(624e) CO2-Assisted Ethane Dehydroaromatization: Investigation of Metal and Support Influence

The large supply of ethane from shale gas has increased interest on the study of its catalytic conversion to valuable products. Ethane is converted to aromatic compounds through the dehydroaromatization reaction (EDA). EDA reaction is composed of a series of reactions, been the first and limiting step the dehydrogenation of ethane to ethylene. The addition of CO₂ favors the ethane dehydrogenation, by consuming the H₂ through the reverse water gas shift reaction leading to higher ethane conversions. In addition, CO₂ reacts with solid carbon by the reverse Boudouard reaction, producing CO and avoiding catalyst deactivation by coke deposition, which is the main challenge in the development of catalysts for EDA reaction. In this study, catalysts with gallium (Ga) and zinc (Zn) over HZSM-5 were prepared, characterized, and tested in the CO₂ assisted EDA reaction.

The catalysts were prepared by wet impregnation method over HZSM-5 with different SiO₂/Al₂O₃ ratio (60, 91 and 371). The samples were calcined at 600 °C for 4 hours in 50 mL/min air flow. The catalysts were characterized by X-ray diffraction (XRD), Raman spectroscopy, temperature-programmed reduction (TPR-H₂), temperature programmed desorption of NH₃ and CO₂ (TPD-NH₃ and TPD-CO₂) and N₂ physisorption. The catalytic tests were performed in a tubular reactor with online analysis in a gas chromatograph varying parameters such as temperature, weight hourly space velocity, and C₂H₆/CO₂ feed ratio. Time-on-stream tests were then performed to assess catalyst stability.

Results showed that the Ga catalyst exhibited higher aromatics selectivity, while the Zn catalyst demonstrated greater ethane conversion and ethylene selectivity. Among Ga catalysts supported on zeolites with different SiO₂/Al₂O₃ ratios, the one with higher aluminum content (SiO₂/Al₂O₃=60) performed best, evidencing the importance of Bronsted acid sites in aromatic compound formation. Raman spectroscopy identified coke deposition in the catalysts post-reaction, indicating potential catalytic deactivation.