(687e) The Preferential Electrochemical Activity of Au and Pd Nanoparticles on Conductive Carbon Support Boosts Oxidative Dehydrogenation of Hydroxymethylfurfural.

Selective oxidation of biomass-derived chemicals is a route to key intermediates for a range of products. Given the high relative oxygen content of many biomass-based chemicals, discovering effective catalysts for the selective oxidative dehydrogenation (ODH) of alcohols and aldehydes is an active research area.

Applying the important platform chemical hydroxymethylfurfural (HMF) as a model reactant, containing both alcohols and aldehydes, we discovered the ODH rate was dramatically enhanced (2.4 times) upon placing spatially separated Au and Pd nanoparticles (i.e., physical mixture, Au@Pd/C) onto electronically connected supports, compared to rates from sum of monometallic catalysts (Au/C and Pd/C). Our understanding of this enhancement lies in considering the overall ODH reaction as two coupled half-reactions; dehydrogenation (DH) and the oxygen reduction reaction (ORR). We propose that this rate enhancement is due to electrochemically coupling between Au/C selectively performing DH and Pd/C selectively performing ORR. This proposed mechanism, which we term cooperative redox coupling enhancement (CORE), is studied utilizing standard electrochemical approaches.

Electrochemical HMF oxidation reaction (HMFOR) and ORR tests revealed that Au/C has an excellent HMFOR and poor ORR activity. In contrast, Pd/C showed an excellent ORR and poor HMFOR activity. Therefore, the overall thermocatlytic HMFOR activity of the Au@Pd/C can be significantly enhanced by electrochemical redox coupling of Au/C (HMFOR) and Pd/C (ORR), as observed in the thermocatalytic test. The electrochemical coupling was confirmed by monitoring the short-circuit current flow from Au/C to Pd/C in a dual-chamber electrochemical cell. The CORE effect supports an evident relationship between the aqueous-phase ODH of alcohols and aldehydes and the corresponding electrochemical half reactions. Furthermore, the CORE effect implies the electrochemical understanding of thermocatalytic reactions can enable the designing of effective thermocatalysts.