Insight into selectivity differences of glycerol electro-oxidation on Pt(111) and Ag(111)

Electro-oxidation is a way to utilize glycerol, a byproduct of biodiesel production, to produce fuels and feedstock chemicals for the chemical industry. A significant challenge is to get products with high selectivity, so it is desirable to understand the glycerol oxidation mechanisms in further details. Using density functional theory calculations, we investigate possible glycerol oxidation intermediates on Pt(111) and Ag(111). We find that the different adsorption preferences of the intermediates on Pt (adsorption via carbon atoms) and on Ag (adsorption via oxygen atoms) lead to different preferred reaction pathways, resulting in different products. The reaction pathways on both surfaces involve glyceraldehyde as a key intermediate, however, upon further oxidation, Pt(111) preferentially produces glyceric acid (CH2OH-CHOH-COOH), while on Ag(111) C-C bonds are broken and leads to production of glycolaldehyde and formic acid (CH2OH-CHO and HCOOH). These predictions agrees well with the experimental outcome of electro-oxidation of glycerol on Pt and Ag surfaces. Our study therefore provides useful insights for optimizing the selectivity of glycerol oxidation and improving the utilization of glycerol.