Experimental and Theoretical Investigation of the Role of Bismuth in Promoting the Selective Oxidation of Glycerol over Supported Pt–Bi Catalyst under Mild Conditions

Mechanistic Insights into Glycerol Oxidation to High-Value Chemicals via Metal-Based Catalysts

The oxidation of glycerol offers a valuable route for producing high-value chemicals. This review provides an in-depth analysis of the current advancements and mechanistic insights into novel metal-based catalysts for glycerol oxidation. We discuss the catalytic roles of both precious metals (e.g., Pt, Pd, Au), noted for their high efficiency and selectivity, and cost-effective alternatives, such as Ni, Cu, and Fe. Bimetallic and metal oxide catalysts are highlighted, emphasizing synergistic effects that enhance catalytic performance. This review elucidates the key mechanism involving selective adsorption and oxidation, providing detailed insights from advanced spectroscopic and computational studies into the activation of glycerol and stabilization of key intermediates, including glyceraldehyde and dihydroxyacetone. Additionally, selective carbon-carbon bond cleavage to yield smaller, valuable molecules is addressed. Finally, we outline future research directions, emphasizing the development of innovative catalysts, deeper mechanistic understanding, and sustainable process scale-up, ultimately advancing efficient, selective, and environmentally friendly catalytic systems for glycerol valorization.

Copper-Doped NiOOH for the Electrocatalytic Conversion of Glycerol to Formate via the Inhibition of the Oxygen Evolution Reaction

The combination of the electrocatalytic glycerol oxidation reaction (GOR) with the cathodic hydrogen evolution reaction serves to reduce the anodic overpotential, thereby facilitating the efficient production of hydrogen. However, the GOR is confined to a narrow potential range due to the competition of the oxygen evolution reaction (OER) at high potential. Therefore, it is necessary to develop a catalyst with a high Faraday efficiency of formate (FEFA) over a wide potential range. Herein, Cu-doped NiOOH catalysts were synthesized by electrodeposition to inhibit the competing OER during the GOR process, achieving a current density of 10 mA cm-2 at 1.278 V vs RHE, a FEFA over 70.36% within a broad potential range of 1.3 V vs RHE to 1.6 V vs RHE, and a maximum FEFA of 96.46% at 1.35 V vs RHE. In situ spectral studies and DFT calculations revealed that Cu doping slowed the *OH to *O step for the inhibition of the OER and enhanced glycerol adsorption to accelerate the GOR. A competitive reaction mechanism for boosting glycerol electro-oxidation to formate was proposed, presenting a feasible strategy for the highly selective production of electrocatalytic value-added chemicals and the sustainable production of hydrogen energy.

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

Dihydroxyacetone is the most desired product in glycerol oxidation reaction because of its highest added value and large market demand among all possible oxidation products. However, selectively oxidative secondary hydroxyl groups of glycerol for highly efficient dihydroxyacetone production still poses a challenge. In this study, we engineer the surface of BiVO4 by introducing bismuth-rich domains and oxygen vacancies (Bi-rich BiVO4-x) to systematically modulate the surface adsorption of secondary hydroxyl groups and enhance photo-induced charge separation for photoelectrochemical glycerol oxidation into dihydroxyacetone conversion. As a result, the Bi-rich BiVO4-x increases the glycerol oxidation photocurrent density of BiVO4 from 1.42 to 4.26 mA cm-2 at 1.23 V vs. reversible hydrogen electrode under AM 1.5 G illumination, as well as the dihydroxyacetone selectivity from 54.0% to 80.3%, finally achieving a dihydroxyacetone production rate of 361.9 mmol m-2 h-1 that outperforms all reported values. The surface atom customization opens a way to regulate the solar-driven organic transformation pathway toward a carbon chain-balanced product.

