Study On The Preparation Of Platinum-Acidic Ionic Liquid Bifunctional Catalyst And The Catalytic Synthesis Of P-Aminophenol

p-Aminophenol (PAP) is an important intermediate for organic synthesis and is widely used for the production of medicine, dyestuff, rubber and photographic chemicals, etc.. In this study, to settle the problems, such as the use of sulfuric acid, in the production of PAP through catalytic hydrogenation of nitrobenzene, a novel catalyst system, composed of metallic Pt and acidic ionic liquid, was designed and prepared to develop the environmentally benign technology for PAP synthesis.A novel quaternary ammonium type of Brφnsted acidic ionic liquid, N,N,N-trimethyl-N- sulfobutyl hydrogen sulfate ([HSO₃-b-N(CH₃)₃]HSO₄), was synthesized through a two-step method. FTIR, NMR, ESI-MS and elementary analysis were used to characterize its structure. The ionic liquid showed a high catalytic activity for the rearrangement of phenylhydroxylamine. A supported ionic liquid catalyst, [HSO₃-b-N(CH₃)₃]HSO₄-SiO₂, was prepared using sol-gel method. Under the optimized conditions, the phenylhydroxylamine conversion and PAP selectivity over the supported catalyst were 100% and 60.5%, respectively.A novel highly efficient bifunctional catalyst system, Pt/SiO₂+[HSO₃-b-N(CH₃)₃]HSO₄, composed of hydrogenation sites in solid state and rearrangement active sites in liquid state was designed and prepared for the nitrobenzene hydrogenation to PAP. The effects of the amount of Pt/SiO₂ catalyst, ionic liquid concentration, reaction medium, promoter, and reaction conditions on the nitrobenzene hydrogenation were investigated. The best amount of Pt/SiO₂ catalyst and suitable ionic liquid concentration were determined, and were 5wt% and 22.5wt%, respectively. Under the suitable conditions, the nitrobenzene conversion and PAP selectivity over the bifunctional catalyst were 96.6% and 81.4%, respectively. The catalytic activity was higher than that of sulfuric acid system, which was attributed to the solubility enhancement of nitrobenzene due to the nature of quaternary ammonium type of acidic ionic liquid. The structure of the recovered ionic liquid showed a good stability, and the catalytic activity of the bifunctional catalytic system was no obvious deactivation after recycled 3 times.Using the acidic ionic liquid [HSO₃-b-N(CH₃)₃]HSO₄,a novel method for simultaneously preparing of the uniformly dispersed Pt nanoparticles without using polymer as protecting agent, and a novel bifunctional catalyst with metallic and acidic active sites was developed. TEM, UV-Vis, FTIR, XPS, and XRD were used to characterize its structure. The Pt nanoparticles had a face-centered cubic structure with diameters about 3nm, and could be maintained in good dispersed state for more than 4 months.The pseudo homogenous bifunctional catalyst Pt-[HSO₃-b-N(CH₃)₃]HSO₄ was prepared by direct method. The effects of the preparation conditions, such as alcohol/H₂O ratio, reflux time and different alcohol, and the reaction conditions, including content of Pt nanoparticles, ionic liquid concentration, temperature, and H₂ pressure, on the nitrobenzene hydrogenation to PAP were investigated. Under the suitable conditions, the nitrobenzene conversion was 99.3%, and the PAP yield was 77.5%. In addition, it was found that the ionic liquid served not only as the acidic catalyst, but also the stabilizing agent to inhibit the aggregation of Pt nanoparticles.The immobilization of Pt-ionic liquid catalyst was studied through sol-gel, impregnation and chemically bonded method.The bifunctional catalyst, Pt-[HSO₃-b-N(CH₃)₃]HSO₄/SiO₂, was obtained by embedding ionic liquid into silica particles though sol-gel method. The effects of amount of Pt, preparation temperature, ethanol amount and aging time on the catalyst performance for nitrobenzene hydrogenation to PAP were investigated. Under the optimized conditions, the nitrobenzene conversion and the PAP yield were 66.7% and 28.8%, respectively.Pt-[HSO₃-bmim]HSO₄/SiO₂ bifunctional catalysts were prepared by successive impregnation and co-impregnation methods. The effects of loadings, dry, and reduction on its catalytic activity were investigated. Under the optimized conditions, the nitrobenzene conversion and the PAP yield were 68.6% and 41.4%, respectively.A novel Br?nsted type of acidic ionic liquid 1-vinyl-3-sulfobutyl imidazolium hydrogen sulfate, [HSO₃-bvim]HSO₄, was synthesized, and immobilized on silica gel, functionalized by sulphydryl, via free radical chain transfer reaction to obtain [HSO₃-bvim]HSO₄/SiO₂ solid acid catalyst. Then metallic Pt was supported on it using chemical reduction method to obtain the bifunctional catalyst Pt-[HSO₃-bvim]HSO₄/SiO₂. The catalyst showed a relative lower activity for nitrobenzene hydrogenation to PAP due to the less amount of ionic liquid bonded on the silica and the space hindrance effect. However, with the chemical bond, catalytic stability of it was better than those of the catalysts prepared by sol-gel and impregnation methods.