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

Cu/SiO₂ catalysts prepared by differentmethods 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 ammoniaevaporation (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 C=O 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.