In situ fourier transform infrared study of methanol synthesis on mixed metal oxide catalysts

Transmission infrared spectroscopy was used to characterize adsorbed species on methanol synthesis catalysts under reaction conditions. A copper carbonyl, bidentate formate, and methoxy species were identified as stable surface species. An adsorbed formaldehyde species was unstable at the reaction temperature, but could be observed on the catalyst surface at the beginning of the reaction. Surface species were very similar for feed mixtures of (1) carbon monoxide and hydrogen, (2) carbon monoxide, carbon dioxide, and hydrogen, and (3) formic acid and hydrogen. Carbon monoxide was adsorbed on copper sites to form a linearly bonded carbonyl species. The formate species was adsorbed on a zinc site different from the zinc site on which formaldehyde and methoxy groups were adsorbed. The rate-determining step in methanol synthesis was determined to be the reaction of hydrogen from a hydroxyl species with a methoxy group to yield methanol. It was established that at the experimental conditions used in this study, the methanol synthesis reaction was far from equilibrium while the water-gas shift reaction was near equilibrium.