Rising atmospheric concentration of CO2 is forecasted to have potentially disastrous effects on the global climate due to its role in global warming and ocean acidification [1].  A catalytic process that utilizes CO2 as a feedstock to make carbon monoxide, methanol, and methane is potentially more desirable than sequestration.  CO is a desired product because it can be integrated into down-stream processes to produce synthetic fuels via Fischer-Tropsch.The reduction of CO2 by hydrogen has been conducted on supported catalysts in a batch reactor at 573 K.  Catalysts synthesized on a reducible support (CeO2) showed higher activity than on an irreducible support (?-Al2O3) [3].  The active metal also played an important role in controlling the selective reduction of CO2 to CO instead of CH4.  Extended X-ray absorption fine structure (EXAFS) and transmission electron microscopy (TEM) confirmed the formation of uniform, bimetallic particles.  Among the monometallic and bimetallic catalysts evaluated in a batch reactor, PdNi/CeO2 was found to be the most active bimetallic catalyst, but formed the greatest amount of CH4.  PtCo/CeO2 showed the highest selectivity to CO with very low selectivity to CH4.  The selectivity of each catalyst correlated with the d-band center value of each bimetallic surface.  Among the catalysts investigated, bimetallic catalysts with values of d-band center farther from the Fermi level produced more CO and less CH4 than catalysts with values closer to the Fermi level.  The trends in selectivity were confirmed in a flow reactor under similar reaction conditions.The reactivity of CO2 over molybdenum carbide (Mo2C) is somewhat analogous to the oxidation storage capacity seen in ceria; however, in this case, Mo2C cycles between carbide and oxy-carbide.  Therefore, it is advantageous to modify Mo2C with a metal that can dissociate the product, CH4, and thereby recarburize the catalyst to maintain the active phase.  In-situ XANES experiments were used to study the oxidation state of Mo in Mo2C.  These experiments suggested that an oxidation-carburization cycle contributed to the high activity of Mo2C based catalysts and that Mo2C was maintained in a carburized state during CO2 reduction by hydrogen. References[1]T.R. Knutson, R.E. Tuleya, J. Clim. 17 (2004) 3477-3495.[2]D.C. LaMont, W.J. Thomson, Chemical Engineering Science 60 (2005) 3553-3559.[3] 257.  M.D. Porosoff and J.G. Chen, Journal of Catalysis, 301 (2013) 30-37.

Trends in CO<sub>2</sub> hydrogenation activity and selectivity over bimetallic and carbide catalysts

248th National Meeting (2014)

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Trends in CO2 hydrogenation activity and selectivity over bimetallic and carbide catalysts

Trends in CO₂ hydrogenation activity and selectivity over bimetallic and carbide catalysts