Synthesis of Ga, Zr, V, and Cr ‑Doped 3D-Printed ZSM‑5 Monoliths and Their Catalytic Performance for Selective Dehydrogenation of Propane in the Presence and Absence of CO2

Researchers have considered CO₂ as a mild oxidant that can overcome over-oxidation and low propylene selectivity that are typically associated with the current synthesis routes. Oxidative dehydrogenation of propane to propylene with CO₂ (ODPC) is an attractive method for catalytic method for propylene production compared to oxidative dehydrogenation with oxygen (ODHE), as it manufactures a valuable product and mitigates anthropogenic emissions.^1,2 Herein, we report the rapid synthesis of customized metal-doped zeolite monoliths with various compositions and hierarchical porosity (macro-meso-micro) by 3D printing. To enhance catalytic activity and propylene selectivity in OPDC, single- and mixed metal oxide of Ga, Zr, V, and Cr (5-35 wt.%) were synthesized by directly incorporated commercial oxides into the printing pastes. The monoliths’ physical and chemical characteristics were studied through XRD, N₂ physisorption, FTIR, SEM-EDS, CO₂-DRIFTS, H₂-TPR, and NH₃-TPD. Their performances were evaluated for OPDC at 500-650 °C for 6 h of reaction time. The reaction experiments revealed that the vanadium-containing samples exhibited the best performance, where 40% propane conversion and 97% propylene selectivity were observed in the presence of CO₂. Moreover, the monoliths produced by direct oxide printing did not produce any BTX and showed less than 2% coking after 6 h reaction time. Because of these properties, this new method of direct printing was concluded to be superior to pre-dissolution of nitrate salts for the production of catalytic monoliths. Overall, this study represents a novel way of manufacturing structured catalysts and demonstrates materials which outperform the state-of-art for ODPC propane conversion.

References

[1] M.A. Atanga et al. Oxidative dehydrogenation of propane to propylene with carbon dioxide, Appl. Catal. B Environ. 220 (2018) 429–445.

[2] F. Magzoub et al. 3D-printed ZSM-5 monoliths with metal dopants for methanol conversion in the presence and absence of carbon dioxide, Appl. Catal. B Environ. 245 (2019) 486–495.