Enhanced Water Resistance in Methane-Selective Catalytic Reduction of NOx over In@H-Beta/Fe2O3 Catalyst

Methane selective catalytic reduction (CH4-SCR) represents a promising strategy for nitrogen oxides (NOx) abatement, yet its practical application is hindered by catalyst deactivation in the presence of water, caused by competitive adsorption on acid sites and irreversible hydroxylation of active metal species. In this study, we developed a dual-functional In@H-Beta/Fe2O3 catalyst through sequential ion-exchange and impregnation. This architecture confines indium species within the channels of H-Beta zeolite, while Fe2O3 nanoparticles are dispersed on the external surface, creating a synergistic system featuring a hydrophobic layer and strong Fe–O–In interfacial interactions. Under 5% H2O conditions, the optimized catalyst achieves 85% NOx conversion (vs 40% for conventional In@H-Beta). The enhanced water resistance is attributed to two factors: first, Fe2O3 establishes a physical barrier that protects acid sites and stabilizes InO+ active sites via Fe–O–In bonding, thereby inhibiting hydroxylation; second, strong interfacial Fe–O–In interactions further stabilize InO+ active sites against aqueous deactivation. Additionally, the Fe2+/Fe3+ redox cycle is proposed to facilitate O2 activation. In situ DRIFTS studies under 5% H2O confirm effective CH4 activation, as indicated by markedly more intense C–H stretching bands compared with In@H-Beta. The reaction pathway involves NO activation over Brønsted acid sites to form nitrate species, and CH4 activation on InO+ sites generating methyl radicals, which subsequently participate in NOx reduction. This work offers a new design strategy for developing highly active and water-tolerant CH4-SCR catalysts suitable for industrial flue gas treatment.