CO hydrogenation. CO hydrogenation at 270 °C and 5 bar pressure produces no detectable change in the phases during the time of experiment. In situXANES results showed a decrease in the metallic cobalt in the presence of H₂/CO, which can be attributed due to oxidation of the catalyst by reaction under these conditions.