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 Rh0 was determined by in-situ UV–vis measurements under a flow of 1%H2/He at 523–823 K. The reduction rate increased with Rh-loading but decreased as the calcination temperature elevated. The decrease of metallic Rh0 formation with the calcination temperature was in harmony with the reaction rate of CO oxidation. The apparent activation energy (Ea) for the reduction of Rh3+ to Rh0 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.

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► Kinetic analysis of the reduction of Rh3+ to Rh0 on Rh/Al2O3.
► In-situ UV–vis can monitor the dynamics of Rh/Al2O3 with very low Rh-loading.
► Reduction rate decreases with the increase in calcination temperature.
► Activation energy of the reduction is independent of the calcination temperature and the Rh-loading.