The Electronic State of Supported Rh Catalysts and the Selectivity for the Hydrogenation of Carbon Monoxide

Article abstract of DOI:10.1021/j100255a020

The electronic states of Rh crystallites highly dispersed on various oxides (SiO2, ZnO2, ZrO2, and ZrO2 or TiO2 on SiO2) and the catalytic hydrogenation of CO to form oxygenated hydrocarbons were examined.From XPS measurement, Rh on Rh/SiO2, showed an electronic state similar to that of Rh metal.This catalyst was active in forming hydrocarbons.However, Rh on Rh/ZnO, which was active in forming methanol, was in the Rh⁺ state.Rh crystallites supported on ZrO2 or TiO2 on SiO2 were active for producing C2 oxygenates.Rh on these oxides was in a state between that supported on pure ZnO and on pure SiO2.For the formation of C2 oxygenates, the ability first to dissociate CO and subsequently to insert CO are indispensible.It was found in this study that Rh⁰ was active for CO dissociation and that Rh⁺ was active for CO insertion reaction.Further, the Rh catalyst active in the formation of C2 oxygenates was in the electronic state between Rh⁰ and Rh⁺ and was active for both reactions, CO insertion and CO dissociation.