Reaction of Methane with MOx/CeO2 (M = Fe, Ni, and Cu) Catalysts: In Situ Studies with Time-Resolved X-ray Diffraction

Changes in chemical state and structural transformations occurring in a series of MOx/CeO2 (M = Cu, Ni and Fe) powder catalysts upon reaction with methane were investigated using in situ time-resolved X-ray diffraction (TR-XRD), ex situ X-ray absorption near edge structure (XANES)/extended X-ray absorption fine structure (EXAFS) spectroscopy, and X-ray photoelectron spectroscopy (XPS). XPS shows the presence of adsorbed CHx and COx species after exposing the powder catalysts to methane at room temperature. Temperature-programmed reduction (TPR) measurements point to reaction of the samples with methane and formation of CO, CO2, and H2O gas at temperatures as low as 100 °C. The TR-XRD results show that all of the transition-metal oxides in the as-prepared catalysts can be reduced to their metallic phase during the CH4-TPR process with the ceria support undergoing significant reduction from surface to bulk, yet the reduction temperature varies for different MOx/CeO2 samples. Among these samples, CuOx/CeO2 s...