Structured Bifunctional Catalysts for CO₂ Activation and Oxidative Dehydrogenation of Propane

The direct ink writing of metal oxide/ZSM-5 inks has been developed and is used to structure bifunctional catalysts for CO2 reduction in tandem with propane dehydrogenation. The structured catalysts of (i) H-ZSM-5 (with two different Si/Al ratios of 50 and 280), (ii) 4 wt % Ga2O3/ZSM-5, (iii) 1.3 wt % Ga2O3-1.3 wt % V2O5-1.3 wt % ZrO2/ZSM-5, (iv) 0.7 wt % Cr2O3-1.1 wt % Ga2O3-1.1 wt % V2O5-1.1 wt % ZrO2/ZSM-5, (v) 2 wt % Ga2O3-2 wt % V2O5/ZSM-5, and (vi) 1 wt % Cr2O3-1.5 wt % Ga2O3-1.5 wt % V2O5/ZSM-5 have been synthesized and characterized by N2 physisorption, X-ray diffraction, X-ray fluorescence, H2-TPR, and NH3-TPD. The structured bifunctional catalysts have microporous, mesoporous, and macroporous structures that generate a higher specific surface area and enhanced molecular mass transfer of reactants and products from the active sites. A fixed bed reactor was used to assess the effects of structuring bifunctional catalysts on a process that uses CO2 as a soft oxidant for oxidative dehydrogenation of propane (ODHP) to produce propylene at 550 °C and space velocity of 4500 mL/gcat·h for 6 h time-on-stream. The CO2-ODHP experiments with CO2 revealed the best performance over 2 wt % Ga2O3-2 wt % V2O5/ZSM-5, which achieved 35% propane conversion and 94% propylene selectivity. Also, it is worth noting that all structured bifunctional catalysts showed zero production of BTX both with and without CO2 and minimal deactivation after 6 h when CO2 was present, but displayed varying degrees of deactivation when CO2 was absent. Effectively, these results signified the importance of CO2 as an oxidant over these materials, as they mitigated coke formation and led to exceptional long-term stabilities. Overall, this study reports a new formulation of directly printed oxide/ZSM-5 structured bifunctional catalysts and provides a deeper understanding of the exciting materials generated by this new method