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

Abstract

Using a low silica-to-alumina ratio NaZSM-5 zeolite as the support, a bimetallic modified catalyst, GaxZnZ5, was prepared through ion-exchange method for CO2-mediated oxidative dehydrogenation of C2H6 (CO2-ODH). Based on systematic characterization and evaluation, it was found that Zn is the primary active component in the catalytic system for activating C2H6, but it is merely active towards CO2, leading to rapid catalyst deactivation. Under the influence of Ga species, CO2 can readily engage into the reaction network. During the initial stage of the reaction, the activated CO2 primarily participants in dry reforming with C2H6-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, CO2 becomes involved in the reaction through the reverse water-gas shift (RWGS) reaction and carbon elimination reactions, thereby shifting the reaction equilibrium towards C2H4 formation while alleviating the accumulation of carbon deposition and thus enhancing stability. With the optimum catalyst (Ga0.27ZnZ5), excellent and stable performance with 22.64 % C2H4 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.

Keywords

• Catalysts
• Oxidative dehydrogenation of ethane
• Stability
• CO2 activation