Preparation And Application Of Pt/ZrO 2 And SO₄^2-/ZrO₂-Al₂O₃ Catalysts For Nitrobenzene Hydrogenation To Para-aminophenol

Para-aminophenol (PAP) is a commercially important compound which is wildly used as intermediate for the production of analgesic and antipyretic drugs, such as paracetamol and acetaminophen. The commercial manufacture of PAP is hydrogenation of nitrobenzene using mineral acid as the acid catalyst. The shortcomings of this route mainly involve the corrosion problems due to the necessary use of mineral acid and the loss of expensive active component of the catalyst. So a kind of environment friendly catalyst were proposed for the substitute of H2SO4 in this study, which including SO₄^2-/ZrO₂ and SO₄^2-/ZrO₂-Al₂O₃ solid superacid, and then the factors which affect the solid acid catalyst on structure and acidity were investigated. The optimal reaction conditions for the synthesis of PAP by hydrogenation of nitrobenzene using solid acid catalyst were studied.The technology to synthesis PAP by hydrogenation of nitrobenzene in liquid homogeneous system was studied, in order to study the effects of reaction conditions on yield of product, the reaction temperature, reaction pressure, concentration of sulfuric acid and the amount of the catalyst were investigated respectively. The optimal conditions of the reaction were as follows: 87℃of reaction temperature; 0.3Mpa of reaction pressure; 15% of the concentration of sulfuric acid; and NB/Pt=4000(w/w). Under these conditions, the selectivity of the reaction was 75.38%, and the conversion of the nitrobenzene was 86.84%.The SO₄^2-/ZrO₂ solid superacid was prepared by precipitation method. The factors which affected the solid acid catalyst on catalytic activity were studied, including pH, calcination atmosphere, calcination temperature and concentration of sulphuric acid. It shows that using ammonia as solvent, 9.0 of pH, impregnating in 1.0 mol/L H2SO4, and calcinating at 650℃with air give better results, Under these conditions, the catalyst has higher surface area, more acid sites, higher acid strength and catalytic activity. The SO₄^2-/ZrO₂-Al₂O₃ solid acid were prepared by coprecipitation method. In order to study the effects of preparation methods on catalytic activity, the way of adding A12O3 and quantity of A12O3 were investigated respectively. The catalysts were characterized by BET, XRD and TPD. It indicates that the introduction of Al₂O₃ not only make contribution to the structure of solid acid catalyst but also increase the acidity. The sample SZA-5 with Zr/Al molar ratio of 1:9, using coprecipitation method, impregnating in 1.0 mol/L H2SO4, calcinating at 650℃, shows better catalytic activity for the reaction of Bamberger rearrangement.Nitrobenzene hydrogenation to para-aminophenol over Pt/ZrO₂ and SO₄^2-/ZrO₂-Al₂O₃ solid acid catalyst were performed. The factors which affected the yield of PAP were investigated respectively, including the reaction temperature, reaction time, loading amount of Pt and kinds of solvent. The optimal conditions of the reaction were as follows: 80℃of reaction temperature; 3h of reaction time; 1% of Pt loading amount; and using water as solvent. Under these conditions, the selectivity of PAP was 74.91%, and the conversion of nitrobenzene was 44.82%.The SZA solid acid catalyst is easy to deactivate. However, it has been found that activity of SZA catalyst can be regenerated by calcining at certain temperature.