Partial Electrooxidation of Glycerol on Close-Packed Transition Metal Surfaces: Insights from First-Principles Calculations
Mikael Valter, Egon Campos dos Santos, Lars G. M. Pettersson, Anders Hellman
Abstract
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.