Modification of the supported Cu/SiO2 catalyst by alkaline earth metals in the selective conversion of 1,4-butanediol to γ-butyrolactone

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The promotion effects of alkaline earth metals (Mg, Ca, Sr, Ba) on the catalytic property of the Cu/SiO2 catalyst for the gas phase dehydrogenation of 1,4-butanediol were investigated. The addition of Ca, Sr or Ba to the Cu/SiO2 catalyst resulted in the improvements of the catalytic activity and the γ-butyrolactone selectivity, and the Cu-Ba/SiO2 catalyst gave 99.6% yield of γ-butyrolactone even after 900h running. The catalysts were prepared by co-impregnation and characterized by N2 physisorption, X-ray diffraction (XRD), SEM, TEM, H2-temperature programmed reduction (H2-TPR), N2O-decomposition, ammonia temperature-programmed desorption (NH3-TPD), CO2-TPD, XPS, and FTIR spectroscopy of adsorbed pyridine and CO. On the base of the experimental results, two types of copper species on the reduced catalyst were proposed. The Cu° account for the dehydrogenation of 1,4-butanediol, while the electropositive copper species (Cu+) is suggested to be the strong Lewis acid site to catalyze side reactions. The selectivity of γ-butyrolactone was increased with the increasing of the Cu0/Cu+ ratio, and the yield of γ-butyrolactone was increased with copper surface area. The main byproduct 2,3-dihydrofuran may be formed from 1,4-butanediol by the metal/acid–base concerted catalysis.