SiC nanowire supported Pd for efficient flow hydrogenation of nitroarenes to arylamines

Abstract

A highly efficient continuous-flow catalytic system for the ambient hydrogenation of nitroarenes to arylamines was developed using a 1 wt% Pd catalyst supported on robust, chemically stable SiC nanowires (Pd/SiC NWs). This system achieved 97% conversion and 98% selectivity for converting 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) within 5 minutes using NaBH₄ as a hydrogen donor. A pseudo-first-order reaction rate constant of 0.753 min⁻¹ was determined, which is 4.5 times greater than that observed in a batch reaction system and significantly surpasses rates achieved with Pd supported on other common carriers (activated carbon, silica, and alumina) and other noble metals (Pt, Au, and Ag) supported on SiC NWs. The reaction system demonstrated high stability and a broad substrate scope for various substituted nitroarenes. The high catalytic activity is attributed to the synergistic interaction between the Pd catalyst and the SiC NW substrate, which enhances the dissociation of NaBH₄ to produce H* and facilitates the subsequent transfer of H* to the substrate, resulting in the formation of mobile and reactive Si–H* species. This process promotes the hydrogenation of the preferentially adsorbed 4-NP on SiC NWs. Furthermore, the forced mass transfer and the uniformity of the reaction microenvironment, which prevent back-mixing of reactants and intermediates in the flow system, ensure the sequential hydrogenation of the –NO₂ group via the Haber direction route mechanism, with nitroso as the primary intermediate. This research offers a promising approach for the efficient and convenient synthesis of arylamines.