In-situ Bi-modified Pt towards glycerol and formic acid electro-oxidation: Effects of catalyst structure and surface microenvironment on activity and selectivity

The performances of glycerol electro-oxidation reaction (GOR) and formic acid electro-oxidation reaction (FAOR) catalyzed by Pt catalyst were dramatically improved by adding Bi3+ into the reaction solution. The dynamic structure and microenvironment of in-situ Bi-modified Pt and their impact on the catalytic performances were revealed. A strong correlation was established between the Bi coverage of Pt-based catalysts and their resistance to CO poisoning and performance in GOR and FAOR. When Bi3+ increased to a certain amount, a Bi-shell containing hydroxides was formed on Pt surfaces except the formation of Pt-Bi ensemble. On Pt catalyst covered with 43.9 % Bi, the peak mass-specific activities of GOR and FAOR in forward scans were 4.2 and 34.7 times that of Pt/NCNTs, respectively. The peak electrochemical active surface area (ECSA)-specific activity of FAOR in forward scan for Pt with 52.6 % Bi coverage was 80.6 times that of Pt/NCNTs. The dehydrogenation process in FAOR and the 4-electron pathway in GOR were improved for Bi-modified Pt. The experimental results and DFT calculations indicated that the positively charged Bi and structure of Pt-Bi ensemble improved the adsorption and interaction of negatively charged intermediates, and the enhanced hydroxides facilitated the oxidation and removal of toxic intermediates, such as CO.

Dihydroxyacetone production by glycerol oxidation under moderate condition using Pt loaded on La1-xBixOF solids

Pt/La_1-xBi_xOF/SBA-16 (SBA-16: Santa Barbara Amorphous no. 16) catalysts were prepared to produce dihydroxyacetone (DHA) from glycerol under moderate conditions. By using 7 wt% Pt/16 wt% La_0.95Bi_0.05OF/SBA-16, the DHA yield reached up to 78.4% (glycerol conversion: 100%) after reacting for 6 h at 30 °C in an atmospheric open-air system.

Highly Selective Transformation of Biomass Derivatives to Valuable Chemicals by Single-Atom Photocatalyst Ni/TiO2

Selective CC cleavage of the biomass derivative glycerol under mild conditions is recognized as a promising yet challenging synthesis route to produce value-added chemicals. Here, a highly selective catalyst for the transformation of glycerol to the high-value product glycolaldehyde is presented, which is composed of nickel single atoms confined to the surface of titanium dioxide. Driven by light, the catalyst operates under ambient conditions using air as a green oxidant. The optimized catalyst shows a selectivity of over 60% to glycolaldehyde, resulting in 1058 µmol g_Cat ^-1  h^-1 production rate, and ≈3 times higher turnover number than NiO_x -nanoparticle-decorated TiO₂ photocatalyst. Diverse operando and in situ spectroscopies unveil the unique function of the Ni single atom, which can significantly promote oxygen adsorption, work as an electron sink, and accelerate the production of superoxide radicals, thereby improving the selectivity toward glycolaldehyde over other by-products.

Promoting Electrocatalytic Hydrogenation of Oxalic Acid to Glycolic Acid via an Al3+ Ion Adsorption Strategy Coupled with Ethylene Glycol Oxidation

Electrocatalytic hydrogenation (ECH) of oxalic acid (OX) to produce glycolic acid (GA), an important building block of biodegradable polymers as well as application in various branches of chemistry, has attracted extensive attention in the industry, while it still encounters challenges of low reaction rate and selectivity. Herein, we reported a cation adsorption strategy to realize the efficient ECH of OX to GA by adsorbing Al³⁺ ions on an anatase titanium dioxide (TiO₂) nanosheet array, achieving 2-fold enhanced GA productivity (1.3 vs 0.65 mmol cm^-2 h^-1) with higher Faradaic efficiency (FE) (85 vs 69%) at -0.74 V vs RHE. We reveal that the Al³⁺ adatoms on TiO₂ both act as electrophilic adsorption sites to enhance the carbonyl (C═O) adsorption of OX and glyoxylic acid (intermediate) and also promote the generation of reactive hydrogen (H*) on TiO₂, thus promoting the reaction rate. This strategy is demonstrated effective for different carboxylic acids. Furthermore, we realized the coproduction of GA at the bipolar of a H-type cell by pairing ECH of OX (at cathode) and electrooxidation of ethylene glycol (at anode), demonstrating an economical manner with maximum electron economy.

