Macroporous Carbon-Supported Fe-Based Catalysts for the Solvent-Free Oxidative Coupling of Benzylamine

Transition metal and nitrogen codecorated carbon materials have recently emerged as robust and efficient heterogeneous catalysts because of their unique electronic structure, superior activity, and high metal utilization. The most popular synthetic strategy for those catalysts is the direct pyrolysis of C- and N-containing precursors and metal salts, but the obtained products often suffer from structural heterogeneity of the active metal sites and poor mass transport. Herein, a hard template-assisted metal coordinated polymer is developed to synthesize a series of three-dimensional (3D) M-600-X (M = Fe, Co, Ni, Cu; X = 700, 800, 900 °C) catalysts with an advanced trimodal pore structure via a well-controlled two-step pyrolysis. Due to a preliminary annealing at 600 °C, it is possible to control the coordination configuration of the M–Nx moiety and the metal speciation by regulating the subsequent pyrolysis temperature. The 3D Fe-600-800 catalyst exhibited excellent catalytic performance in the oxidative coupling of benzylamine under solvent-free conditions due to the active Fe–N3 moiety as well as the synergy between the atomic Fe sites and the Fe/Fe3C nanoparticles. Moreover, this synthetic approach can also be employed in gram-scale production, and the obtained catalysts still possess superior activity and favorable stability, even in large-scale imine production. Thus, this work enables the rational design of cost-effective carbon-supported transition metal-based catalysts for highly efficient organic transformation.