Role of D-Electrons in Chemisorption and Metal/Support Interactions Studied by Electron Spectroscopy. Progress Report, January 15, 1983-January 14, 1984

摘要

This research program is an investigation of the nature of the strong metal-support interaction (SMSI) between Rh metal catalysts and TiO sub 2 supports by using a variety of surface-sensitive electron-spectroscopic techniques to characterize the properties of model catalysts consisting of small Rh particles supported on single-crystal TiO sub 2 . Since the writing of the previous Annual Progress Report (DOE/ER/10830-1) we have further characterized the changes in the electronic structure of the surface cations of the support as a function of thermal processing, and we have also simulated with our model catalysts the processing that transforms catalysts to an SMSI state. Evidence has been found for the migration of a sub-oxide of Ti over the Rh particles during high temperature reduction, thus blocking the Rh sites for chemisorption. We are currently extending that work to high temperature oxidation of model catalysts followed by low temperature reduction in order to establish the reversibility of the SMSI transition. The electronic structure of the core levels of both the catalyst atoms and the ions of the support is being studied in order to determine the changes in oxidation state that accompany SMSI. We have also re-evaluated the theoretical work of Horsley on the charge transfer model of SMSI and shown that his results are irrelevant to the interaction of metal atoms with actual TiO sub 2 surfaces. The correct way to approach the problem of reduced TiO sub 2 surfaces has been described. (ERA citation 08:055112)