(396c) Ethane Dehydroaromatization with CO2 Co-Feed over Microwave Synthesized Core-Shell Transition-Metal-Carbide@ZSM-5 Material

The continuous demand for cleaner fuel alternatives drives the world’s search for substitute fuel sources. Natural gas has been a promising fuel source and currently makes up a large portion of the North American energy production. The conversion of natural gas to value-added chemicals, typically involves the indirect production of synthesis gas (syngas) as an intermediate before the production of the desired product. Steam reforming and partial oxidation are two of the most common indirect methods of natural gas conversion. Both involve the intermediate synthesis of syngas, which is both energy and capital-intensive. Alternatively, the direct conversion of light alkanes, such as methane and ethane, into aromatics eliminates the expensive intermediate production of syngas and reduces greenhouse gas emissions. Although the conversion of natural gas by the direct method shows promise as a cost-efficient approach, the commercialization of this process faces some key technical challenges. Rapid catalyst deactivation, low selectivity to desired products, and long regeneration times are the current challenges preventing the commercialization of dehydroaromatization (DHA). The accumulation of carbon on the catalyst surface, with time on stream (TOS), can block the active sites resulting in a decrease in the selectivity and deactivation of the catalyst over time. Regeneration of the catalyst is typically carried out in oxidative atmospheres, where an exothermic reaction burns the coke off the catalyst thus producing CO₂. The addition of oxygen species, such as O₂, CO, and/or CO₂ to the inlet gas as a co-feed or pulse would help to avoid this rapid deactivation of the catalyst.

The use of CO₂ as a soft oxidant for ODHE and ODHA comes with several advantages which consist of reduced coke formation, prevention of over oxidation of metal catalyst, and through the enhanced equilibrium conversion obtained due to the removal of hydrogen via the water gas shift mechanism. Also, the use of CO₂ as an oxidant can have tremendous impacts on CO₂ emissions by consuming CO₂ and producing CO and H₂O. In this work, a core-shell particle with a transition metal carbide core and a zeolitic shell, H-ZSM-5, was synthesized using a microwave synthesis unit for the tandem ethane aromatization and dehydrogenation with CO₂ as the oxidant. The use of ethane allows for both the simultaneous reactions of ODHE and DHA at temperatures of 600°C. The DHA catalyst support, ZSM-5, was synthesized via microwave irradiation and metal promoters used consist of Mo, Fe, Ga, and Pt. The transition metal carbide catalyst core, TiC or Mo₂C, promotes the formation of ethylene, the increased ethylene concentration along with the production of CO from CO₂ can allow for the more efficient production of aromatic. Using CO₂ as a soft oxidant could also allow for extended reaction times.