Recent advances in modelling and experimental studies of SCR catalysts in ammonia-fuelled engine applications

Ammonia (NH3) has emerged as a promising carbon-free fuel for decarbonising internal combustion engines and power systems. However, its combustion produces elevated nitrogen oxide (NOx) emissions and ammonia slip, requiring effective exhaust aftertreatment. Selective catalytic reduction (SCR) is the leading technology for NOx control, but its application to ammonia-fuelled engines presents unique challenges, including NH3-rich exhaust, variable NO2:NOx ratios, low exhaust gas temperatures (EGT), high water-vapour concentrations, and increased potential for nitrous oxide (N2O) formation. This review critically examines recent advances in SCR catalyst development and modelling for ammonia-combustion exhaust treatment. The performance of vanadia-based catalysts, transition metal oxides, and Cu- and Fe-exchanged zeolites (CuZ and FeZ) is evaluated in terms of activity, selectivity, durability, and resistance to deactivation under ammonia-rich conditions. Current understanding of NH3-SCR reaction mechanisms, catalyst ageing, and N2O formation is discussed alongside advances in microkinetic, reactor-scale, and computational fluid dynamics (CFD) modelling. Particular emphasis is placed on the strong coupling between combustion and aftertreatment, arising from the dual role of NH3 as both fuel and reductant, and the need to integrate experimental observations with predictive modelling. Finally, key research priorities are identified, including catalyst development for NH3-rich exhaust, realistic experimental validation, improved prediction of N2O emissions, and integrated combustion–aftertreatment optimisation to enable efficient, low-emission NH3-fuelled power and propulsion systems.