posted on 2024-01-16, 16:09authored byJay Pee Oña, Laura Laverdure, Rose Marie Latonen, Narendra Kumar, Markus Peurla, Ilari Angervo, Karoliina Honkala, Henrik Grénman
The
electrocatalytic oxidation (ECO) of glucose on gold requires
alkaline conditions and relatively high potentials (>0.3 VRHE). Although the adsorption of hydroxide ions (OHads) is
also known to occur under these conditions, the generally accepted
proton-coupled electron transfer mechanism for sugar ECO does not
explicitly state the role of OHads in the sugar adsorption
or oxidation steps. To investigate this, we carried out a combined
experimental and density functional theory (DFT) study on the ECO
of glucose and xylose over a nanogold catalyst under temperature and
pH control. Grand canonical DFT (GC-DFT) was used to identify the
preferred reaction mechanism in which OHads facilitates
the thermodynamically feasible formation of gluconic and xylonic acid.
Calculated results also showed that OHads plays a role
in improving the acid selectivity. Constant-potential electrolyses
in sugar solutions were performed using mesoporous (Sibunit) carbon-supported
Au nanoparticles (AuNPs) with an average cluster size of 4.7 nm. Experimental
results showed that the highest conversions for glucose (57.7%) and
xylose (49.4%) were obtained at 25 °C and pH 12.5, with gluconic
and xylonic acid selectivity of 81.5 and 87.8%, respectively. The
catalytic activities were high considering the low Au loading (∼0.1%
wt). Higher pH led to a decrease in the ECO rate possibly due to excess
hydroxide ions blocking active sites for sugar adsorption. Our results
highlight the importance of computational studies in elucidating reaction
mechanisms for sugar ECO where sugar acids are the main oxidation
products. This is crucial in designing reaction systems for the viable
production of these value-added chemicals from biomass.