Study On The Synthesis Of P-Aminophenol Over Metal / Solid Acid Catalyst

A single-step reaction of nitrobenzene (NB) into p-Aminophenol (PAP) through catalytic hydrogenation is a widely used synthesis route for PAP. SO₄^2-/ZrO₂ and S₂O₈^2- /ZrO₂ as solid superacid were prepared for the substitute of H2SO4 ,which resulting the strong causticity and the large amount of sewage in the production, and various factors which affect the solid acid on structure and acidity were investigated. And then a metal-solid superacid bi-functional catalyst was prepared for the purpose to implement the catalytic hydrogenation of nitrobenzene to PAP in nonacid medium.SO₄^2-/ZrO₂(SZ) and S₂O₈^2- /ZrO₂(PSZ) solid superacid were prepared by microemulsion The factors which affect the solid acid on the formation, structure, acidity and catalytic activity were by the measurements of XRD, NH3-TPD, BET, XPS, Py-IR etc. SZ and PSZ prepared by microemulsion had large special surface aera and their particle size were about 10 nm. The pH of microemulsion, calcinations atmosphere and calcinations ways affected greatly on formation and structure of solid acid. The sample had the largest special surface aera when pH is about 9.0.Different calcination temperatures affect samples obviously on acid amount, acid type and acid strength distributation. The B acid amount of sample surface was large relatively at low calcination temperature. The L acid amount gradually increased with the increasing of calcination temperature. A mass of high strength L acid sites were formed on the sample surface at crystal temperatures. The formation of L acid sites with stronger acid strength might be related to the formation of tetragonal phase of ZrO₂. Effect of calcination temperatures on the catalytic activity of samples was obvious. The PAP yield over SZ catalyst could reach 30.6% at calcination temperature of 600℃, while over PSZ catalyst the optimization yield of PAP was 33.8% at calcinations temperature of 550℃.The reaction condition of nitrobenzene hydrogenating to PHA and PHA rearrangment to PAP were investigated respectively. The lower temperature, higher pressure and a properly addition of DMSO were all favorable for the enhancement of PHA selecitivity. Using water as solvent and a higher temperature were favorable for PHA rearrangement on solid acid catalysts.The effect of Pt loading on thet acidity and activity of S₂O₈^2-/ZrO₂ catalyst was investigated. It could be found that the loading of Pt could increased the acid amount of the sample ,but decreased the acid strength. The way of Pt loading had great effects on the acidity and activity of catalyst. When Pt wsa loaded on S₂O₈^2-/ZrO₂, the L acid amount on the catalyst surface increased mostly and rearrangement reaction activity lowered.while,when Pt was loaded on S₂O₈^2-/Zr(OH)₄, the B acid amount increased and rearrangement reaction activity was closed to the acivity of unloaded catalyst.The reaction of catalytic hydrogenation of nitrobenzene to PAP was investigated over Pt- S₂O₈^2-/ZrO₂ catalyst in the water medium at the temperature of 150℃and H2 pressure of 0.5MPa. In this condition, the rearrangement reaction on acid sites made more competitive The decreasing of Pt loading amount could restrain hydrogenation rate in a degree and improve the competition between rearrangent and hydrogenation to enhance PAP yield and selectivity.