Infrared studies of carbon monoxide and hydrogen adsorbed on silica-supported iron and cobalt catalysts

Abstract

A temperature-programmed infrared study of carbon monoxide and carbon monoxide-hydrogen mixtures adsorbed on silica-supported iron and cobalt catalysts was made. Bands observed at 2181 and 2169 cm −1 for carbon monoxide on cobalt and iron, respectively, were attributed to physical adsorption on oxide impurities. For cobalt a band observed in the range 2020 to 2060 cm −1 increased in frequency within this range as the CO pressure was increased. This change in frequency was pressure reversible. This has been interpreted in terms of the number of CO ligands bound to one cobalt atom. In the presence of iron a mixture of carbon monoxide and hydrogen gives rise to methane as well as to a small amount of ethane plus traces of propane. Preadsorption of hydrogen leads to formation of methane only. In the presence of cobalt, mixtures of carbon monoxide and hydrogen only give methane. A band attributed to linearly held carbon monoxide on cobalt has been correlated with methane formation. An intermediate complex formed between adsorbed carbon monoxide on cobalt and hydrogen, stable within the temperature range 125 to 195 °C, has been inferred from the limited methane formation within this temperature range.