Selective hydrogenation of dimethyl maleate to tetrahydrofuran over Cu/SiO2 catalyst: Effect of Cu+ on the catalytic performance

Cu/SiO2 catalysts prepared by different methods have been investigated focusing on the influence of Cu+ on the catalytic performance. The composition, structure and copper valence state were characterized by means of BET, XRD, XPS, FTIR, N2O-titration. It was found that the Cu/SiO2 prepared by ammonia-evaporation (AE) method had much higher TOF value than that prepared by wetness-impregnation (WI) with the same THF selectivity. The higher TOF value was attributed to the coexistence of Cu+ and Cu0 species in the activated AE-Cu/SiO2, while only Cu0 species existing in the activated WI-Cu/SiO2. Researches suggest that Cu+ can adsorb and polarize the CO bond of DMM. It is concluded that Cu0 could be the main active site and the synergistic effect between Cu0 and Cu+ could contribute to hydrogenation of DMM to THF.