NOx emissions from the energy and transport sectors represent a major hazard to human health and this has been the focus of significant industrial and academic research. One important process in emissions control from vehicles is the selective catalytic reduction reaction (SCR), in which a reductant such as ammonia is injected into the exhaust to reduce the NO and NO2 (NOx) to harmless nitrogen. Copper combined with small pore zeolite materials has been shown to be very effective, but there is much still to understand about the mechanism. With greater understanding it is hoped that more effective catalysts can be designed. Here we will use TOSCA to characterise adsorbed ammonium and nitrate species in the zeolite structure.