Understanding and Suppressing C-C Cleavage during Glycerol Oxidation for C3 Chemical Production

Biodiesel production generates considerable quantity of glycerol as a byproduct, and electrochemical oxidative upgrading of glycerol to various value-added chemicals is an area of great interest. While glycerol has the potential to be converted into a variety of useful C3 products, C-C cleavage reactions often dominate during electrochemical glycerol oxidation, resulting in formic acid, which is a C1 product, as the major product. Due to a current lack of understanding of the key factors that affect the C-C cleavage reactions, the development of rational strategies to suppress the C-C cleavage reactions has been limited thus far. In this study, we investigated glycerol oxidation on two non-noble metal catalysts, MnOx (x = similar to 2) and MnSb2O6. Both of these catalysts are stable in a wide pH range (1-14), making it possible to systematically study the effects of pH on C-C cleavage during glycerol oxidation. Furthermore, while MnOx and MnSb2O6 both have Mn as the active catalytic center, the oxidation state (mostly Mn4+ for MnOx and Mn2+ for MnSb2O6) and structural features (nearby Mn sites for MnOx and isolated Mn sites for MnSb2O6) of Mn in these two catalysts are different. By comparing glycerol oxidation on these two catalysts under various pH and potential conditions, the current study provides an insightful understanding of the species that undergo C-C cleavage and the key factors that affect C-C cleavage during glycerol oxidation. This results in the identification of conditions to produce glyceric acid, a C3 product, as the major product, with a relative selectivity as high as 82%.