The Preparation Of Ni/Bentonite Catalyst And Its Catalytic Property Research To The Hydrogenation Of Nitrobenzene To Aniline

Ni based catalyst has attracted much attention for its excellent catalytic activity in many reactions. Bentonite is a superior resource in Guangxi district. Catalyst using bentonite as support, could be applied to synthesis by nitrobenzene hydrogenation, which can further broaden the application scope and improve the additional value of bentonite. Moreover, aniline is a kind of promising chemical raw material for more than 300 products were produced by aniline. As the development of society, the demand of aniline is further increase.The preparation technics and catalytic property of Ni/bentonite catalyst were studied using nitrobenzene hydrogenation to synthesis aniline as a probe reaction. The paper mainly including three parts which are shown as follows:Firstly, Ni/bentonite catalysts have been prepared by impregnation method with different nickel content and characterized by XRD, H2-TPR, H2-TPD, XPS etc. The H2 gaseous space velocity (GHSV) and nitrobenzene liquid space velocity (LHSV) were used to investigate the effect on the hydrogenation reaction. The results indicated that Ni/bentonite catalysts with 20 wt% nickel content show higher dispersion and smaller crystallite size of metallic Ni. Reaction carried out at 300 ℃ with GHSV at 4800 mL·gcat-1·h-1 and LHSV at 4.8 mL·gcat-1·h-1 over Ni/bentonite with 20 wt% nickel content, providing 95.7% conversion of nitrobenzene and 98.8% selectivity of aniline. However, Ni/bentonite catalysts with 20 wt% nickel content deactivated after 11 h while LHSV was 3.6 mL·gcat-1·h-1.Secondly, to improve the stability of Ni/bentonite catalysts, acid treated bentonite was applied to prepare Ni/acid treated bentonite catalysts with various Ni content using CTAB as dispersion agent by microwave assistant method. Ni/acid treated bentonite catalysts were characterized by XRD, SEM, N2-asorption/desorption etc. The experimental results indicated that microwave assistant method enhanced the dispersion of metallic Ni and increased the interaction between Ni and support. The reaction temperature, GHSV and LHSV were also investigated to confirm the impact of these conditions to the hydrogenation reaction. Reactions carried out at 300 ℃ with GHSV at 4800 mL·gcat-1·h-1 and LHSV at 3.6 mL·gcat-1·h-1 over Ni/acid treated bentonite dried by microwave assistant with 15 wt% Ni content, providing more than 99% conversion of nitrobenzene and about 95% selectivity of aniline during 60-hour reaction process. Moreover, carbon deposition was generated when nonuniform heating of product produced by nitrobenzene hydrogenation.Thirdly, Ni-B/acid treated bentonite catalysts were prepared by introduced B to Ni/acid treated bentonite catalyst to improve its resistance of carbon deposition. Ni-B/acid treated bentonite catalysts with 0.75 wt% B content was reduced at 500 ℃ using H2 as reductant and Ni2B was formed because of the combination of B and more active sites of Ni during the reduction process. The combination of B and Ni could prevent the hydrogenation reaction of nitrobenzene on metallic Ni that was easy to coke, which retard the formation of carbon deposition on the surface of Ni-B/acid treated bentonite catalyst. Reactions carried out at 300 ℃ with GHSV at 4800 mL·gcat-1·h-1 and LHSV at 3.6 mL·gcat-1·h-1 using Ni-B/acid treated bentonite catalysts with 0.75 wt% B content, providing more than 99.2% conversion of nitrobenzene and around 96% selectivity of aniline during a 105-hour reaction process. The lifetime of Ni-B/acid treated bentonite catalyst with 0.75 wt% B was increased from 60 h to 105 h compared to Ni/acid treated bentonite catalyst without B, which demonstrated that carbon deposition could be retarded apparently with the addition of B.