Maneuvering the Peroxidase-Like Activity of Palladium-Based Nanozymes by Alloying with Oxophilic Bismuth for Biosensing

Engineering the catalytic performance of nanozymes is of vital importance for their broad applications in biological analysis, cancer treatment, and environmental management. Herein, a strategy to boost the peroxidase-like activity of Pd-based nanozymes with oxophilic metallic bismuth (Bi) is demonstrated, which is based on the incorporation of oxophilic Bi in the Pd-based alloy nanocrystals (NCs). To synthesize PdBi alloy NCs, a seed-mediated method is employed with the assistance of underpotential deposition (UPD) of Bi on Pd. The strong interaction of Bi atoms with Pd surfaces favors the formation of alloy structures with controllable shapes and excellent monodispersity. More importantly, the PdBi NCs show excellent peroxidase-like activities compared with pristine Pd NCs. The structure-function correlations for the PdBi nanozymes are elucidated, and an indirect colorimetric method based on cascade reactions to determine alkaline phosphatase (ALP) is established. This method has good linear range, low detection limit, excellent selectivity, and anti-interference. Collectively, this work not only provides new insights for the design of high-efficiency nanozymes, expands the colorimetric sensing platform based on enzyme cascade reactions, but also represents a new example for UPD-directed synthesis of alloy NCs.

Chemicals Production from Glycerol through Heterogeneous Catalysis: A Review

Utilization of biofuels generated from renewable sources has attracted broad attention due to their benefits such as reducing consumption of fossil fuels, sustainability, and consequently prevention of global warming. The production of biodiesel causes a huge amount of by-product, crude glycerol, to accumulate. Glycerol, because of its unique structure having three hydroxyl groups, can be converted to a variety of industrially valuable products. In recent decades, increasing studies have been carried out on different catalytic pathways to selectively produce a wide range of glycerol derivatives. In the current review, the main routes including carboxylation, oxidation, etherification, hydrogenolysis, esterification, and dehydration to convert glycerol to value-added products are investigated. In order to achieve more glycerol conversion and higher desired product selectivity, acquisition of knowledge on the catalysts, the type of acidic or basic, the supports, and studying various reaction pathways and operating parameters are necessary. This review attempts to summarize the knowledge of catalytic reactions and mechanisms leading to value-added derivatives of glycerol. Additionally, the application of main products from glycerol are discussed. In addition, an overview on the market of glycerol, its properties, applications, and prospects is presented.

Electrochemical Study of Semiconductor Properties for Bismuth Silicate-Based Photocatalysts Obtained via Hydro-/Solvothermal Approach

Three bismuth silicate-based photocatalysts (composites of Bi₂SiO₅ and Bi₁₂SiO₂₀) prepared via the hydro-/solvothermal approach were studied using electrochemical methods. The characteristic parameters of semiconductors, such as flat band potential, donor density, and mobility of their charge carriers, were obtained and compared with the materials’ photocatalytic activity. An attempt was made to study the effect of solution components on the semiconductor/liquid interface (SLI). In particular, the Mott–Schottky characterization was made in a common model electrolyte (Na₂SO₄) and with the addition of glycerol as a model organic compound for photocatalysis. Thus, a medium close to those in photocatalytic experiments was simulated, at least within the limits allowed by electrochemical measurements. Zeta-potential measurements and electrochemical impedance spectroscopy were used to reveal the processes taking place at the SLI. It was found that the medium in which measurements were carried out dramatically impacted the results. The flat band potential values (E_fb) obtained via the Mott–Schottky technique were shown to differ significantly depending on the solution used in the experiment, which is explained by different processes taking place at the SLI. A strong influence of specific adsorption of commonly used sulfate ions and neutral molecules on the measured values of E_fb was shown.

Semi-quantitative design of synergetic surficial/interfacial sites for the semi-continuous oxidation of glycerol

Qualitatively identifying the dominant catalytic site for each step of a semi-continuous reaction and semi-quantitatively correlating such different sites to the catalytic performance is of great significance toward the integration of multiple well-optimized sites on a heterogeneous catalyst. Herein, a series of structurally defined TiOx-based catalysts were synthesized to provide a feasible approach to investigate the aforementioned issues using the semi-continuous oxidation of glycerol as a model reaction. Detailed investigations have verified the simultaneous presence of two kinds of Pt active sites: 1) Negatively charged Pt bound to the oxygen vacancies of modified TiOx in the form of Ptδ--Ov-Ti3+ sites and 2) metallic Pt (Pt0 site) located away from the interface. Meanwhile, the proportion of surficial and interfacial sites varies over this series of catalysts. Combined in situ FTIR experiments revealed that the reaction network was well-tuned via a site cooperation mechanism: The surficial Pt0 sites dissociatively adsorb the OH group of glycerol with a monodentate bonding geometry and the Ptδ--Ov-Ti3+ sites dissociate the C=O bond of the aldehyde group in a bidentate form. Furthermore, CO-FTIR spectroscopy confirmed a correlation between the reaction rate/product selectivity and the fraction of surficial/interfacial sites. A rational proportion of surficial and interfacial sites is key to enabling a high yield of glyceric acid. The most active catalyst with 32% surface sites and 68% interfacial sites exhibited 90.0% glycerol conversion and 68.5% GLYA selectivity. These findings provide a deeper understanding of the structure-activity relationships using qualitative identification and semi-quantitative analysis.

