C–C Bond Formation Coupled with C–C Bond Cleavage during Oxidative Upgrading of Glycerol on a Nanoporous BiVO₄ Photoanode

Abstract

Production of biodiesel generates glycerol as a 10 wt% byproduct. Therefore, efficient and selective glycerol upgrading is critical for the sustainable production of biodiesel as well as for the production of chemicals from renewable feedstocks. In this study, the photo­electro­chemical glycerol oxidation reaction (GOR) was investigated using a nanoporous BiVO4 photo­anode in pH 9.3 and pH 2 buffer solutions. In both solutions, glycol­aldehyde (GCAD), a C2 species, was the major product, which has never been the major product in any previous electro­chemical or photo­electro­chemical GOR study. To produce GCAD from the C3 species glycerol, C–C cleavage should occur to produce C2 and C1 species with a 1:1 ratio. Intriguingly, our results show that, during photo­electro­chemical GOR on BiVO4, more GCAD is produced than can be explained by simple C–C cleavage, meaning that GCAD is also produced from C–C coupling of two C1 species produced from C–C cleavage. This is equivalent to converting two glycerol molecules to three GCAD molecules, which offers an extra­ordinary way to maximize GCAD production. To gain further insight into the nature of this unprecedented C–C coupling during GOR, photo­electro­chemical oxidation of intermediate oxidation products (glycer­aldehyde and 1,3-dihydroxy­acetone) and glycerol-1,3-13C2 was compared to that of standard glycerol. Photo­electro­chemical GOR was also compared with electro­chemical GOR on BiVO4 to interrogate whether light is critical for the observed C–C coupling. Results obtained from comprehensive control experiments revealed critical information about C–C cleavage and C–C coupling during GOR on BiVO4.

Electrolyte selection toward efficient photoelectrochemical glycerol oxidation on BiVO4

“…In NaNO 3 , the selectivity for GCAD exceeded 50% and the selectivity for GLAD was as low as 14%. These results suggest that the rate of C–C cleavage in GLAD, which was proposed as a pathway to the formation of GCAD and FA, 16 might differ among various electrolyte solutions, consequently influencing the overall GOR performance. One possible explanation is that GLAD adsorbs more favorably onto the BiVO 4 surface in the NaNO 3 solution compared to others.…”

“…Notably, GCAD emerged as the most dominant product in all electrolytes, which is consistent with a recent report. 16 However, the selectivity varied depending on the electrolyte. In K 2 SO 4 , the selectivity for GLAD (28%) a C3 molecule, was the highest among the electrolytes tested.…”

Solar-driven highly selective conversion of glycerol to dihydroxyacetone using surface atom engineered BiVO4 photoanodes

“…8 ), nearly twice that of a C-C single bond (1.54 Å). The spacing makes it difficult for neighboring carbon atoms to be adsorbed simultaneously, which may be a cause of the suppression of C-C bond breaking 43 . The above two reasons would act as main factor for continuous DHA production.…”

Selective Oxidation of Alcohol to Valuable Aldehydes Using Water as a Promoter in a Photoelectrochemical Cell

“…The pioneering work conducted by the Choi laboratory elegantly showcased the concept of PEC alcohol oxidation through a 2,2,6,6-tetramethylpiperidinooxy (TEMPO) mediated reaction, converting 5-hydroxymethylfurfural (HMF) into 2,5-furandicarboxylic acid (FDCA) . More recently, PEC organic oxidation has gradually expanded to encompass a variety of aliphatic alcohols (such as methanol, , glycerol, , sugar, ethylene glycol) and aromatic alcohols (including benzyl alcohol − and furfuryl alcohol). Despite the development of a wide range of reactions, the application of PEC in the oxidation of alcohols to aldehydes is still in its infancy, often resulting in overoxidation to acids, poor selectivity, or a decrease in selectivity over time.…”