Catalytic Performance Of Ni/Al₂O₃-SiO₂ Catalyst For Liquid Phase Hydrogenation Of Maleic Anhydride To γ-butyrolactone

y-Butyrolactone, is an important fine chemical product and excellent solvent with high boiling point. Because of special molecular structure, y-butyrolactone can produce a series of high-value derivatives, such as a-pyrrolidone, N-methyl pyrrolidone and polyvinyl pyrrolidone, et al. All these products are important intermediates in pesticides, pharmaceuticals and dyes. Meanwhile, y-butyrolactone is an excellent organic solvent with high-boiling point and exhibits high conductivity and stability. It can be used as electrolyte of lithium batteries and electrical appliances.The main methods for y-butyrolactone production include furfural method,1,4-butanediol dehydrogenation, hydrogenation of Maleic acid dimethyl esters and direct hydrogenation of maleic anhydride. The method of direct hydrogenation of maleic anhydride has some advantages in the production of y-butyrolactone such as short process, environmental benign and high economic efficiency. Synthesized y-butyrolactone by direct hydrogenation of maleic anhydride contains two steps. In a first step, the hydrogenation of the C=C bond in maleic anhydride produces succinic anhydride. Then, the hydrogenolysis of one C=O bond in succinic anhydeide gives y-butyrolactone. The hydrogenation of C=C bond is easier over metal catalyst. However, the hydrogenation of C=O bond is more difficult. At present, to improve the C=O hydrogenation activity and yield of y-butyrolactone, methods such as introducing second component or adjusting the composition ratio of each component are used to reduce the gain size and improve the dispersion of the active metal. Few studies are reported for investigating the effect of supports on the catalytic activity of catalysts in maleic anhydride hydrogenation. The researches about investigating the support effects suggest that the support can improve the hydrogenation activity of catalyst by changing the interaction between metal and support. Whether there is a synergistic effect between the support and active metal, in the hydrogenation of maleic anhydride to y-butyrolactone, is obscure.Based on preliminary work of our research group, Ni/Al2O3-SiO2 catalysts were prepared by impregnation method and applied in the liquid phase hydrogenation of maleic anhydride to y-butyrolactone. Effects of structure, texture and surface property on catalytic performance of catalyst were studied by N2 physical adsorption, XRD, H2-TPR, H2-TPD, NH3-TPD-MS, TG-DTA and TPO-MS. Based on the experimental results, the synergistic effect between the Al2O3-SiO2 support and active metal Ni0 during the C=O bond hydrogenation was discussed.The research content is listed as follows:1. The Ni/Al2O3-SiO2 catalysts with Ni content of 12.5 wt% were prepared by impregnation method, using 10 wt% Al203-Si02 as supports. The differences between Ni/Al2O3-SiO2, Ni/Al2O3 and Ni/SiO2 catalysts in catalytic performance of catalysts for maleic anhydride hydrogenation to y-butyrolactone were investigated. The results showed that the C=O hydrogenation activity of Ni/Al2O3-SiO2 catalyst is much higher than Ni/SiO2 and Ni/Al2O3 catalyst. Subsequently, the highest yield of y-butyrolactone was obtained over Ni/Al2O3-SiO2 catalyst. Characterization results demonstrated that there are abundant L acid sites over the surface of Ni/Al2O3-SiO2 catalyst. The L acid sites can interact with C=O bond by accepting lone electron pair of oxygen atom in C=C bond. The interaction between L acid sites and C=O bond promote the hydrogenation of C=O bond with active H atom adsorpted on the surface of Ni0, producing y-butyrolactone.2. To further understand the effect of surface property on adsorption and activation of C=O bond of Ni/Al2O3-SiO2 catalyst, a series of Ni/Al2O3-SiO2 catalysts with different Ni content were prepared and applied in the liquid phase hydrogenation of maleic anhydride. With the nickel content increased from 5 wt% to 12.5 wt%, the adsorption and activation ability of H2 was improved, the yield of y-butyrolactone was increased significantly. Further increasing the nickel content to 20 wt%, the adsorption and activation ability of H2 was further improved, the yield of γ-butyrolactone was increased slowly. It is attributed to the acid center numbers decreased, which was caused by too much nickel species covering on the surface of catalysts. The ability of adsorption and activated C=O was weakened. When the nickel content is 12.5 wt%, there is a best match between the hydrogenation activity and the adsorption and activation capabilities of C=O bond.3. The stability of 5 wt%,12.5 wt% and 20 wt% Ni/Al2O3-SiO2 catalysts were investigated. The amount and strength of surface acidity of the catalysts was decreased when nickel content increased. The numbers of high carbon species, formed during maleic anhydride hydrogenation were reduced. Thereby stability of the catalysts was significantly improved.