Ethylene and Water Co-Adsorption on Ag/SSZ-13 Zeolites: A Theoretical Study

Zeolites are capable of selectively adsorbing molecules and therefore are applicable to chemical separation challenges. In this work, two probe molecules, ethylene (C2H4) and water (H2O) are modeled for their adsorption behavior in silver (Ag) ion-exchanged SSZ-13 zeolite (Si/Al = 11). A microkinetic model was constructed to include adsorbate-adsorbate effects due to multiple adsorption on individual active sites. As a basis for comparison, adsorption fractions were also predicted with the classical Langmuir competitive adsorption. Density functional theory (DFT) calculations were conducted, with 3 functionals to explore uncertainties, and up to three adsorbed molecules per Ag active site were investigated. When the DFT energies were passed to the adsorption models, the highest probability adsorption fraction prediction was for ethylene adsorption dominating water adsorption. An exception was that the Heyd-Scuseria-Ernzerhof functional energies passed to the Langmuir model predicted greater water adsorption than ethylene adsorption. The change in adsorption fractions as a function of shifting C2H4 feed gas concentration are reported.