Special direct route for efficient transfer hydrogenation of nitroarenes at room temperature by monatomic Zr tuned α-Fe2O3

Abstract

Determining the route of a heterogeneous catalytic reaction is an important step in studying the reaction mechanism as well as improving reaction activity. As for the widely reported transfer hydrogenation of nitroarenes to aniline, many reported works have made simple judgements about the reaction route based on the “direct route” and “condensation route” proposed by Haber in 1898. Herein, detailed mechanistic experiments and DFT calculations helped us identify a special direct reduction route that goes through Ph-NO2 → Ph-NHOH → Ph-NH2 without the widely recognized Ph-NO intermediate for the transfer hydrogenation of nitroarenes to anilines by monatomic Zr tuned α-Fe2O3. In this catalytic system, Zr0.025Fe0.975Oy-350 can achieve complete transfer hydrogenation of nitroarenes at room temperature, where the parent α-Fe2O3 is inactive. Accompanying spectroscopic characterizations and calculations illustrate that the incorporation of Zr into the crystal lattice of α-Fe2O3 can effectively reduce the electron cloud density of surface iron species. The resulting special Fe(3+α)+-O(2+β)--Zr(4-γ)+ structure has greatly enhanced Lewis acidity, that promotes the decomposition of N2H4·H2O to form active [H] for the reduction of nitroarenes. Moreover, the structure is also beneficial for the adsorption of nitroarene with weakening of the NO bond. The present work can be extended to the application of non-noble metal oxides in the transfer hydrogenation of nitrobenzene under mild condition, and provides a significant method for exploring the reaction process of a heterogeneous catalytic reaction.