Effect of Ga doping on the catalytic performance of Zn-ZSM-5 for CO2-assisted oxidative dehydrogenation of C2H6

Using a low silica-to-alumina ratio NaZSM-5 zeolite as the support, a bimetallic modified catalyst, Ga x ZnZ5, was prepared through ion-exchange method for CO 2 -mediated oxidative dehydrogenation of C 2 H 6 (CO 2 -ODH). Based on systematic characterization and evaluation, it was found that Zn is the primary active component in the catalytic system for activating C 2 H 6 , but it is merely active towards CO 2 , leading to rapid catalyst deactivation. Under the influence of Ga species, CO 2 can readily engage into the reaction network. During the initial stage of the reaction, the activated CO 2 primarily participants in dry reforming with C 2 H 6-x species that rapidly formed on highly active Zn sites. However, the rapid cleavage of C-H bonds on these Zn sites leads to significant carbon deposition and subsequent deactivation. Following this rapid deactivation phase, CO 2 becomes involved in the reaction through the reverse water-gas shift (RWGS) reaction and carbon elimination reactions, thereby shifting the reaction equilibrium towards C 2 H 4 formation while alleviating the accumulation of carbon deposition and thus enhancing stability. With the optimum catalyst (Ga 0.27 ZnZ5), excellent and stable performance with 22.64 % C 2 H 4 yield and nearly 100 % selectivity could be achieved after an induction period of ca. 100 minutes, these are among the highest values reported so far. • Zn is the primary active component in the catalytic system for activating C 2 H 6 . • Ga can effectively activate CO 2 and improve the catalysts' stability. • CO 2 is mainly involved in RWGS reaction and carbon elimination reaction. • Ga 0.27 ZnZ5 catalyst demonstrated the highest stability.