(57b) CO2-Assisted Oxidative Dehydrogenation of Alkanes on Supported Mo2c Catalysts

Conventional methods for light olefin production, such as steam cracking or dehydrogenation, are energetically expensive. Oxidative dehydrogenation (ODH) of light alkanes is a suitable alternative, though unselective overoxidation limits its use. Using CO₂ as an oxidant in ODH suppresses the over oxidation of products, improving product selectivity. Design of suitable catalysts with high activity and selectivity and resistance to coking pose challenges in the application of this process. Molybdenum carbide (Mo₂C) is a potential candidate for CO₂-ODH due to its high activity for CO₂ activation and alkane dehydrogenation. The catalytic performance of Mo₂C is dependent on pre-treatment methods, reaction conditions, and the support and promoters used. The addition of support materials influences the acid and base prop­erties of the catalyst surface, which can affect CO₂ and alkane activation.

This work investigates CO₂-assisted ODH of ethane (C₂H₆) over Mo₂C and supported Mo₂C catalysts. Among various supports, SBA-15, a silica-based ordered mesoporous material, shows better activity, arguably due to the higher specific surface area, large pore diameters and low surface acidity. Unsupported and supported Mo₂C catalysts are synthesized and the role of the carburization process is investigated. The catalysts are characterized using standard techniques. CO₂-assisted C₂H₆ ODH is studied on bare (without pre-treatment) and CO₂ pre-treated catalyst surfaces. The better activity of CO₂ pre-treated catalysts indicates that an optimum oxygen coverage or an oxy-carbide surface is required for C₂H₆ and CO₂ activation on Mo₂C catalysts. The SBA-15 supported Mo₂C catalyst showed higher conversion, better stability and significant selectivity to ethylene. Detailed kinetic measurements are carried out and the role of temperatures, reactant partial pressures and co-reactants is investigated. Furthermore, mechanistic details will be analyzed with the help of operando spectroscopy and transient analyses under CO₂-ODH conditions.