Direct and Indirect Electrooxidation of Glycerol to Value‐Added Products

Abstract

In this work, different approaches for the direct and indirect electrooxidation of glycerol, a by‐product of oleochemistry and biodiesel production, for the synthesis of value‐added products and of intermediates for biofuel/electrofuel production, were investigated and compared. For the direct electrooxidation, metallic catalysts were used, whose surfaces were modified by promoters or second catalysts. Bi‐modified Pt electrodes (PtxBiy/C) served as model systems for promoter‐supported electrocatalysis, whereas IrO2‐modified RuO2 electrodes were studied as catalyst combinations, which were compared under acidic conditions with the respective monometallic catalysts (Pt/C, RuO2/Ti, IrO2/Ti). Furthermore, inorganic halide mediators (chloride, bromide, iodide) and organic nitroxyl mediators (4‐oxo‐2,2,6,6‐tetramethyl‐piperidin‐1‐oxyl and 4‐acetamido‐2,2,6,6‐tetramethyl‐piperidin‐1‐oxyl) were evaluated for indirect electrooxidation. These different approaches were discussed regarding selectivity, conversion, and coulombic efficiency of the electrochemical glycerol oxidation.

Earth‐Abundant Metal‐Based Electrocatalysts Promoted Anodic Reaction in Hybrid Water Electrolysis for Efficient Hydrogen Production: Recent Progress and Perspectives

“…Over last decades, the glycerol oxidation reaction (GOR) has been carried out as a promising approach to reform glycerol into useful commodity chemicals in order to balance the utilization and the large supply of glycerol, [114] but majorly driven by noble metal-based electrocatalysts. [115][116][117][118] As glycerol is a C3 alcohol, its oxidation products range from C1 to C3, such as dihydroxyacetone, glyceraldehyde, glyceric acid, glycolic acid, lactic acid, hydroxypyruvic acid, formic acid, and so on. [110,111] Thus, glycerol-assisted HWE can have different cell voltages and H 2 production rate, which is directly determined by the reaction pathways.…”

Electrolysis of glycerol to value‐added chemicals in alkaline media

“…Selective oxidation of glycerol is still a challenge owing to its three reactive hydroxyl groups, which results in the production of a variety of products subject to the catalyst and reaction conditions. The selectivity depends on the experimental conditions (anode catalyst, electrolyte, pH, applied potential and temperature) 8 . Some of these products could include glyceraldehyde, dihydroxyacetone, tartronic acid and glyceric acid, which are C 3 products that have high economic value and industrial interest.…”

“…The selectivity depends on the experimental conditions (anode catalyst, electrolyte, pH, applied potential and temperature). 8 Some of these products could include glyceraldehyde, dihydroxyacetone, tartronic acid and glyceric acid, which are C 3 products that have high economic value and industrial interest. For instance, glyceraldehyde and dihydroxyacetone are applied in the cosmetics industry to produce skin treatment and tanning lotions.…”

Electrochemical Oxidation of Glycerol to Dihydroxyacetone in Borate Buffer: Enhancing Activity and Selectivity by Borate–Polyol Coordination Chemistry

“…The global glycerol production was 3.6 billion liters in 2016 and is projected to reach 4.0 billion liters per year by 2026 . The abundance of glycerol has motivated the research for upgrading glycerol to value-added products, thus making biodiesel production more environmentally benign and economically feasible. − In 2004, the US Department of Energy had listed glycerol as one of the top 12 sugar-derived platform building blocks …”

“…The electrocatalytic glycerol oxidation reaction (EGOR) driven by renewable electricity (such as solar and wind) is a promising pathway for fine chemical production. ,− Currently, most of the developed electrocatalysts for the EGOR are based on precious noble metals, such as Pt, Au, Pd, and its alloys. − Advantages of using these noble metal electrocatalysts include low oxidation overpotential and ability to obtain a plethora of valuable C 3 products such as glyceraldehyde (GLAD), glyceric acid (GLA), and dihydroxyacetone (DHA). However, when earth-abundant, low-cost transition metal electrocatalysts are used, the deep oxidation product such as formic acid (FA) is most often obtained. − Therefore, significant challenges remain in searching for a suitable glycerol electro-oxidation system that is cost-effective, sustainable, resistant to carbonaceous species poisoning, and capable of replacing the expensive noble metals in producing value-added C 3 products. , …”