H2/CH4 Competitive Adsorption of LTA Zeolite: Effects of Cations, Si/Al Ratio, Adsorption Temperature, and Pressure

The efficient separation of H2 from CH4 is crucial for hydrogen purification from industrial off-gases using pressure swing adsorption (PSA). In this study, the competitive adsorption behavior of H2/CH4 on LTA zeolites was systematically investigated via grand canonical Monte Carlo (GCMC) simulations, with a focus on the effects of cation type (Na+, Li+, Ca2+, Mg2+), Si/Al ratio (1–1.5), temperature (298–318 K), and pressure (0.2–2 MPa). The results reveal that CH4 favors β-cages as excellent adsorption sites with high population density, followed by the regions adjacent to the cations or framework oxygen atoms of the eight-membered rings. In contrast, H2 is uniformly distributed throughout all the channels. Cations with higher valence and smaller ionic radii (e.g., Mg2+) enhance CH4 adsorption capacity and diffusion more effectively than monovalent or larger cations. Increasing the Si/Al ratio reduces cation content and exposes more framework oxygen atoms, particularly those in Si–O–Si environments, which improve CH4 adsorption. Elevated temperature weakens CH4 adsorption while promoting H2 diffusion and pore occupancy. Although higher pressure increases the uptake of both gases, H2 adsorption rises more substantially and distributes more widely, leading to a decrease in CH4/H2 selectivity.