​Air pollution from road vehicles has damaging health and environmental effects. The Selective Catalytic Reduction (SCR) reaction can convert harmful NOx gases to nitrogen gas and water, and often uses ammonia with metal exchanged zeolite catalysts. Researchers measured the diffusion of ammonia across a commercial copper-chabazite (Cu-CHA) zeolite catalyst, and compared it with measurements in H-CHA. They used quasielastic neutron scattering (QENS) on OSIRIS to look at the effect of counterion presence. Their results, published in Physical Chemistry Chemical Physics, showed similar rates and activation energies of diffusion for both systems, suggesting that the presence of counterions has little impact on the diffusion of ammonia. Molecular dynamics simulations showed that strong coordination of NH3 with Cu2+ counterions in the centre of the chabazite cage shielded other molecules from interaction with the ion, allowing diffusion through the windows of the chabazite structure to continue freely.

Related publication: A. J. O'Malley et al. “Ammonia mobility in chabazite: insight into the diffusion component of the NH3 -SCR process" Phys. Chem. Chem. Phys., 18 (2016), 17159-17168 

​DOI: 10.1039/C6CP01160H