Study On The Hydrogenation Performance Of Supported Platinum-based Catalysts Catalyzed By Chloronitrobenzene

Chloroaniline,as an important organic intermediate in the chemical industry,can be widely used in the synthesis of fine chemicals such as pharmaceuticals,pesticides,dyestuffs and pigments.Among the many production processes,the synthesis by the selective hydroreduction of chlorinated nitrobenzene to chloroaniline can effectively reduce the reaction time,the production cost and environmental pollution,while improve the product yield.This process is considered as an effective way to prepare chloroaniline.Therefore,it is of great practical importance to develop high performance and environmentally friendly hydrogenation catalysts.Loaded platinum-based catalysts are widely applied in green catalytic hydrogenation reactions due to their moderate reaction conditions and high activity.However,the occurring of hydrogenolysis and dehalogenation side reactions resulted in lower selectivity of the target product during catalytic hydrogenation.Therefore,the development of loaded platinum-based catalysts with high activity and selectivity is the focus in the selective hydrogenation of chlorinated nitrobenzene.To this end,a series of loaded platinum-based catalysts were prepared by the impregnation method and their performance in catalyzing the hydrogenation of chlorinated nitrobenzenes were initially evaluated in this paper.The physical and chemical properties of the catalysts as well as their carriers were characterized by XRD,N₂ adsorption and desorption,SEM,XPS,TEM-EDS,FT-IR and other techniques.The main works of this thesis as follows:（1）A series of Pt/OMC catalysts were prepared using ordered mesoporous carbon（OMC）as supports anchored with Pt nanoparticles.The ordered nature of their support structure could improve the diffusion transfer during the reaction process,and thus enhance the activity and selectivity of the catalytic chlorinated nitrobenzene hydrogenation reaction.The results shown that most of the Pt nanoparticles are uniformly distributed in their mesoporous pore channels for the prepared Pt/OMC catalysts.The anchoring of Pt nanoparticles by oxygen-containing groups on the support surface and the domain-limiting effect of the ordered mesoporous channels could positively regulate the size regulation of the metal particles,resulting in smaller Pt nanoparticles.Whereas,Pt particles were dispersed on the outer surface of the support and aggregated to a certain extent when the activated carbon（AC）was used as the support.The Pt/CMC-600 catalyst showed optimum catalytic activity（100%）and selectivity（>99%）in the hydrogenation of o-chloronitrobenzene at 60°C and 5 bar of H₂ for 60 min.This may be attributed to the synergistic effect of the body-centered cubic mesoporous carbon support（CMC）with Pt nanoparticles and the specificity of its pore structure.In addition,the Pt/CMC-600catalyst exhibited excellent d stability and could be recycled for multiple uses.（2）A series of Pt/Ga N_xO_y catalysts were prepared by using Ga N in rod shape as the support and loading nanoparticles via impregnation method.The effects of Pt content,Pt precursor type and reduction mode on their performance in catalyzing the selective hydrogenation of chloronitrobenzene were investigated,and the relationship between the structure and performance of the Pt/Ga N_xO_y catalysts was further explored.The evaluation results indicated that under the conditions of the 1-Pt _CW/Ga N_xO_y catalyst exhibited 100%substrate conversion rate and a steady-state selectivity more than 99%under 60℃and 5 bar for10 min.Its catalytic performance is superior to that of 1-Pt _CW/CMC and 1-Pt _CW/AC samples prepared under the same reaction conditions.This may be attributed to the abundance of defective sites in the Ga N_xO_y support,which can anchor the Pt precursors and promote the homogeneous dispersion of the Pt nanoparticles.In addition,the defective sites may facilitate the selective adsorption of-NO₂ groups in the substrate for catalytic hydrogenation reactions,thus improving the selectivity of the target products.In addition,the 1-Pt _CW/Ga N_xO_y catalyst also exhibited approved stability and could be recycled for multiple utilization.