Site-Engineered MnGa@In-CHA OXZEO Catalysts for Synergistic Methane and Nitrogen Oxides Abatement

The rapid growth of natural-gas vehicles (NGVs) necessitates robust catalysts for the simultaneous abatement of methane (CH₄), nitrogen oxides (NOx), and carbon monoxide (CO) under fluctuating exhaust compositions. We reported a site-engineered MnGa@In-CHA OXZEO catalyst in which indium was confined within an SSZ-13 framework, and Ga₂O₃ and Mn₂O₃ phases were uniformly dispersed on its exterior. Mn₂O₃ markedly enhanced redox capacity, driving NO → NO₂ oxidation and lowering the activation energy for C-H bond cleavage in CH₄, while Ga₂O₃ tuned the Brønsted acidity and mediated electron transfer among In, Mn, and Ga centers. In situ DRIFTS studies identified CH₄ activation at InO⁺ sites as the rate-determining step and revealed key intermediates (CH₃NO₂) that bridged the NOx reduction and CH₄/CO oxidation pathways. The optimal Mn₁Ga₁@In-CHA achieved ≥90% NOx conversion at 390 °C, CH₄ conversion at 495 °C, and complete CO oxidation at 300 °C under both lean and rich conditions. It also maintained high activity after 24 h in a humid feed and exhibited stable performance across a wide range of O₂ concentrations. These combined features─high activity, selectivity, stability, and adaptability─underscore the promise of MnGa@In-CHA catalysts for NGVs exhaust abatement and offer an important design strategy for multifunctional emission-control materials.