An in situ infrared study of CO hydrogenation over silica and alumina-supported ruthenium and silica-supported iron

Abstract

The synthesis of hydrocarbons from carbon monoxide and hydrogen over Ru SiO 2 , Ru/Al 2O 3 , and Fe SiO 2 catalysts has been studied under reaction conditions by infrared spectroscopy. Other than CO, the surface species which are observed during reaction contain only carbon and hydrogen. Strong CH 2 bands arising from long chain saturated hydrocarbons are observed at low reaction temperatures ( T < 473 K) with ruthenium but not with iron. With increasing temperature, these CH 2 bands on Ru decrease and are replaced by a single broad band. This may be a composite of CH 2 and CH 3 groups having one or at most a few carbon units attached to the metal surface. At these higher temperatures the spectra from Ru SiO 2 and Fe SiO 2 catalysts become similar, suggesting common surface intermediates. Additionally, at these temperatures bands corresponding to gas phase products (methane, ethane, propane) are also observed. Differences in the temperature dependence of the hydrocarbon bands from Ru SiO 2 and Fe SiO 2 are shown to be consistent with other published results. No evidence is found for the existence of hydroxy carbene or formyl species during reaction, adding to growing evidence that hydrocarbon synthesis over ruthenium and iron proceeds via initial formation of surface carbides.