Abstract
Acetol – a dehydration product of glycerol – can be selectively reduced to 1,2-propanediol and acetone through hydrogenation and dehydroxylation reactions, thereby providing a platform toward an efficient upgrading of biomolecules. To shed light on the relationship between the reactivity and the electrode structure, we report the electrochemical reduction of acetol on low-index platinum single crystals and their corresponding epitaxial palladium monolayers (PdML). Combining cyclic voltammetry and in-situ spectroscopy measurements, Pt(110) and Pt(111) are shown to be active surfaces for acetol adsorption and reduction at potentials near 0 V vs.RHE, though accompanied by the dissociative adsorption of acetol to poisoning CO. For the Pt(100) surface, the activities of both acetol reduction and hydrogen evolution are inhibited by the most prominent CO poisoning among the three surfaces. In contrast, no electrochemical acetol reduction is detected on palladium monolayer near 0 V vs.RHE, irrespective of the surface crystallographic orientation. However, acetol decarbonylation still proceeds especially on PdMLPt(110), which suffers from the most severe poisoning from the low-index surfaces. Furthermore, to access practical applications, we extend the study on the effect of the electrode material, the applied potential, and the electrolyte pH on the selectivity of acetol reduction. At sufficiently negative potentials, Au and Pt are appropriate candidates toward hydrogenation reaction to 1,2-propanediol at Ph = 3, whereas Pd exhibits the ability to produce both 1,2-propanediol and acetone at pH = 1 and pH = 3, the selectivity of which is strongly dependent on the potential. Given these mechanistic insights into acetol adsorption and reduction at the specific electrodes and facets, this work provides guidance on how to rationally design electrocatalysts toward efficient electrochemical hydrogenation.
Highlights
Electrochemical conversion of biomass feedstock to value-added chemicals and fuels would be a significant step toward a carbonneutral cycle, allowing for an upgrading platform using renewable electricity [1,2,3]
In view of the complexity and toxicity of nitrogen oxide (NO), we adopted underpotential deposition: Pd was deposited started from 0.95 V vs.reversible hydrogen electrode (RHE) to negative potentials in a solution containing 0.1 M H2SO4, 10−4 M PdCl2, and 9 × 10−3 M HCl at very low scan rate of 0.1 mV s−1, until a charge of 418 μC cm−2 was obtained, which corresponds to one Pd atomic layer [33]
An electrochemical annealing process was conducted by cycling voltammetry of the prepared electrode between 0.4 V and 0.06 V vs.RHE at 10 mV s−1 in 0.1 M H2SO4 solution. We refer to these monolayer surfaces as PdMLPt(111), PdMLPt(110), and PdMLPt(100)
Summary
Electrochemical conversion of biomass feedstock to value-added chemicals and fuels would be a significant step toward a carbonneutral cycle, allowing for an upgrading platform using renewable electricity [1,2,3]. Studies on electrochemical hydrogenation of carbonyl compounds, such as 5-hydroxymethylfurfural [6], glucose [7], ethyl pyruvate [8], have attracted great attention Since they involve multiple functional groups, the active and selective conversion of these molecules are correlated closely with the electrode surface and the chemical environment [9]. Knowing the activity on different facets, we extend the study to other electrodes, different electrolyte pH, and more negative potentials, to show the selective reduction of acetol to 1,2-PD and acetone, respectively. In this way, we can identify the catalysts and reaction conditions needed in the cascade upgrading of glycerol to 1,3- and 1,2-PD
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