Studies On Gold Supported Catalysts For Nitrobenzene Hydrogenation

Aniline is the very important raw material for the production of fine chemicals and p-aminophenol is an important pharmaceutical intermediate.Catalytic hydrogenation of nitrobenzene is the most suitable green process for the industrial production of aniline and p-aminophenol.But the presence of poor selectivity and stability,the difficulty to separation and recovery,and requirement of phase transfer catalyst for the common catalyst,i.e.platinum loaded on the activated carbon(Pt/C),greatly limit its industrial applications.Therefore,it is very of significance to research and develop new catalysts to overcome the above problems for the catalytic hydrogenation of nitrobenzene.At present,titanium dioxide(P25)supported Au shows the high selectivity for the catalytic hydrogenation of aromatic nitro compounds,and Au is relatively cheaper than Pt,but organic solvents such as toluene are used as the reaction medium.In the paper,with water as the green reaction medium,and with hydrophilic titanium dioxide as a catalyst carrier,the influence of carrier type,preparation method,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 and p-aminophenol.The conclusions were as follows:(1)Supported Au catalysts were preparated by precipitation-deposition using different crystalline titanium dioxide as a carrier and the performance of the catalytic hydrogenation of nitrobenzene was compared.The carriers and the corresponding catalysts were characterized by N2 adsorption-desorption,XRD,UV-vis,TG,and TEM.It was found that anatase titanium dioxide(TiO2-A)with high specific surface and good hydrophilicity loaded Au catalyst showed the best performance.And the preparation and reduction methods for this catalyst were studied.The results indicated that the Au catalyst prepared by the thermal decomposition exhibited the best performance.(2)With Au/TiO2-A as a catalyst,the influence of Au load,amount of catalyst,H2 pressure,reaction temperature and time on the catalytic hydrogenation of nitrobenzene was investigated.It was found that under the conditions of Au loading of 1.5%,H2 pressure of 0.4 MPa,the reaction temperature of 90 ?,and the time of 4 h,the hydrogenation conversion rate of nitrobenzene reached the highest.While the recycling performance after the catalyst regeneration was studied,the results showed that the recovered catalyst can be regenerated by heat treatment in air and can be used repeatedly for 4 times without obvious loss of activity.(3)With nitrobenzene as the raw material,and Au/TiO2-A as catalyst,the effect of a sulfuric acid concentration,a mixed solvent ratio of ethanol and water,H2 pressure,catalyst loading on catalytic hydrogenation of nitrobenzene was investigated.It was found that the catalyst selectivity for the p-aminophenol was the highest at the sulfuric acid concentration of 15%,the catalyst showed the best performance at ethanol and water ratio of 1:2 and a better selectivity under H2 pressure of 0.6 MPa.With increasing the amount of catalyst,the conversion rate of nitrobenzene was enhanced,whereas the selectivity decreased a little.