Influence of Various Types of Zeolitic Supports on Catalytic Properties and Performance of Cr-Based Nanocatalysts Used in C2H6/CO2 Oxidative Dehydrogenation Process

In this study, the applicability of zeolitic supports and effect of zeolitic supports on catalytic properties and performance of Cr-based nanocatalysts used in oxidative dehydrogenation of ethane with CO2 were investigated. In this regard, a series of chromium oxide-based catalysts containing 3.4 wt.% of Cr were prepared by incipient wetness impregnation of clinoptilolite, SAPO-34 and HZSM-5 chosen among the natural zeolites, zeo-type materials and synthetic zeolites, respectively. To this aim, clinoptilolite was purchased and SAPO-34 and HZSM-5 were successfully synthesized via the hydrothermal method as evidenced by XRD, FESEM, BET and EDX techniques. The formation of fewer agglomerations and better dispersion of surface nanoparticles over cubic-like particles of ZSM-5 compared to other zeolitic supports were
confirmed by FESEM images. The TPD-NH3 results revealed that more desirable acidic properties were obtained by employing clinoptilolite compared to other zeolitic supports, resulting in high stability. Based on the EDX results, a higher dispersion of chromium species could be achieved using synthetic supports especially HZSM-5 due to their much higher specific surface area. This reflects in the higher content of redox Cr species stabilized in comparison with SAPO-34 and clinoptilolite, which alongside homogenous and fine surface nanoparticles and fewer agglomerations account for the superior catalytic performance of Cr/ZSM-5. Based on the characterization results, the low surface area of clinoptilolite and low dispersion of Cr species in Cr/Clinoptilolite and surface coverage and micropore blockage in Cr/SAPO-34 are mainly responsible for low ethylene yield of this catalyst compared with implementing ZSM-5 support. It was found that Cr/ZSM5 effectively dehydrogenated ethane to ethylene in the presence of CO2 at 700 °C, giving 45.4% ethylene yield. Coke deposition as a result of the presence of strong acid sites is mainly responsible for decreasing trend observed for catalytic performance with increasing reaction time.