Preparation, Characterization Of Ni/TiO₂-SiO₂ And Catalytic Performance For Maleic Anhydride Hydrogenation

Maleic anhydride is a very important organic chemical raw materials. There are many of its downstream products such as succinic anhydride, y-butyrolactone, tetrahydrofuran and 1,4-butanediol, which have a wide range of development and application prospects. With a large-scale production of maleic anhydride, The low-cost synthesis of high value-added chemicals from maleic anhydride attracted much attention. However, In the catalytic hydrogenation of maleic anhydride downstream products, the use of different catalysts and process conditions, raw material conversion and the selectivity of target products are very different. Therefore, the study prepared by high-performance catalyst for selective hydrogenation of maleic anhydride is a theoretical and practical value of the research topic.TiO2 can be reducible and is a strong interaction between the active component, so that the TiO2 as the support of the metal catalyst showed unique catalytic properties. TiO2 has been reported in the literature load Pd, Ni and other metals, at higher temperatures after reduction by H2, the catalyst will produce the TiOx(x<2) species, which can modify the surface of the load of metal and promote the-C=O,-N=O hydrogenation. However, due to TiO2 has some weaknesses, such as small specific surface area, phase instability and poor mechanical strength, making it difficult to widely used in industry, in order to overcome these shortcomings, researchers launched a multi titanium composite oxide carriers. Typically a TiO2-SiO2 mixed oxides, combined SiO2 with TiO2 can not only solve the shortcomings of small specific surface area, poor thermal stability and mechanical strength, but also modulate the nature of the support by changing the composition of complex oxides, to apply to the requirements of different types of hydrogenation reactions.This article on the basis of previous work in the laboratory, TiO2SiO2 aerogel with different TiO2 content were prepared by Sol-Gel method. Ni/TiO2SiO2 catalysts were then prepared by an impregnation and were applied to the selective hydrogenation of maleic anhydride (MA) to y-butyrolactone (GBL). All the catalysts were characterized by IR-spectroscopy(FT-IR), N2 adsorption, temperature-programmed reduction(H2-TPR), X-ray diffraction(XRD), diffuse reflectance infrared fourier transform spectroscopy(in-situ DRIFTS) and H2 temperature-programmed adsorption-mass spectroscopy techniques (H2-TPD-MS) etc. In order to reveal catalyst surface properties and catalytic activity relationship in the maleic anhydride hydrogenation, we investigate the effects of different Ti content, different nickel content and the different reduction temperature on the catalyst structure, surface properties and catalytic activity. The main results and conclusions are as follows:1. TiO2-SiO2 aerogel were prepared by Sol-Gel method combined with supercritical fluid drying, which precursors were TEOS and TBOT respectively. FT-IR, TG-DSC, XRD results indicate, TiO2 and SiO2 are not simple mixture, Ti ion into the skeleton structure of SiO2 and interact each orther, forming a Ti-O-Si bond, this would had a significant impact on the change of Sample surface area, surface hydroxyl groups, and other physical and chemical properties of the crystalline phase.2. By analyzing content of titanium, nickel loading and catalyst reduction temperature on the Ni/TiO2-SiO2 hydrogenation catalyst structure and performance of MA, we believe that the better Ni/TiO2-SiO2 MA hydrogenation catalyst should not only the activity of both a small grain to provide a larger NiO nickel active surface in order to generate more dissociative adsorption of hydrogen, but also has some TiOx to activation of C=O bond. Only when the active surface of nickel and TiOx species attain the best match, the catalyst can have a good hydrogenation, this match can achieve by controlling the content of titanium on the support, nickel catalyst loading and activation conditions.3. The best catalyst for the mass fraction of nickel content is 20%, the optimal reduction temperature is 450℃. In the above optimal conditions, a reaction temperature of 240℃, H2 pressure of 5.0 MPa and time of 6h were afforded, Ni/TiO2-SiO2 catalyst was shown 100% conversion of MA and 95.1% selectivity of GBL.