Exploring cation gating in RHO zeolites via modification of Cs+/Na+ Ratio: Analysis of sorption isotherms for carbon dioxide, hydrogen, methane, and nitrogen

The temperature-regulated gated adsorption behaviour of Na, Cs-RHO zeolites with varying Cs + /Na + mass ratios (2.2, 1.0, and 0.6) was investigated for H 2 , CO 2 , N 2 , and CH 4 at pressures up to 800 kPa and temperatures from 77.15 to 413.15 K. Zeolite RHO 2.2 exhibited a "trapdoor" effect, where adsorption was negligible at low temperatures but significantly increased above a critical temperature, particularly for H 2 , CO 2 , and N 2 . This behaviour is attributed to Cs + cations dynamically blocking or opening the pore windows, regulating gas access. In contrast, RHO 1 and RHO 0.6 followed typical physisorption without gating effects, with RHO 0.6 showing the highest CO 2 , CH 4 , and N 2 adsorption in the order CO 2 > CH 4 > N 2 . The separation potential of zeolite RHO 2.2, 1, and 0.6 for CO 2 /N 2 , and CO 2 /CH 4 gas mixtures was evaluated by determining the pure gas adsorption capacities. Ideal Adsorbed Solution Theory (IAST) estimated the adsorption selectivity across different conditions. The negligible CH 4 uptake by RHO 2.2 highlights its high CO 2 /CH 4 selectivity, making it a strong candidate for CO 2 separation in biogas and natural gas purification. These findings provide new insights into temperature-controlled adsorption in zeolites and the tunability of gas selectivity through cation exchange. • The adsorption of H 2 , CO 2 , N 2 , and CH 4 in zeolite RHO with different Cs + /Na + mass ratios were examined for the gating effect. • Zeolite RHO 2.2 with a higher Cs + /Na + mass ratio exhibits a temperature-dependent adsorption behavior for H 2 , CO 2 , and N 2 . • Zeolite RHO 2.2 is a promising PSA adsorbent for the separation of CO 2 / CH 4 gas mixtures. • zeolites RHO 0.6 with a lower Cs + /Na + mass ratio show the highest uptake H 2 , N 2 , and CH 4 capacity.