Adsorption-Enhanced Bifunctional Catalysts for In Situ CO₂ Capture and Utilization in Propylene Production: A Proof-Of-Concept Study

In this study, cooperative bifunctional materials (BFMs)composed of combined adsorbent and catalyst materialsare synthesized and processed through additive manufacturing by 3D printing adsorbent/catalyst monoliths with a CaO adsorbent phase balanced against an M@ZSM-5 (M = In, Ce, Cr, or Mo oxide) heterogeneous catalyst phase. The adsorbent/catalyst monoliths were characterized using NH₃-TPD, H₂-TPR, N₂ physisorption, X-ray photoelectron spectroscopy, X-ray diffraction, pyridine-Fourier transform infrared spectroscopy, C₃H₈-diffuse reflectance infrared Fourier transform spectroscopy, and energy-dispersive spectroscopy. Their performances were evaluated for combined CO₂ capture and propane dehydrogenation at 600–700 °C. These experiments revealed that a reaction temperature of 600 °C generates the best performance for all samples due to the shift toward thermal cracking at higher temperatures. Moreover, 600 °C was usable for both CO₂ adsorption and catalysis, so the materials reported here could truly perform both adsorption and catalysis isothermally. Of the materials, CaO-Mo@ZSM-5 displayed the best performance, generating 20.4% propylene yield, 20% propane conversion, 75% CO₂ conversion, and 5.4 mmol/g CO₂ capture capacity at 600 °C. The stability of this sample was then assessed across ten adsorption/reaction cycles at T = 600 °C, where its propane conversion, CO₂ conversion, and propylene yield varied by less than 5% across the entirety of the experiment. Overall, this work accomplishes three key goals: it (i) expands the concept of BFM materials to a previously unexplored reaction for direct CO₂ capture from air (direct air capture) or flue gas, and subsequent utilization, (ii) provides a facile way of structuring BFM materials into practical contactors, and (iii) allows adsorption and catalysis to occur at the same temperature with high cyclic stability within a single bed.