Synthesis of p-aminophenol by transfer hydrogenation of nitrobenzene with formic acid as a hydrogen source

Abstract

Pt/C and SO₄²⁻/ZrO₂ were mechanically mixed as the catalysts for p-aminophenol synthesis by catalytic transfer hydrogenation of nitrobenzene in water with formic acid as the hydrogen source. The effect of Pt loading and the solid acid on the reaction was investigated. PAP selectivity reached a maximum at a loading of 1 wt%. The characterization results revealed the presence of three valence states of Pt. Pt⁰ was beneficial for the nitrobenzene hydrogenation, while higher valence Pt contributed to the formic acid decomposition. The catalytic performance of different solid acid catalysts, including HZSM-5, Hβ, SO₄²⁻/ZrO₂ and SO₄²⁻/TiO₂, was compared. It was found that Lewis acid sites with strong acid strength were favorable for p-aminophenol formation, and SO₄²⁻/ZrO₂ showed higher catalytic activity for the reaction. Using Pt/C + SO₄²⁻/ZrO₂ as the catalyst, the reaction conditions were optimized. Under the optimal reaction conditions, the nitrobenzene conversion and the p-aminophenol selectivity were 80.0% and 47.6%, respectively. The reaction mechanism was also proposed based on the main by-products of the reaction.