Rh promotional effects on Pt-Rh alloy catalysts for chemoselective hydrogenation of nitrobenzene to p-aminophenol

Hydrogenation of nitrobenzene to p-aminophenol over solid metal catalysts in acid medium is a sustainable and efficient protocol. However, it is challenging to fabricate such a catalyst that can achieve both high activity and unparalleled selectivity. Herein, a facile incipient wetness impregnation strategy is proposed and employed to synthesize an activated carbon supported Pt-Rh alloy catalyst. The Pt-Rh/AC catalyst exhibits simultaneously improved activity (TOF value: 10872 h-1) and p-aminophenol selectivity (ca. 95.4 %). The enhanced activity is attributed to the formation of well dispersed Pt-Rh bimetallic nanoparticles caused by the promoting effect of Rh for the reduction of Pt2+. Chemisorption and in situ infrared studies reveal that Pt-Rh bimetallic nanoparticles surfaces were enriched by Pt accompanying with possible electron transfer from Rh to Pt. The density functional theory calculations suggest that the adsorption of generated phenylhydroxylamine intermediate was inhibited over electron-rich Pt to avoid its subsequent hydrogenation to form aniline, resulting in excellent selectivity forp- aminophenol.

Automated summary

A activated carbon supported Pt-Rh alloy catalyst was synthesized using a facile incipient wetness impregnation strategy, and showed improved activity and selectivity for the hydrogenation of nitrobenzene to p-aminophenol. The presence of Rh promoted the formation of well dispersed Pt-Rh bimetallic nanoparticles on the catalyst surface, accompanied by possible electron transfer from Rh to Pt. Density functional theory calculations indicated that the electron-rich Pt inhibited the adsorption of the generated phenylhydroxylamine intermediate, resulting in excellent selectivity for p-aminophenol.