Kinetic analysis of reduction process of supported Rh/Al2O3 catalysts by time resolved in-situ UV-vis spectroscopy

Kinetic analysis of reduction of Rh/Al2O3 with low Rh-loadings (0.01-0.1 wt%) has been carried out by time resolved in-situ UV-vis spectroscopy. Based on XAFS and UV-vis spectra, it was indicated that Rh was present as surface isolated Rh3+ on catalyst calcined at 773 K in air. The rate of reduction of Rh3+ to metallic Rh was determined by in-situ UV-vis measurements under a flow of 1%H-2/He at 523-823 K. The reduction rate increased with Rh-loading but decreased as the calcination temperature elevated. The decrease of metallic Rh-0 formation with the calcination temperature was in harmony with the reaction rate of CO oxidation. The apparent activation energy (E-a) for the reduction of Rh3+ to Rh-0 was found to be constant around 60-62 kJ mol(-1) and independent of the calcination temperature and the Rh-loading, indicating the equivalent intrinsic activity of supported Rh species on Rh/Al2O3 with the low Rh-loadings. (C) 2012 Elsevier B.V. All rights reserved.