FTIR Spectroscopic Study of CO Adsorption on Cu/SiO2: Formation of New Types of Copper Carbonyls

Adsorption of CO on a reduced Cu/SiO2 catalyst (1 wt% Cu) results in formation of Cu0–CO species characterized by an IR band at 2128 cm−1. During the contact of the sample with CO two new species characterized by bands at 2045 and 2018 cm−1 appear. Experiments on 12CO–13CO co-adsorption prove that they are carbonyls. The 2045 cm−1 species are assigned to Cu0(CO)2 geminal complexes formed on copper atoms with a low coordination number. During evacuation the geminal species lose one CO ligand, thus being converted into linear carbonyls (band at 2018 cm−1). Both species are not affected by hydrogen, but easily disappear in the presence of small amounts of oxygen.