Screening of Adsorbent/Catalyst Composite Monoliths for Carbon Capture-Utilization and Ethylene Production

Combining CO2 adsorption and utilization in oxidative dehydrogenation of ethane (ODHE) into a single bed is an exciting way of converting a harmful greenhouse gas into marketable commodity chemicals while reducing energy requirements from two-bed processes. However, novel materials should be developed for this purpose because most adsorbents are incapable of capturing CO2 at the temperatures required for ODHE reactions. Some progress has been made in this area; however, previously reported dual-functional materials (DFMs) have always been powdered-state composites and no efforts have been made toward forming these materials into practical contactors. In this study, we report the first-generation of structured DFM adsorbent/catalyst monoliths for combined CO2 capture and ODHE utilization. Specifically, we formulated M-CaO/ZSM-5 monoliths (M = In, Ce, Cr, or Mo oxides) by 3D-printing inks with CaCO3 (CaO precursor), insoluble metal oxides, and ZSM-5. The physiochemical properties of the monoliths were vigorously characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), N2 physisorption, elemental mapping, pyridine Fourier transform infrared spectroscopy (Py-FTIR), H2-temperature-programmed reduction (H2-TPR), and NH3-temperature-programmed desorption (NH3-TPD). Their performances for combined CO2 adsorption at 600 °C and ODHE reaction at 700 °C under 25 mL/min of 7% C2H6 were then investigated. The combined adsorption/catalysis experiments revealed the best performance in Cr-CaO/ZSM-5, which achieved 56% CO2 conversion, 91.2% C2H4 selectivity, and 33.8% C2H4 yield. This exceptional performance, which was improved from powdered-state DFMs, was attributed to the high acidity and numerous oxidation states of the Cr2O3 dopant which were verified by NH3-TPD and H2-TPR. Overall, this study reports the first-ever proof-of-concept for 3D-printed DFM adsorbent/catalyst materials and furthers the area of CO2 capture and ODHE utilization by providing a simple pathway to structure these composites.