| In order to resolve the problem of separation and recovery of Pt/AC catalyst, impregnation and microemulsion methods were used to prepare SiO2-support metal Pt catalysts, which were used in the hydrogenation of nitrobenzene to prepare p-aminophenol (PAP). Meanwhile, the new technology of synthesizing PAP from nitrobenzene by employing acetic acid solution instead of sulfuric acid solution was studied. An preliminary exploration of the reaction from nitrobenzene directly to p-acetamidophenol (APAP) in acetic acid solution was made.As for Pt/SiO2 catalysts which were prepared by incipient impregnation, effects of various factors during the preparation precess, such as SiO2 supports with different texture, pH value of impregnation solution, drying process, calcination temperature and reduction conditions, on the structures and catalytic performances were investigated. The suitable conditions for preparing the catalysts were confirmed. The characterisation results of XRD and TEM indicated that the size of Pt particle directly reduced without calcination was obviously smaller than that calcined before reduction, and the activity was higher. In addition, the effects of different promoters such as Ru, Mo, Ba, Co on the performance of Pt/SiO2 catalyst were investigated. The results showed that performance of Pt-Co/SiO2 catalyst was better, and the yield of PAP was 81.4%.A series of ultrafine Pt-SiO2 catalysts were prepared by microemulsion method. Effects of different microemulsion systems, preparation temperature, NH4OH aqueous solution amount, Pt loading and the molar ratio of water to surfactant on the structures and catalytic performances of Pt-SiO2 catalysts were investigated. The optimal conditions for preparing the catalysts were confirmed, and the yield of PAP could reach 55.7%. The specific activity on per-unit surface of the Pt-SiO2 catalysts was higher than that of the Pt/SiO2 catalysts prepared by incipient impregnation. The characterisation results of XRD and TEM showed that the Pt-SiO2 catalyst prepared by microemulsions method had higher heat stability and the resistance to sintering in high temperature than the Pt/SiO2 catalysts prepared by incipient impregnation.The reaction conditions for catalytic hydrogenation of nitrobenzene to p-aminophenol wasinvestigated. CTAB was chosen as the phase transfer catalyst, whose optimal amount was 0.8(wt) percent of nitrobenzene. The optimal loading of Pt was 3wt%, and the weight ratio of the catalyst to nitrobenzene was 1:20. The optimal reaction conditions were as follows: reaction temperature 85 ℃, reaction time 4h, concentration of sulfuric acid 17.5wt%, the volume ratio of nitrobenzene to sulfuric acid 1:20. Under the above-mentioned conditions, the yield of PAP reached 78.8%. The catalyst showed a partial deactivation after reaction. The characterisation results showed that the reason for deactivation might attribute to the active centers on the surface of the catalyst being partially encapsulated by organic substances in the course of reaction. However the activity of the catalyst which had been regenerated did not drop after employed for five runs.For the sake of clean chemical production, the new technology of synthesizing PAP from nitrobenzene by employing acetic acid instead of sulfuric acid solution was studied. Effects of concentration of acetic acid solution, promoters on the reaction were investigated, and the maximal yield of PAP reached 50.2%. A preliminary exploration of directly synthesizing p-acetamidophenol from nitrobenzene in acetic acid solution was made. Although the yield of APAP was only 7.6% at present, the new technology simplified the separating operation.
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