INFRARED STUDY OF SUPPORTED RHODIUM CATALYSTS EXPOSED TO CO H2 MIXTURES AT HIGH-PRESSURE AND TEMPERATURE

Infrared spectra have been recorded of Rh/SiO2 catalyst exposed to CO/H2 mixtures at various temperatures (473-553 K), pressures (3-50 atm) and CO:H2 ratios (1:14 to 14:1). Information was gained about surface hydroxyl groups on the support, the formation of gaseous methane, adsorbed carbon monoxide on rhodium and surface species containing alkyl groups. The dominant observed products of reaction were methoxy and ethoxy groups on the silica support, methane and higher hydrocarbons consisting predominantly of methylene chains. Depending on reaction conditions selectivities could be widely varied to give product distributions including 100% methoxy/methanol, a high proportion of ethoxy/ethanol or 100% higher hydrocarbon. Methane became more favoured at higher temperature, methanol rather than ethanol was favoured at low temperature and high pressure and higher hydrocarbons were favoured by CO-rich feedstock. - Reaction Of CO/H2 over Rh/Al2O3 and Rh/TiO2 gave higher selectivity to methane than Rh/SiO2 and also led to adsorbed carboxylate species on the oxide supports. The products were in part formed by catalysis involving the oxide components of the catalysts.