Defect engineering of zinc-modified ZSM-5 zeolite catalysts for efficient aromatic synthesis from ethane and CO2

Direct synthesis of aromatics from ethane and CO 2 using bifunctional catalysts composed of Zn and zeolite has drawn considerable interest in both academia and industry. Although a lot of research has explored the influence of Zn states on aromatization, the impact of zeolite defect structure on activity is still a black box. In this study, the distribution of Si and Al within the zeolite framework was precisely generated and tailored using post-treatment methods. A comprehensive set of characterization techniques, including XRD, SEM, nitrogen adsorption–desorption, MAS NMR, CP/MAS NMR, OH-FTIR, Py-IR, NH 3 -TPD, UV–vis DRS, XPS, and TG-MS, was employed to determine the structural changes. Our studies revealed that the active Si–OH sites could be effectively eliminated by the two-step alkali treatment. The chemical shielding of active Si–OH sites played a pivotal role in preserving the [Zn(OH)] + sites, which was crucial for the activation of ethane and CO 2 . The synergistic effect of Zn and Brønsted acid sites in zeolites catalyzing dehydroaromatization could be suppressed by the formation of [ZnO x ] 2+ sites within the zeolite. Notably, a high aromatics space–time yield of 3.3 mmol aromatics /g cat /h was achieved at 570 ℃ with a time on stream of 720 min on the Zn/ATH-0.1 catalyst, due to the joint contributions of Zn and Brønsted acid sites. We demonstrated the formation of Al pairs through the unique treatment, which subsequently served as key sites for regulating aromatics selectivity. These findings offer new insights into zeolite engineering, highlighting the importance of controlling Si–OH sites distribution for enhancing CO 2 -assisted ethane aromatization.