Enhanced Water Resistance in Methane-Selective Catalytic Reduction of NO x over In@H-Beta/Fe 2 O 3 Catalyst

Methane selective catalytic reduction (CH 4 -SCR) represents a promising strategy for nitrogen oxides (NO x ) 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/Fe 2 O 3 catalyst through sequential ion-exchange and impregnation. This architecture confines indium species within the channels of H-Beta zeolite, while Fe 2 O 3 nanoparticles are dispersed on the external surface, creating a synergistic system featuring a hydrophobic layer and strong Fe–O–In interfacial interactions. Under 5% H 2 O conditions, the optimized catalyst achieves 85% NO x conversion (vs 40% for conventional In@H-Beta). The enhanced water resistance is attributed to two factors: first, Fe 2 O 3 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 Fe 2+ /Fe 3+ redox cycle is proposed to facilitate O 2 activation. In situ DRIFTS studies under 5% H 2 O confirm effective CH 4 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 CH 4 activation on InO + sites generating methyl radicals, which subsequently participate in NO x reduction. This work offers a new design strategy for developing highly active and water-tolerant CH 4 -SCR catalysts suitable for industrial flue gas treatment.