(650e) Combining CO2 Reduction with Propane Oxidative Dehydrogenation over Bimetallic Catalysts

Elaine Gomez and Jingguang G. Chen*

Department of Chemical Engineering, Columbia University, New York City, NY 10027, USA

*jgchen@columbia.edu

Abstract: Propylene is one of the most diverse petrochemical building blocks used for the production of many chemicals (e.g. polypropylene, propylene oxide, and acrylonitrile). The inherent variability and insufficiencies in the co-production of propylene from steam crackers has raised concerns regarding the global propylene production gap and has directed industry to more on-purpose propylene technologies¹. The oxidative dehydrogenation of propane by CO₂ (CO₂-ODHP) can potentially fill this gap while consuming a greenhouse gas. Utilizing propane and CO₂ presents several advantages over the conventional processes of direct or O₂ assisted propane dehydrogenation, including lower operating temperatures, less coke formation, and higher equilibrium conversions.² The reactions of CO₂ with propane may occur through two distinct pathways, oxidative dehydrogenation (CO₂ + C₃H₈ → C₃H₆ + CO + H₂O) and dry reforming (3CO₂ + C₃H₈ → 6CO + 4H₂). The two reactions should occur simultaneously at temperatures around 823 K and above with considerable conversions, allowing the formation of both dehydrogenation products (propylene) and reforming products (synthesis gas). Thus, it is of great interest to identify catalytic systems that can selectively break either the C-H bond to produce propylene or the C-C bonds to produce synthesis gas (CO + H₂).

Non-precious Fe₃Ni and precious Ni₃Pt supported on CeO₂ have been identified as promising catalysts for CO₂-ODHP and dry reforming, respectively, in flow reactor studies conducted at 823 K. For oxidative dehydrogenation, nonprecious metal based Fe₃Ni had higher stability and propylene production rates. Fe₃Ni showed distinct C₃H₆ yield compared to its parent metals and the Ni₃Pt catalyst showed both greater activity and stability than the corresponding monometallics. In-situ X-ray absorption spectroscopy measurements revealed the oxidation states of metals under reaction conditions and density functional theory was utilized to identify the most favorable reaction pathways over the two types of catalysts. Additional flow reactor studies have been performed on the Fe₃Ni and Ni₃Pt bimetallic systems with other oxide supports (TiO_2, ZrO₂, SiO₂, γ-Al₂O₃, and V₂O₅) to examine the effects of strong support metal interactions, surface defects, inert surfaces, irreducibility, as well as alkane activation on both the CO₂-ODHP and DRP pathways. Overall, two types of bimetallic catalysts have been identified for the CO₂ + C₃H₈ system; one is selective toward reforming (C-C bond cleavage) and the other favors dehydrogenation (C-H bond scission).

 References

(1) Plotkin, J. S. ACS News Industrial Chemistry & Engineering. 2016, pp 1–4.

(2) Wang, S.; Zhu, Z. H. Energy and Fuels 2004, 18 (4), 1126–1139.