Rare Earth Metals Offer a New Way to Steer Glycerol Into Valuable Chemicals

Glycerol, the humble byproduct that pours out of the world’s biodiesel reactors by the megaton, has long been both a blessing and a headache for the chemical industry. It already finds use in pharmaceuticals, personal care products, food, polymers, and specialty chemicals, but chemists have wanted something more ambitious: a way to electrochemically upgrade this cheap three-carbon alcohol into higher-value molecules while simultaneously making hydrogen fuel. A new review published in Advances in Industrial and Engineering Chemistry argues that an unlikely family of elements, the rare earth metals, may hold the key to controlling one of electrocatalysis’s most tangled reaction networks.

Electrochemical glycerol oxidation, or GOR, is attractive for two reasons. First, it converts a biomass-derived feedstock into chemicals such as glyceric acid, glycolic acid, formic acid, and lactic acid. Second, it can replace the oxygen evolution reaction, the sluggish half-reaction that normally dominates the energy budget of water electrolysis, thereby lowering the voltage needed to produce hydrogen at the cathode. The catch is selectivity. Glycerol carries three hydroxyl groups, and once it lands on a catalyst surface it can follow a bewildering set of parallel routes involving adsorption, dehydrogenation, carbon-hydrogen activation, and carbon-carbon bond scission, ultimately branching into competing C3, C2, and C1 products. Higher catalytic activity, the review emphasizes, does not automatically translate into higher selectivity, and a persistent trade-off between the two has frustrated catalyst designers for decades.

The review, authored by Jayasmita Jana and Seung Hyun Hur, takes stock of what rare earth metals, which include the lanthanides along with scandium and yttrium, actually do when they are built into glycerol-oxidation electrodes. These elements bring distinctive physicochemical assets: localized 4f orbitals in the lanthanides, weak covalent bonding character, tunable oxidation states, Lewis acidity, and a strong affinity for oxygen. Lanthanide oxides such as ceria, gadolinia, lanthana, and samaria add oxygen vacancies, redox flexibility, and surface basicity to the toolbox. The central question the authors pose is whether these metals act as true active sites or as promoters, reshaping the reaction landscape through electronic redistribution, metal-oxygen interactions, lattice distortion, and surface reconstruction.

Cerium emerges as the most extensively studied player. In ceria-supported platinum systems, the generation of active hydroxyl species on CeO2 accelerates glycerol oxidation kinetics, while ceria modifies the electronic structure of platinum, reduces the adsorption of glyceric acid, and alleviates catalyst poisoning. Ceria has also been credited with an anti-poisoning effect toward carbon monoxide. In one striking example, a Pt52(CeO2)48/C anode directed the reaction toward more oxidized products, a shift tracked by in situ infrared bands assigned to glycerate, glycolate, oxalate, and formate. In another, adding CeO2 to gold catalysts on carbon nanotubes raised glycerol conversion and promoted glyceric acid formation, because the oxide particles reduced glyceric acid adsorption on the gold surface, curbed poisoning, and kept more active sites available. The same oxide even suppressed gold agglomeration and maintained glyceric acid formation over five reaction cycles.

Other rare earth elements steer the reaction in different directions. A cobalt oxide-ceria heterojunction with a built-in electric field shifted the cobalt oxide d-band center upward and delivered 42 percent selectivity toward glycolic acid, a C2 product, by inhibiting further carbon-carbon cleavage. A ceria-based catalyst dispersed in cobalt oxide and coated with amorphous carbon instead favored complete carbon-chain breakdown, pushing selectivity toward formate, a C1 product, with the Ce3+/Ce4+ ratio controlling oxygen storage and surface oxygen availability. Europium compounds have proven equally potent: a Eu2O3 composite with graphitic carbon nitride achieved 78 percent selectivity toward formate at 1.4 volts over 12 hours, while a Eu3O4/tungsten oxide material demonstrated efficient coupled glycerol oxidation and hydrogen evolution at a fairly low cell voltage. Terbium doping of tin selenide quantum dots introduced Tb3+/Tb4+ redox sites and lattice strain that lowered the barrier for selective carbon-carbon bond cleavage, converting a catalyst that normally made C3 glyceric acid into one producing glycolic and formic acids.

