Characterization of Cu/MCM-41 and Cu/MCM-48 mesoporous catalysts by FTIR spectroscopy of adsorbed CO

Abstract

Adsorption of CO at 85 K on Cu/MCM-48 results in formation of Cu +(CO) 2 species (2162 and 2121 cm −1) H-bonded CO (2156 cm −1) and a negligible amount of Cu 2+CO carbonyls. Decrease of the coverage is accompanied by decomposition of the OHCO and Cu 2+CO species while the Cu +(CO) 2 dicarbonyls loose one ligand and are converted into Cu +CO species (2130 cm −1). The assignments are proved by co-adsorption of 12 CO and 13 CO . CO adsorption on the hydrogen-reduced sample provokes formation of Cu 0CO species characterized by a band at 2122 cm −1. The latter are easily decomposed upon evacuation. Low temperature CO adsorption on Cu/MCM-41 leads to formation of the same species as observed with Cu/MCM-48. In this case, the concentration of the Cu +CO species is higher and a significant amount of Cu 2+CO species is detected. These results suggest a higher dispersion of copper on MCM-41. The frequencies of the Cu +(CO) 2 (2163 and 2127 cm −1) and Cu +CO (2134 cm −1) species on Cu/MCM-41 are slightly blue shifted. The frequency of the Cu 0CO species (2125 cm −1) is also a little higher. In line with the higher copper dispersion, Cu/MCM-41 is superior to Cu/MCM-48 in its catalytic activity for the methanol decomposition to hydrogen and CO. The peculiarities of the samples depending on the preparation method are discussed.