Real-time XAFS analysis of Rh/alumina catalyst

Reduction rates of rhodium supported on alumina were investigated with in situ time-resolved X-ray absorption fine structure (XAFS). The catalytic sample was prepared with 0.5-wt% rhodium on the alumina powder by a usual impregnation method. Two types of XAFS techniques were applied for the experiments: energy-dispersive XAFS and usual step-scanning XAFS. The reduction rates of the rhodium supported on alumina after oxidizing treatment at 500 degrees C were measured with dispersive XAFS. The reducing condition was with 3% H(2) in He at various temperatures from 100 to 250 degrees C. The spectra of Rh K-edge X-ray absorption near edge structure (XANES) were acquired every 0.2 s. The oxidation state of the rhodium was evaluated by the energy shift of Rh K-edge. The reduction rate of the rhodium was on a line in an Arrhenius plot. Reduction of the rhodium on the alumina in 3% H(2) in He at 900 degrees C after high temperature oxidization at 900 and 1000 degrees C were measured with step-scan XAFS. Though a portion of the rhodium was reduced in a few minutes, the residual rhodium was hardly reduced. The hardly reducible rhodium was considered to be reacted with the alumina support and lost catalytic activities. The ratio of the deactivated rhodium has been estimated as a function of the oxidization temperature and period. Copyright (C) 2008 John Wiley & Sons, Ltd.