Preparation Of Ni And Pt Supported Catalysts And For Hydrogenation Of Nitrobenzene

Hydrogenation of aromatic nitro compounds plays an important role in industrial,and the obtained products are widely used in the medicine,pesticides,dyes and rubber and other fields.Nowadays,there are many catalysts for hydrogenation of aromatic nitro compounds,among which the supported catalyst has a big specific surface area and can stabilize the active components through the carrier.Therefore,highly efficient supported catalysts have always been one of the important research topics in the field of catalysts.In this paper,using nickel and platinum as active components and Mg-Al hydrotalcite as carrier precursor,then calcinated and gas phase reduced to get a series of catalysts to catalytic hydrogenation of nitrobenzene.The main contents and conclusions are as follows:(1)The Ni/Mg(Al)O catalysts were synthesized by one-step coprecipitation method.The effects of Ni loading,reaction temperature and pressure on the hydrogenation of nitrobenzene to aniline were investigated.The experimental results show that the suitable Ni loading,temperature and high pressure are favorable for the reaction.At 120 ℃,1.5 MPa,the yield of aniline was 99% over 10%Ni/Mg(Al)O catalyst in n-heptane solvent.(2)The 0.5%Pt/Mg(Al)O catalysts were synthesized by the some method,and the effects of reaction pressure,solvent,Mg/Al molar ratio and calcination temperature on the hydrogenation of nitrobenzene to aniline were investigated.The following conclusions were drawn: 0.5%Pt/Mg(Al)O catalyst showed the highest activity,At30 ℃,2.5 MPa,the yield of aniline was >99% in n-heptane solvent within 4 h.In order to explore the reasons for the excellent activity of the catalysts,we used a variety of characterization methods to characterize the physicochemical properties of the catalysts.The characterizations of 0.5%Pt/Mg(Al)O catalyst show that the morphology of the active component Pt is nanoparticles with an average particle size of about 2.25 nm and is uniformly dispersed on the Mg-Al composite oxide carrier.On the other hand,the large specific surface area and abundant alkaline sites of the carrier also play an important role in the highly selective synthesis of aniline from nitrobenzene.(3)The 0.1%Pt/Mg(Al)O catalyst was synthesized by same method,and the effects of reaction time,pressure,temperature,solvent and Pt loading on the hydrogenation of nitrobenzene to azobenzene were investigated.We concluded that 0.1%Pt/Mg(Al)O catalyst showed the highest activity,at 70 ℃,0.5 MPa,the yield of azobenzene was 90%in n-heptane solvent within 1.6 h.A number of isolated bright spots appeared in the acHAADF-STEM image,which were confirmed to be Pt atoms,which indicated that the active component of the catalyst was single atom morphology.Then three other precious metal catalysts(Ru,Ir,Au)were prepared,and the experimental data showed that the hydrogenation product of nitrobenzene was aniline.It is obvious that different active components have different catalytic behaviors in the catalytic process.Then,compared with the reported catalysts,the mechanism of hydrogenation of nitrobenzene reaction catalyzed by 0.1%Pt/Mg(Al)O catalyst was simply speculated.