Disentangling Structural and Electronic Roles of Pyridinic- and Pyrrolic-N in Ni-Catalyzed Hydrogenolysis of Aryl Ether Bonds

Abstract

Understanding how distinct nitrogen functionalities regulate metal sites remains a central challenge in the rational design of carbon-supported catalysts for hydrogenolysis reactions. Here, we disentangled the structural and electronic roles of pyridinic-N and pyrrolic-N in nitrogen-doped carbon-supported Ni catalysts by systematically tuning nitrogen speciation and investigating the hydrogenolysis of C–O bonds in diphenyl ether (DPE), a representative lignin-derived aryl ether. An optimized nitrogen-doped carbon-supported Ni catalyst (denoted as Ni/NC35) achieved complete DPE conversion under mild conditions (180 °C, 0.5 MPa H2, 1 h) with high selectivity toward cyclohexane and cyclohexanol. Comprehensive characterization and DFT calculations revealed that the appropriate incorporation of pyridinic-N and pyrrolic-N strengthened the metal–support interaction and effectively suppressed Ni nanoparticle aggregation, while synergistically regulating the electronic structure of Ni through both direct Ni–N coordination and non-coordinated modulation of neighboring Ni atoms, thereby promoting the formation of highly active electron-deficient Ni species. These electron-deficient Ni sites led to a modest increase in the energy barrier of C–O bond cleavage but significantly lowered the barriers for H2 dissociation and benzene formation, thereby enhancing the catalytic activity for DPE hydrogenolysis. The findings were consistent with the significantly higher activity of DPE hydrogenolysis and benzene hydrogenation over Ni/NC35 compared to the undoped catalyst (Ni/NC0). This work elucidates the key role of pyridinic-N and pyrrolic-N in structural optimization and electronic regulation of Ni-based catalysts and provides clear design principles for engineering non-noble metal catalysts for selective hydrogenolysis of lignin-derived aryl ethers.