Partial Electrooxidation of Glycerol on Close-Packed Transition Metal Surfaces: Insights from First-Principles Calculations

Glycerol is a byproduct
of biodiesel production and an abundant
feedstock for the synthesis of high-value chemicals. One promising
approach for valorization of glycerol is electrooxidation yielding
hydrogen and value-added products. However, due to the vast amount
of intermediary steps and possible products, the process is not fully
understood. Here, the first two deprotonations of glycerol on close-packed
transition metals (Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, and Au) are
investigated using density functional theory calculations together
with the computational hydrogen electrode. We find that the theoretical
limiting potential for the studied reaction is close to 0 V vs the
reversible hydrogen electrode, ranging from −0.12 V for ruthenium
to +0.35 V for gold. Furthermore, the results show that Ru, Rh, Ir,
Ag, and Au are selective toward dihydroxyacetone and its derivatives,
while Pd and Pt are selective toward either dihydroxyacetone or glyceraldehyde
and their derivatives, and that Cu, Co, and Ni are selective toward
hydropyruvic acid. The results can be rationalized in terms of the
relative bond strengths of carbon and oxygen on the metal. In addition,
we find that solvent effects are generally small, the exceptions being
the limiting potential on copper and the mechanism on rhodium. These
results can be used to steer the selectivity toward more valuable
products and thereby increase the economic yield of biodiesel production.