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

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 Cu2+-CO carbonyls. Decrease of the coverage is accompanied by decomposition of the OH-CO and Cu2+-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 (CO)-C-12 and (CO)-C-13. 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 Cu2+-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 Cuo-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. (C) 2002 Elsevier Science B.V. All rights reserved.