Structured Bifunctional Catalysts for CO2 Activation and Oxidative Dehydrogenation of Propane

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The direct ink writing of metal oxide/ZSM-5 inks has been developed and is used to structure bifunctional catalysts for CO 2 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 % Ga 2 O 3 /ZSM-5, (iii) 1.3 wt % Ga 2 O 3 –1.3 wt % V 2 O 5 –1.3 wt % ZrO 2 /ZSM-5, (iv) 0.7 wt % Cr 2 O 3 –1.1 wt % Ga 2 O 3 –1.1 wt % V 2 O 5 –1.1 wt % ZrO 2 /ZSM-5, (v) 2 wt % Ga 2 O 3 –2 wt % V 2 O 5 /ZSM-5, and (vi) 1 wt % Cr 2 O 3 –1.5 wt % Ga 2 O 3 –1.5 wt % V 2 O 5 /ZSM-5 have been synthesized and characterized by N 2 physisorption, X-ray diffraction, X-ray fluorescence, H 2 -TPR, and NH 3 -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 CO 2 as a soft oxidant for oxidative dehydrogenation of propane (ODHP) to produce propylene at 550 °C and space velocity of 4500 mL/g cat ·h for 6 h time-on-stream. The CO 2 -ODHP experiments with CO 2 revealed the best performance over 2 wt % Ga 2 O 3 –2 wt % V 2 O 5 /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 CO 2 and minimal deactivation after 6 h when CO 2 was present, but displayed varying degrees of deactivation when CO 2 was absent. Effectively, these results signified the importance of CO 2 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.