Analysis of Reaction Mechanism for Supported Metal Catalysts by Means of Time-Resolved XAFS Technique

Abstract

The redox reactions of supported metal species have been investigated by means of in-situ and time-resolved XAFS technique for the Co, Ni, and Cu catalysts supported on silica. The in-situ XAFS experiments revealed the chemical state conversions of supported metal species during the temperature-programmed reduction and oxidation processes. The small metal particles tend to be oxidized at lower temperature and reduced at higher temperature than the corresponding larger particles for the Co and Ni catalysts. The temperature shift is ascribed by the strong interaction of the divalent metal oxide with silica. The time-resolved XAFS measurements revealed the detail dynamic processes of redox reactions for the supported metal specie. The chemical state conversions of the supported Ni species under the mixed gas environment of CO and NO were studied by means of the time-resolved XAFS technique at 873 K. The faster oxidation of metallic Ni than the reduction of NiO were directly demonstrated, and the dynamic conversion of the Ni species thus indicated that the oxidation of CO and the reduction of NO were simultaneously achieved on the supported Ni particles.