Zirconium phosphate supported-silver nanoparticles for selective hydrogenation of nitrobenzene into azoxybenzene compounds

Abstract

In this work, zirconium phosphate (ZrP) supported Ag nanoparticle (NP) catalysts were constructed. The as-obtained catalysts were characterized thoroughly by XRD, HAADF-STEM, py-IR spectroscopy, etc. A coordination interaction was found between Ag NPs and the phosphate group on ZrP, and the acidic sites on ZrP played a very critical role not only in adsorbing nitrobenzene, but also in activating NaBH₄ to facilitate hydrogen transfer to Ag sites. It was indicated that the ZrP-supported Ag NP catalysts were highly active for catalytically selective hydrogenation of the substituted nitroarenes into azoxybenzene compounds by using NaBH₄ as a hydrogen source. Notably, the catalysts could afford a full conversion of nitrobenzene within 3 min and an exceptional selectivity to azoxybenzene. Moreover, 1%Ag/ZrP-R was recycled eight times without obvious loss of activity. No leaching of Ag species was observed in consecutive catalytic cycles. Methanol was found to be a superior solvent for this reaction and also acted as a hydrogen resource in the reaction. On the basis of the catalytic activity test and density functional theory (DFT) calculations, the reaction pathway was proposed as well. To our knowledge, the ZrP-supported metal catalysts are some of the best catalyst systems for selective hydrogenation of nitrobenzene into azoxybenzene compounds with exceptional activity and selectivity.