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

Ammonia (NH 3 ) has emerged as a promising carbon-free fuel for decarbonising internal combustion engines and power systems. However, its combustion produces elevated nitrogen oxide (NO x ) emissions and ammonia slip, requiring effective exhaust aftertreatment. Selective catalytic reduction (SCR) is the leading technology for NO x control, but its application to ammonia-fuelled engines presents unique challenges, including NH 3 -rich exhaust, variable NO 2 :NO x ratios, low exhaust gas temperatures (EGT), high water-vapour concentrations, and increased potential for nitrous oxide (N 2 O) 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 NH 3 -SCR reaction mechanisms, catalyst ageing, and N 2 O 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 NH 3 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 NH 3 -rich exhaust, realistic experimental validation, improved prediction of N 2 O emissions, and integrated combustion–aftertreatment optimisation to enable efficient, low-emission NH 3 -fuelled power and propulsion systems.