The effect of cations on the ammonia synthesis reaction under the confinement in FAU zeolites

Abstract

We performed Monte Carlo molecular simulations in RMC and GCMC ensembles, to study the impact of Na⁺ charge-balancing cations in the aluminum-substituted zeolites on the adsorption behavior of H₂, N₂, and NH₃. The adsorption isotherms were obtained for single-component gas adsorption and adsorption from the ammonia synthesis reaction mixture. Our findings indicate that the presence of Na⁺ cations in zeolites alters the adsorptive characteristics of all the molecules under the study. Specifically, Na⁺ cations have a significant influence on the adsorption behavior of ammonia, effectively preventing its phase transition. Adsorption from the mixture showed that Na ⁺ cations enhanced the selectivity of ammonia adsorption over N₂, and H₂, as compared to pure-silica zeolites. Further, the impact of cations on the reaction equilibrium under the confinement of FAU zeolite was investigated. The confinement effect in ammonia production was shown to be improved due to the presence of cations. We suggest that the optimal conditions for the process can be reached at 573 K and 10 bar, providing a good value of 0.93 of ammonia mole fraction adsorbed.