Metal-free carbon catalyst with nitrogen dopant and vacancy site achieving 100 % NO_x conversion: a synergistic promotional mechanism for the fast NH₃-SCR reaction

Low-temperature selective catalytic reduction of NO_x using NH₃ (NH₃-SCR) over metal-free carbon catalysts significantly relies on the precise engineering of active sites. Although heteroatom dopants have been proven to be active sites, the effects of intrinsic defects in carbon catalysts and their coupling with heteroatoms on the NH₃-SCR pathway are still unclear. Here, we demonstrate a novel approach to boosting NH₃-SCR through the synergy between nitrogen dopants and vacancies, achieved by preparing carbon catalysts with controllable nitrogen-doping and vacancy sites. The introduction of enriched vacancies and nitrogen dopants by a microwave-induced co-activation method provides a superior NO_x conversion (100 % at 180 °C) and good sulfur resistance. Density functional theory (DFT) calculations further unlock the coupling effects of nitrogen dopants and vacancies, that vacancies can not only distort the carbon basal plane and redistribute charges, thereby enhancing O₂ activation, but also activate the originally inert pyridine nitrogen and synergistically enhance O₂ activation. In this way, NO oxidation to NO₂ can be promoted, further enabling the occurrence of the fast NH₃-SCR pathways (NO + NO₂ + 2NH₃ → 2N₂ + 3H₂O), which is crucial for improving the efficiency of NO_x removal. This work provides new perspectives on the role of vacancies in carbon-catalyzed reactions, guiding the design of high-performance carbon catalysts for cost-effective NO_x removal.