(192f) Identification of the Active Catalyst Phases of the Bimetallic Cobalt and Palladium Zinc Oxides for the Reforming Reactions of Alcohols

Pd/ZnO and Co/ZnO have been shown to be effective alcohol reforming catalysts[1-3]and thus can be used to make hydrogen from renewable feedstocks. Recent studies have shown that an active component of the Pd/ZnO system under CH3OH reforming conditions is a PdZn alloy[4] which is formed under reaction conditions[5]. The precise roles of PdZn alloy and the ZnO [6]support in the decomposition, Eqn 1, and reverse water-gas-shift (RWGS), Eqn 2,reactions is unknown.

(1)CH3OH=CO2+2H2

(2)CO+H2O=CO2+H2

Also unknown is the role of these zinc alloys (especially CoZn) in the reforming of CH3CH2OH, which includes a more complex decomposition step which also requires C-C bond breaking, Eqn 3,(3) CH3CH2OH+H2O=2CO+4H2

While it is known that oxide support have a role in the reforming reaction it is difficult to determine the role of the oxide support since bimetallic catalysts are typically made by impregnating a metal onto an oxide. Here we show that a thermodynamically stable, unsupported alloy phase can be readily prepared via aerosol synthesis with adequate surface area for catalytic activity measurements. The synthesis method allows great flexibility in synthesizing a range of alloy compositions, and it is also possible to vary particle sizes by changing the aerosol generator and precursor concentrations.

In effort to better understand the role of Pd and Co zinc-alloys in the reforming reactions of both CH3OH and CH3CH2OH we have prepared single phase, unsupported, bimetallic zinc alloys of different compositions so as to investigate the effect of alloy composition on catalytic activity. Partial oxidation of the metal alloy also allows us to generate a ZnO phase in-situ, allowing us to identify the most active and stable phases for alcohol reforming catalysts. In parallel with elucidation of reaction sites this investigation seeks to identify reaction intermediates and thus detailed reaction pathways and energetic requirement for alcohol steam reforming on zinc alloys.

References

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5. Conant, T.; Karim, A. M.; Lebarbier, V.; Wang, Y.; Girgsdies, F.; Schlogl, R.; Datye, A., Journal of Catalysis 2008, 257 (1), 64-70.

6. Karim, A. M.; Conant, T.; Datye, A. K., Phys. Chem. Chem. Phys. 2008, 10 (36), 5584-5590.