Study On The Selective Hydrogenation Of P-chloronitrobenzene To P-chloroaniline Over Mesoporous TiO₂Supported Pt（Fe）

Chloroanilines are an important class of industrial intermediates, which have beenwildly used in the fields of medicine, pesticides, dyes, etc. Chloroanilines are mainlysynthesized by the reduction of chloronitrobenzene. The main reduction methodsinclude iron powder reduction method, alcali sulphide reduction method and catalytichydrogenation reduction method, etc. The catalytic hydrogenation reduction processreceived much attention due to the advanced process, the environmental friendly andthe high quality product, etc. It has been reported that the catalysts forchloronitrobenzene hydrogenation mainly include the supported precious metals (Pt,Rh, Ir, Ru, Au), Raney Ni and amorphous alloy catalysts. The hydrogenation ofp-chloronitrobenzene to the corresponding p-chloroaniline is always accompanied bysome dechlorination reaction over these catalysts, which not only reduces the qualityof the products, but also contributes to the corrosion of the reactor. Although addingdechlorination inhibitor into reaction mixture can inhibit the dechlorination in a certainextent, the separation of products is difficult. It has been difficult issue to restraineffectively dechlorination reaction during the hydrogenation of chloronitrobenzene athome and abroad.Mesoporous titanium dioxide supported platinum catalysts (Pt/meso-TiO2) wereprepared by impregnation reduction method, and the influence that the support, activecomponent Pt load, transition metal additives, catalyst preparation conditions andreaction conditions for the catalytic activity and selectivity were investigated in thisstudy. The structures of catalysts were characterized by XRD, BET, TEM, etc. Theresults showed that the Pt/meso-TiO2exhibited excellent catalytic performance for thecatalytic hydrogenation of p-chloronitrobenzene to p-chloroaniline. Mass ratio activityof the Pt in the0.1wt%Pt/meso-TiO2for hydrogenation of p-chloronitrobenzene nearlydoubled and hydrodechlorination reduced when the Pt content in the Pt/meso-TiO2reduced from0.3wt%to0.1wt%. TEM results indicated that the excellent catalyticperformance of0.1wt%Pt/meso-TiO2for p-chloronitrobenzene hydrogenation was due probably to the improvement of Pt dispersity and the enhancement of the interactionbetween Pt nanoparticles and meso-TiO2. The undesired hydrodechlorination ofp-chloronitrobenzene on0.1wt%Pt/meso-TiO2catalystcould be completely avoided byusing1-propanol or2-propanol as solvent. Reaction temperature、H2pressure hadsignificant effect on the substrate reactivity and product selectivity.313K and higherH2pressure were more favorable for p-chloroaniline synthesis.Catalytic performance of transition metal (Fe, Ni, Co) modified Pt/meso-TiO2catalysts for hydrogenation of p-chloronitrobenzene to p-chloroaniline was alsoinvestigated in this paper. The results found that Fe doped meso-TiO2supported Ptcatalyst showed high activity and excellent selectivity for the hydrogenation ofp-chloronitrobenzene to p-chloroaniline. Catalytic hydrodechlorination ofp-chloronitrobenzene could be completely inhibited over2wt%Fe doped meso-TiO2supported0.1wt%Pt catalyst.