CO- and N2-FTIR characterisation of oxidised Rh species supported on Ce0.68Zr0.32O2

Abstract

The identification of a Rh-oxidised species of a Rh(0.29)/Ce_0.68Zr_0.32O₂ catalyst that exhibits peculiar CO–O₂ kinetics [I. Manuel, J. Chaubet, C. Thomas, H. Colas, N. Matthess and G. Djéga-Mariadassou, J. Catal. 2004, 224, 269] is addressed. For this purpose, various catalysts are studied by XANES, CO- and N₂-FTIR, and benzene hydrogenation. The results obtained, particularly from N₂-FTIR, which is, to our knowledge, reported for the first time on this kind of catalyst, suggest that Rh is mainly stabilised as electron-deficient clusters (Rh_n^δ+) on a Rh(0.29)/Ce_0.68Zr_0.32O₂ catalyst after reduction at 500 °C under H₂. The existence of these species, which may be caused by either electron perturbation induced on the metal by the reduced support or electron withdrawal from the metal clusters by an inductive effect of the neighbouring Cl anions, is also revealed through CO-FTIR experiments. In the presence of CO, however, evidence of Rh^I(CO)₂ species is also provided.