Kinetic Study on Solid-Phase Reduction of Silica-Supported Nickel Oxide Species

Abstract

ganic reaction mechanisms for metal species supported on solid particles and in solution. The advanced synchrotron radiation XAFS technique is originally developed and applied to catalysis and electrode reactions. AbstractThe X-ray absorption fine structure (XAFS) spectroscopy was used to analyze the chemical state conversion of the Ni species in SiO 2 -supported Ni catalysts which were prepared by the impregnation method with various Ni loadings. The in situ XAFS measurements revealed that the calcined NiO species was quantitatively reduced by H 2 to Ni(0) at around 580 K, and the formed Ni(0) species was reversibly and gradually oxidized by O 2 up to 873 K. The transmission electron microscopy observation clarified that the Ni(0) particle size was dependent on the Ni loading. The dynamic observations using the timeresolved dispersive XAFS technique showed that the reduction process could be described by the first-order kinetics on the Ni species, which was different from the reduction kinetics of supported PdO species, which is a divalent metal oxide for the same family element. The different reduction kinetics is ascribed by the different atomic arrangement in the crystal structure between NiO and PdO.