452810 Development of Catalysts for CO2 Hydrogenation to Olefins

Wednesday, November 16, 2016: 10:18 AM
Franciscan C (Hilton San Francisco Union Square)
Marc D. Porosoff, NRC Postdoctoral Fellow and Heather D. Willauer, Materials Science

The Naval Research Laboratory (NRL) is investigating a catalytic process to produce synthetic jet fuel from CO2 and H2.  The current method consists of extracting CO2 from seawater, then combining the extracted CO2 with H2 produced through water electrolysis.  The CO2 and H2 are then reacted over catalysts in two steps to first produce olefins (C2-C4), which are oligomerized into the liquid hydrocarbon fraction (C6-C17) for synthetic jet fuel.  Although there are several promising catalysts for both reaction steps, problems exist with water removal, which prevents high conversion of CO2 and high selectivity towards liquid hydrocarbons.  Future directions require carefully controlled synthesis of new catalysts that are water tolerant and improve the activity and selectivity of CO2 hydrogenation to olefins for liquid hydrocarbon synthesis.

One of the most difficult aspects of chemistry involving CO2 is not the catalytic activation, but the thermodynamic limitation of utilizing the highly stable molecule.[1]  By coupling the endothermic reverse water-gas shift (RWGS) reaction with the slightly exothermic Fischer-Tropsch (FT) process, FT from CO2 and H2 (CO2-FT) becomes more favorable as higher chain compounds are formed.[1-2]  However, high conversion of CO2 can only be achieved if the FT step is fast enough to overcome the thermodynamic limitation of RWGS, which is the main challenge for reactions involving CO2.  Therefore, to effectively synthesize jet fuel from CO2 and H2, new catalysts must be identified which are active for both RWGS and FT. 

Because the cost of catalysts for CO2 hydrogenation is also important, catalysts must be synthesized from low-cost materials.  Mo2C/γ-Al2O3 is a promising catalyst because of the ease of synthesis, low-cost, high activity, and relatively low oxygen binding energy (OBE), which allows it to freely exchange oxygen with CO2.  A previous study showed that Mo2C was active and selective for CO2 reduction into CO.[3]  Mo2C also has a much lower OBE than other transition metal carbides (TMCs), which contributes to its high CO2 hydrogenation activity.  By doping Mo2C with Fe, it is possible to further enhance the activity for FT, as Fe-based catalysts are highly active for olefin production through FT and CO2-FT.[4]

References

[1] K. Müller, L. Mokrushina, W. Arlt, Chemie Ingenieur Technik 2014, 86, 497-503.

[2] U. Rodemerck, M. Holeňa, E. Wagner, Q. Smejkal, A. Barkschat, M. Baerns, ChemCatChem 2013, 5, 1948-1955.

[3] M. D. Porosoff, X. Yang, J. A. Boscoboinik, J. G. Chen, Angewandte Chemie International Edition 2014, 53, 6705-6709.

[4] H. D. Willauer, R. Ananth, M. T. Olsen, D. M. Drab, D. R. Hardy, F. W. Williams, Journal of CO2 Utilization 2013, 3–4, 56-64.


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See more of this Session: Catalysis for C1 Chemistry I: CO2 Conversion
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