Electronic Modulation via Silicon Incorporation in MnSmO _<i>x</i> Catalysts for Enhanced Low-Temperature NH ₃ -SCR Performance

The development of efficient low-temperature selective catalytic reduction (SCR) catalysts for nitrogen oxide (NOx) removal remains a critical challenge in environmental catalysis. The enhancement of electron transfer through optimized synergy between paired active sites presents a promising strategy for developing SCR catalysts with high catalytic activity across a broad temperature range. Herein, a series of novel Si-modified MnSmOx catalysts were synthesized via the Stöber method, which achieves >90% NOx conversion between 150–247 °C, while Mn4SmOx catalyst did not exceed 90% NOx conversion over the entire test temperature range. According to the experimental and theoretical studies, which can demonstrate that Si acts as a dual-functional promoter: (i) structurally, it creates spherical particle stacking, increasing the surface area by 3.2 times (144.8 vs 45.4 m2 g–1) and exposing more active sites; (ii) electronically, it modulates the valence states of Mn (Mn4+ ↑54.1% vs 22.6%) and Sm (Sm3+ ↑77.5% vs 58.1%), and Si induces orbital hybridization between Mn 3d and Si 2p states, elevating the Mn d-band center (−2.43 vs – 2.84 eV) to strengthen gas adsorption (NH3/NO/O2 adsorption energy ↑). Crucially, Si optimizes the acid-redox balance by introducing weak/medium-strong acid sites, accelerating the rate-determining step (NH3* → NH2*+H*, with the barrier decreased by 0.55 eV) while inhibiting overoxidation (N2 selectivity ↑). The catalyst also exhibits exceptional H2O resistance (activity loss 20 ∼25 vs 35%) due to Si-stabilized active sites. This work provides a paradigm for designing high H2O-resistance vanadium-free SCR catalysts through electronic-structure engineering, offering atomic-level insights into the synergistic effects of Mn–Sm–Si triple sites.