Correlating the strength of reducing agent adsorption with Ag/Al2O3 catalyst performances in selective catalytic reduction (SCR) of NOx

NMR relaxation has been used to characterise the strength of surface interaction of reducing agent species in Ag/Al2O3 catalysts used for the selective catalytic reduction (SCR) of NOx. Several classes of compounds, including aliphatic and aromatic hydrocarbons, as well as alcohols, were investigated. The results show that the strength of interaction of the reducing agent with the catalyst surface, characterised by the NMR relaxation time ratio T1/T2, plays an important role in determining the catalyst performances, with reducing agents able to compete with water for adsorption over the surface giving better catalytic activities. In particular, a clear trend was observed when comparing the T1/T2 ratio of different reducing agents with the initial activity of the catalyst, in particular with the activation temperature, with species such as alcohols, which showed a higher affinity with the catalyst, showing an easier initial activation. Whilst SCR is a complex reaction, whereby a series of phenomena are responsible for the overall catalytic activity, the strength of surface interaction of the reducing agent is a useful indicator for the initial catalytic activation in such processes.