Confining FeO x Nanoclusters within the ZSM-5 Framework Suppresses NH ₃ Over-Oxidation for High-Temperature SCR

Framework-incorporated metal species in zeolites are extensively investigated for selective catalytic reduction (SCR) due to their spatial confinement and tunable coordination environments, while their mechanisms for suppressing parasitic NH 3 oxidation remain to be elucidated. Herein, we construct three systems of Fe-incorporated ZSM-5 catalysts (In-situ x Fe@Z, x = 0.05, 0.1, 0.5, and 3) via the “ship-in-a-bottle” strategy, corresponding to isolated framework Fe sites, mixed framework and extra-framework Fe species, and predominantly extra-framework Fe nanoclusters. The In-situ 0.5Fe@Z catalyst exhibits NO conversion of 89.5–95.1% at 500–850 °C and maintains stability for over 120 h in the presence of SO 2 and water vapor. Theoretical calculations reveal that low-coordination framework Fe sites create a spatially confined environment that selectively promotes NH 3 activation while elevating the energy barrier for progressive NH 2 * dehydrogenation, suppressing the formation of highly reactive NH * and N * radicals. The spatially confined Fe O x nanoclusters located within the zeolite framework are identified as the dominant active sites for the high-temperature SCR performance. This work provides fundamental insights into the rational design of framework metal-zeolites for achieving wide-temperature-range deNO x with high N 2 selectivity.