Developing a Thermodynamic Model for the Interactions between Water and Cu in the Zeolite SSZ-13

The Cu-exchanged zeolite SSZ-13 is an efficient catalyst in the selective catalytic reduction of nitrous oxides in the presence of ammonia, and understanding the nature of the active sites under realistic conditions is important in rationalizing its activity. Especially the interactions between Cu and water have drawn significant amounts of attention in recent years. In this work we develop a thermodynamic model for the water coordination of Cu based on static calculations and present occupational probabilities and phase diagrams for different Al distributions at different temperatures and water pressures. We find that only at high temperatures and low pressures is the bare Cu cation the most stable species and that the cation is solvated at lower temperatures and higher pressures. In the following we compare our results to experimental and theoretical work in this field and find good agreement. This work shows that it is possible to construct an accurate thermodynamic model for water interactions with Cu in zeolites and it will be interesting to see how a similar methodology can be applied to elucidate different problems in the future.