Influence of Si/Al ratio on topological structure of twelve-membered ring zeolite and its CO₂ adsorption performance

In response to the negative effects of greenhouse gas emissions, CO₂ capture technologies are increasingly emphasized. Due to low energy consumption and operational simplicity, solid adsorption processes are regarded as promising candidates for next-generation technologies, which means that solid adsorbent has become the technical key of this process. Twelve-membered ring pore zeolites show great application potential in the field of gas separation due to their high mass transfer efficiency and high selectivity. Since the one-dimensional twelve-membered ring pores of ECR-1 and MOR zeolites have similar structural units, so by adjusting the raw material Si/Al ratio and super alkalinity, the transition between the two crystal phases and morphological changes can be achieved. The changes are verified by XRD, SEM and TEM methods. Slurry crystallization, a new preparation route, prepared a fibrous ECR-1 structure under the conditions of an over alkalinity of 0.33 and a Si/Al ratio of 7. On this basis, further increasing the Si/Al ratio can successfully synthesize MOR zeolite fiber rods with a diameter of 60-100 nm and a specific surface area of 425.58 m²/g. As the Si/Al ratio further increases, the sample becomes granular. In dynamic CO₂ adsorption tests, the CO₂ adsorption capacity of ECR-1 is observed to reach 3.98 mmol/g at 298 K and 1 bar. Furthermore, considering the actual working conditions of flue gas adsorption, adsorption tests are conducted using simulated flue gas containing water. It is found that compared with dry conditions, the CO₂ adsorption capacity of fibrous zeolite decreased by 15%, and the MOR granules decreased by 4%~5%, indicating that the fibrous zeolite is more sensitive to the influence of water vapor. The inhibitory effect of H₂O on CO₂ adsorption is investigated by combining Si/Al ratio and morphology factors, indicating that the exposed 8-membered ring channels of the fibrous morphology may be the main factor for the decrease in adsorption capacity; the stable cyclic performance of ECR-1 is also tested.