Studies On Gold Supported Catalysts For Liquid Phase Hydrogenation Of Nitrobenzene

As an important raw material for the production of fine chemicals and pharmaceutical intermediate, aniline has wide application and huge market prospect. The catalytic hydrogenation of nitrobenzene is the most suitable green process for the industrial production of aniline presently. In recent years, the titanium dioxide loaded nano-gold catalysts caused widespread attention for catalytic hydrogenating Nitro aromatic into amino aromatics with high selectivity. But also because of low hydrogenation activity, poor stability and using toxic organic solvents, it greatly limits its industrial applications. Therefore, it is very of significance to research and develop new catalysts and solvent to overcome the above problems for the catalytic hydrogenation of nitrobenzene. In the paper, using titania nanotubes which were hydrothermal synthesised in alkaline conditions as catalyst carriers, with water as the green reaction medium, and the influence of hydrothermal synthesis time, preparation method, carrier type, and the process parameters on the performance of Au catalytic hydrogenation of nitrobenzene was studied. The obtained results may provide the technical foundation for the development of green production processes of aniline. In this paper, a series of catalysts were also prepared with different oxides as the carriers, with toluene and water for solvents, the influence of the solvent effect on catalytic properties was investigated.The conclusions were as follows:(1) Study on the reaction of nitrobenzene hydrogenation with supported Au by TiO2 nanotubes:With titanium dioxide nanoparticles as the raw material, the titania nanotubes were prepared by hydrothermal synthesis in alkaline conditions, then supported Au catalysts were prepared by using the nanotubes as carriers. The polymorph of titania nanotubes, hydrothermal reaction time were also studied. The carriers and the corresponding catalysts were characterized by N2 adsorption-desorption, XRD, UV-vis, and TEM. It was found that the specific surface area of anatase titania nanotubes prepared by hydrothermal synthesis method was 193.52m2g-1, while the specific surface area of anatase TiO2 nanoparticles was 61.35m2g-1. At H2 pressure of 0.3MPa, the reaction temperature of 90℃, reaction time of 3h, using anatase titanium dioxide nanotubes(after hydrothermal reaction of 24 hours at 400℃) as carrier in catalytic liquid phase hydrogenation of nitrobenzene, the conversion rate can reach 79.28%, and TOF is 237.42mol·h-1·mol-1.The titania nanotubes supported gold catalysts reached the same conversion under the shorter reaction time, less pressure, lower temperature and milder conditions as compared to the anatase titania supported gold catalysts.(2) Study on the solvent effect of nitrobenzene hydrogenation to aniline:For the gold catalysts prepared by different oxides as carriers, under the same reaction conditions, the catalytic performance of liquid phase hydrogenation of nitrobenzene in water and toluene was compared. It showed that the catalytic properties changed with different solvents, the catalytic performance in water was significantly higher than that in toluene.