Production of Hydroxypyruvic Acid by Glycerol Oxidation over Pt/CeO2-ZrO2-Bi2O3-PbO/SBA-16 Catalysts

Pt/CeO2-ZrO2-Bi2O3-PbO/SBA-16 (SBA-16: Santa Barbara Amorphous No. 16) catalysts were synthesized to produce hydroxypyruvic acid by glycerol oxidation. In the catalysts, the introduction of PbO into CeO2-ZrO2-Bi2O3 improved the oxygen release and storage abilities owing to the synergistic redox reaction of Pb2+/4+ and Ce3+/4+, which facilitated the oxidation ability of Pt. In addition, the oxidation of the secondary OH group in glycerol might be accelerated by the geometric effects of glycerol, Pt, and Bi3+ or Pb2+/4+. Furthermore, the moderate reaction conditions such as room temperature and open-air atmosphere enabled the suppression of further oxidation of hydroxypyruvic acid. The highest catalytic activity was obtained for 7 wt% Pt/16 wt% Ce0.60Zr0.15Bi0.20Pb0.05O2−δ/SBA-16, which provided a hydroxypyruvic acid yield maximum of 24.6%, after the reaction for 6 h at 30 °C in atmospheric air.

Unique structure of active platinum-bismuth site for oxidation of carbon monoxide

As the technology development, the future advanced combustion engines must be designed to perform at a low temperature. Thus, it is a great challenge to synthesize high active and stable catalysts to resolve exhaust below 100 °C. Here, we report that bismuth as a dopant is added to form platinum-bismuth cluster on silica for CO oxidation. The highly reducible oxygen species provided by surface metal-oxide (M-O) interface could be activated by CO at low temperature (~50 °C) with a high CO2 production rate of 487 μmolCO2·gPt-1·s-1 at 110 °C. Experiment data combined with density functional calculation (DFT) results demonstrate that Pt cluster with surface Pt-O-Bi structure is the active site for CO oxidation via providing moderate CO adsorption and activating CO molecules with electron transformation between platinum atom and carbon monoxide. These findings provide a unique and general approach towards design of potential excellent performance catalysts for redox reaction.

An Overview of Glycerol Electrooxidation Mechanisms on Pt, Pd and Au

In the most recent decade, glycerol electrooxidation (GEOR) has attracted extensive research interest for valorization of glycerol: the conversion of glycerol to value-added products. These reactions at platinum, palladium, and gold electrodes have a lot of uncertainty in their reaction mechanisms, which has generated some controversies. This review gathers many reported experimental results, observations and proposed reaction mechanisms in order to draw a full picture of GEOR. A particular focus is the clarification of two propositions: Pd is inferior to Pt in cleaving the C-C bonds of glycerol during the electrooxidation and the massive production of CO₂ at high overpotentials is due to the oxidation of the already-oxidized carboxylate products. It is concluded that the inferior C-C bond cleavability with Pd electrodes, as compared with Pt electrodes, is due to the inefficiency of deprotonation, and the massive generation of CO₂ as well as other C1/C2 side products is partially caused by the consumption of OH^- at the anodes, as a lower pH reduces the amount of carboxylates and favors the C-C bond scission. A reaction mechanism is proposed in this review, in which the generation of side products are directly from glycerol ("competition" between each side product) rather than from the further oxidation of C2/C3 products. Additionally, GEOR results and associated interpretations for Ni electrodes are presented, as well as a brief review on the performances of multi-metallic electrocatalysts (most of which are nanocatalysts) as an introduction to these future research hotpots.

Efficiently selective oxidation of glycerol by BiQDs/BiOBr–Ov: promotion of molecular oxygen activation by Bi quantum dots and oxygen vacancies

Bi_QDs and O_v can promote the activation of O₂ to make Bi_QDs/BiOBr–O_v catalyze the selective oxidation of glycerol efficiently.