Reducing Methane Emissions for Marine Engine Applications: Accelerated CH4 Oxidation by NO on a Fe-BEA Zeolite

Abstract Methane emissions from liquefied natural gas (LNG)-powered marine engines pose a significant challenge due to methane’s high global warming potential. Conventional platinum group metal (PGM)-based methane oxidation catalysts suffer from poor sulfur and hydrothermal stability, limiting their applicability in marine exhaust aftertreatment systems. This study investigates a commercially available Fe-BEA zeolite as a noble-metal-free alternative for methane oxidation under realistic exhaust conditions. The catalyst demonstrates low activity in the presence of O2 and H2O alone, but the addition of NO significantly enhances CH4 conversion due to the formation of NO2. The NO/NO2 cycle acts as a cocatalyst. NO2 facilitates both CH4 and CO oxidation, improving CO2 selectivity. Pressure-dependent experiments reveal that increased space time at elevated pressures is the primary driver of enhanced conversion. Hydrothermal aging at 550 and 650 °C for 100 h does not lead to a loss in activity, while aging at 700 °C results in minor deactivation due to reduced NO oxidation capacity. Catalyst characterization via NH3-TPD, BET, and XRD confirms structural changes, including defect site healing and dealumination. These findings highlight the Fe-BEA zeolite as a stable and effective catalyst for methane abatement in harsh marine engine environments, with engine optimization and preturbo placement offering promising strategies for improved performance.