Electronic interactions in the rhodium/TiO2 system

Abstract

A variety of electron spectroscopic techniques has been used with model catalysts fabricated on single-crystal substrates to study charge transfer in the RhTiO2 system. In order to avoid the morphological changes and encapsulation that occur when catalysts are reduced at high temperatures to induce SMSI, TiO2 substrates have been reduced by inert gas ion bombardment prior to Rh deposition. Comparison of model catalysts prepared on reduced supports with those prepared on fully oxidized supports indicates that electronic charge is transferred from reduced Ti cations to Rh particles, resulting in a partially ionic RhTi bond. The RhTi bonding may provide a driving force for encapsulation of the Rh but does not lead to a large-scale suppression of the capacity of the Rh to chemisorb CO. We also present the first direct evidence for modification of the valence levels of the Rh due to the presence of the encapsulating Ti suboxide moieties during SMSI.