Synthesis of p-aminophenol from the hydrogenation of nitrobenzene over metal-solid acid bifunctional catalyst

BACKGROUND: A single-step conversion of nitrobenzene (NB) to p-aminophenol (PAP) through catalytic hydrogenation is a widely used synthesis route for PAP. The main shortcoming of this route is the use of sulfuric acid for rearrangement of the phenylhydroxylamine (PHA) intermediate. In this paper, S2O82-/ZrO2 (PSZ) solid acid and Pt-S2O82-/ZrO2 (Pt-PSZ) bifunctional catalysts were prepared for the synthesis of PAP in non-acid medium. RESULTS: Calcination temperature has a substantial effect on the acidity, structure and activity for PHA rearrangement of PSZ. The highest PAP yield was 33.8% over PSZ calcined at 823 K when the reaction was carried out in water at 423 K. A high PAP yield of 23.9% was achieved by a single-step reaction of nitrobenzene over Pt-PSZ bifunctional catalysts. CONCLUSION: PSZ solid acid exhibits high activity for PHA rearrangement. Perfect tetragonal ZrO2 and much stronger acid sites play important roles in catalytic activity. Inhibiting the hydrogenation activity by reducing the amount of Pt loading on Pt-PSZ can improve the competition of PHA rearrangement on acid sites with hydrogenation of PHA on metal active sites, resulting in better selectivity to PAP. (C) 2008 Society of Chemical Industry