Preparation, Characterization And Catalytic Performance Of Ni/TiO₂Catalyst

Maleic anhydride can be produced by the oxidation of coking benzene or butane. It is the world’s third-largest anhydride except phthalic anhydride and acetic anhydride. The hydrogenation of maleic anhydride can produce a series of valuble chemical raw materials, such as succinic anhydride、γ-butyrolactone、tetrahydrofuran and1,4-butanediol et al. They have been widely used in petroleum processing、medicine and other fields. The research of prepration of catalyst with high activity and selectivity for the directed synthesis of maleic anhydride downstream products by the selective hydrogenating of C=C and C=O in maleic anhydride molecule is concerned widespreadly by the industry and academia.Currently, the catalysts for maleic anhydride hydrogenation mainly include precious Pt and Pd, of Ru and non-precious metals Cu, Ni Catalysts. Due to low cost, high activity and selectivity in the hydrogenation of maleic anhydride, Nickel-based catalyst has the most industrial applications prospects. Up to now, the researches about Ni-based catalysts for maleic anhydride are focused on investigating the effect of preparation method, morphology, size and electric configuration of Ni. However, the support effect was rarely studied. The research about hydrogenation of unsaturated carbonyl compounds such as crotonaldehyde and citral found that TiO2support can be reduced into TiOx species during the reduction process. The synergistic effect between TiOx species and the active ingredient can improve the the hydrogenation activity and selectivity of C=O. Maleic anhydride molecule is composed by a conjugated C=C bond, two C=O bond and a C-O-C bond. Maleic anhydride is a kind of typical α,β-unsaturated carbonyl compounds. The effect of TiOx species on hydrogenation activity and selectivity of C=C、C=O or C-O-C of nickel-based catalysts have not been reported yet.Based on the preliminary work of our research group. Our purpose is to reveal the effect and mechanism of TiOx species on the catalytic performance of Ni/TiO2catalyst in hydrogenation of maleic anhydride. To achieve this aim, We used BET, XRD, H2-TPR, H2-TPD, CO-TPSR characterization methods to find out the impact of support preparation method, reduction temperature and Ni content on catalyst textures structural properties and catalytic performance of Ni/TiO2catalyst in hydrogenation of maleic anhydride.The main results and conclusions are as follows:1. Different preparation methods of TiO2have different impacts on texture and structure properties of TiO2. The TiO2prepared by the sol-gel method exhibited both of anatase and rutile phase. It has a relatively large specific surface area. It’s easier for the TiO2prepared by the sol-gel method to reduce into TiOx species in Ni/TiO2catalysts. At the same time, the Ni component supported on TiO2prepared by the sol-gel method have a high degree of dispersion. Because of the synergistic effect of the smaller Ni grains and TiOx species, the hydrogenation activity of C=O of this catalyst is significantly higher than the catalyst whose support is prepared by hydrothermal method and precipitated method.2. We research the effect of the formation of TiOx species on the catalytic performance of Ni/TiO2catalysts in hydrogenation of maleic anhydride. The amount of TiOx species increase with the rising of reduction temperature. The formation of TiOx species makes the electron transferred from support to active Ni component. The effect of electron transport improves the H2activation ability of active Ni component. The hydrogenation ability of C=C bond is improved with the increase of TiOx species amount. But the hydrogenation ability of C=O improved first, then reduces. When the reduction temperature is450℃, the catalyst exhibited the highest hydrogenation activity of C=O. The reason for this phenomenon might be the amount of TiOx species is too much which makes catalysts’ surface is electron rich. That caused the repulsion between catalysts and O atom in C=O bond. As a results, the probability of collision between the catalyst and C=O reduces. Based on this reason, the hydrogenation activity of C=O in Ni/TiO2catalyst reduces.3. Nickel content have a great impact on the selectivity of y-butyrolactone in Ni/TiO2catalyst. In the range of5%to13%, the specific surface area of active component Ni increased first and then decreased. The amount of TiOx species increases with the rising of Ni content which improves the activation ability of H2on the surface of active Ni component. The activation ability of H2and the probability of collision with the C=O achieve the best match when Ni content is7.5%. At this time, the catalyst showed the best hydrogenation activity of C=O.