Boosting NH3-Selective Catalytic Reduction of NOx by Cooperation of Nb and Boron Nitride to V-Based Catalyst over a Wide Temperature Window

The commercialization of V-based catalysts for the selective catalytic reduction of NOx by NH3 (NH3-SCR) is hindered by their narrow operating temperature window, insufficient low-temperature (LT) activity, and severe SO2-to-SO3 oxidation. To bridge this gap, we herein introduced Nb and hexagonal BN into a VW/TiO2 system to simultaneously enhance its LT SCR activity, suppress undesired side reactions, and improve durability. Nb incorporation promoted V5+/V4+ redox cycling and enhanced lattice oxygen mobility, thus reducing the apparent activation energy and suppressing SO2 oxidation at elevated temperatures. However, excessive Nb loading induced NH3 oxidation and N2O formation. This drawback was mitigated by introducing BN as a dispersion promoter, which helped secure high catalytic performance at a reduced Nb content. The VWNb/Ti-BN catalyst achieved superior NOx conversion and N2 selectivity over a wide temperature range and benefited from notably suppressed NH3 oxidation and SO2-to-SO3 oxidation. Kinetic analysis revealed that Nb primarily lowered the reaction energy barrier via redox property enhancement, whereas BN accelerated surface reaction turnover by stabilizing and dispersing active acidic sites, markedly increasing the turnover frequency without reducing the activation energy. In situ spectroscopic analysis confirmed the accelerated consumption of adsorbed NH3 species and enhanced formation of reactive NOx intermediates, indicating SCR pathway enhancement. After aging in the presence of SO2 and H2O, the best-performing honeycomb-type monolithic catalyst retained and NOx conversion of >80%, demonstrating excellent long-term durability under practical conditions. A composition-aware machine learning model based on log-ratio-transformed variables quantitatively identified the synergistic balance among V, Nb, W, BN, and TiO2 as the dominant factor governing LT SCR performance. Thus, this work provides valuable mechanistic insights and a strategy for designing wide-temperature-window SCR catalysts with improved activity, selectivity, and resistance to sulfur poisoning.