Ni/Biochar-catalyzed biomass gasification for process-compatible NOx reduction in cement pre-calciner: pathways and mechanisms

In-situ reductant generation within the cement pre-calciner is a critical requirement for achieving process-compatible denitrification (de-NO x ), as it supplies H 2 and CO to enhance established NH 3 -SNCR pathways or enable direct NO x reduction. However, conventional biomass gasification under flue gas conditions suffers from low gas yield and poor reductant selectivity, resulting in limited de-NO x efficiency and high reliance on ammonia. Herein, we address this upstream bottleneck by developing Ni catalysts supported on waste-derived activated carbon (Ni/AC) featuring highly dispersed Ni clusters and strong metal–support interactions. Under representative pre-calciner conditions, Ni/AC-catalyzed biomass gasification exhibited a 21-fold enhancement in total gas yield (from 198 mL/g to 4237 mL/g), increased H 2 and CO selectivity from 40% to 95%, and suppressed CO 2 formation from 54% to only 3%, while demonstrating high adaptability to diverse biomass feedstocks. Mechanistically, highly dispersed Ni sites promote sequential H 2 O dissociation into ·OH and ·H radicals, lowering the activation barriers for aromatic tar conversion (modeled by toluene) by 0.54 and 1.09 eV for C–H and C–C bond cleavage, respectively, thereby promoting deep tar cracking. Meanwhile, CO 2 tends to activate on Ni sites and then break the C=O bond, providing an alternative pathway for CO formation. These insights capture the dominant reaction trends governing reductant formation on Ni surfaces. Overall, this work demonstrates the efficient and selective generation of reductants via catalytic biomass gasification in cement flue gas, laying the scientific foundation for process-compatible de-NO x during clinker production.