Perhaps the most mechanistically revealing case involves yttrium alloyed into platinum-lead mesoporous nanosheets. Using in situ Raman and infrared spectroscopy, researchers tracked the disappearance of glycerol’s carbon-oxygen-hydrogen vibrational bands and the rise of glyceraldehyde signatures, confirming that glyceraldehyde forms as an intermediate on the road to glyceric acid. Compared with the undoped PtPb catalyst, the yttrium-containing version showed stronger glyceraldehyde-related bands and negligible formic acid formation. Density functional theory calculations attributed this to stronger glycerol adsorption, easier hydroxyl attack, lower overall reaction free energies, and preferential glyceraldehyde desorption. The alloying lowered the glyceric acid desorption barrier from 1.34 to 0.92 electron volts, suppressing carbon-carbon cleavage and delivering a glyceric acid selectivity of 72.5 percent. The authors classify this as pathway regulation rather than mere promotion: the rare earth element changed the relative energetics of competing elementary steps, not just the overall reaction rate.

Context matters enormously in this chemistry. Higher glycerol concentrations tend to preserve C3 products by saturating active sites, while higher pH drives more extensive oxidation and carbon-carbon cleavage toward C2 and C1 products. Acidic media slow the reaction and favor carbon-bound adsorption, whereas alkaline conditions favor oxygen-bound adsorption and different product slates. Isotope-labeling work on a cobalt-nickel oxide using carbon-13 labeled glycerol confirmed a stepwise route from glycerol through glyceraldehyde and glycerate to glycolate and formate, with extensive, regioselective cleavage of the bond adjacent to carboxyl groups and only about 2 percent of product further oxidized to carbonate. The review also stresses rigorous analytics: product identification demands validated chromatographic methods, isotope labeling, and full carbon balances including carbonate and gaseous carbon dioxide, since sloppy quantification can inflate apparent selectivity.

The industrial outlook is cautiously encouraging but far from settled. An Au-CeO2/CNT electrode achieved 99.7 percent glycerol conversion and 50.0 percent glyceric acid selectivity after 12 hours at 1.12 volts versus reversible hydrogen electrode in 1.0 M potassium hydroxide. Flow electrolyzers have reached 85 percent lactic acid selectivity at current densities above 400 milliamperes per square centimeter with a productivity of 68.9 millimoles per hour, setting a benchmark that rare earth systems have yet to match under prolonged operation. Techno-economic analyses have estimated a minimum selling price of $2.30 per kilogram for electrochemically produced glyceric acid, compared with $4.91 per kilogram for conventional oxidation, and a solketal process reported a break-even price of 4.90 euros per kilogram. Still, the review is explicit that no thorough techno-economic evaluation specific to lanthanide-mediated glycerol oxidation exists, and the current literature does not justify claiming economic superiority over transition-metal electrodes.

Durability looms as the decisive obstacle. Under prolonged anodic conditions, lanthanide-containing electrodes risk metal leaching, potential-induced surface reconstruction, particle agglomeration, catalyst-layer detachment, poisoning, and overoxidation, and glycerol depletion can trigger the oxygen evolution reaction and shift selectivity. The authors argue that short-cycle laboratory tests are insufficient and call for flow or zero-gap electrolysis cells operating at 300 to 500 milliamperes per square centimeter or more, with extended runs and post-mortem analysis by diffraction, photoelectron and X-ray absorption spectroscopy, electron microscopy, and quantitative mass spectrometry to distinguish true structural stability from gradual dissolution of the rare earth component.

The bigger picture is that rare earth metals are not a universal fix but a versatile set of levers. Depending on chemical state and incorporation mode, they can serve as promoters of oxide species, alloying elements, regulators of interfacial charge, or partners in heterojunctions, influencing glycerol adsorption, hydroxyl activation, intermediate binding, and the competition between chain cleavage and selective C3 oxidation. Because lanthanides cost more than transition metals, the review favors low-loading doping of earth-abundant electrodes over lanthanide-rich catalysts. The field’s next frontier, the authors conclude, lies in proving that rare earth engineering can deliver comparable current densities and yields while improving intermediate control, electrode durability, and selectivity, without excessive material costs or leaching risks, ideally in flow-cell and zero-gap electrolyzers running on realistic glycerol feeds for extended periods.

Subject of Research: Rare earth metal-mediated electrocatalysts for selective glycerol electrooxidation and coupled hydrogen production

Article Title: Rare earth metal-mediated electrode for glycerol electrooxidation: interfacial chemistry and reaction selectivity

Article References: Jana, J., & Hur, S. H. (2026). Rare earth metal-mediated electrode for glycerol electrooxidation: interfacial chemistry and reaction selectivity. Advances in Industrial and Engineering Chemistry, 2(1), Article 15. https://doi.org/10.1007/s44405-026-00055-y

Image Credits: AI Generated

DOI: 10.1007/s44405-026-00055-y

Keywords: glycerol electrooxidation, rare earth metals, electrocatalysis, cerium oxide, product selectivity, hydrogen production, biomass valorization, carbon-carbon bond cleavage, oxygen vacancies, in situ spectroscopy, doping, flow electrolysis