A review of aerobic glycerol oxidation processes using heterogeneous catalysts: a sustainable pathway for the production of dihydroxyacetone

Aerobic Oxidative Synthesis of Formamides from Amines and Bioderived Formyl Surrogates

Herein we present a new strategy for the oxidative synthesis of formamides from various types of amines and bioderived formyl sources (DHA, GLA and GLCA) and molecular oxygen (O2) as oxidant on g-C3N4 supported Cu catalysts. Combined characterization data from EPR, XAFS, XRD and XPS revealed the formation of single CuN4 sites on supported Cuphen/C3N4 catalysts. EPR spin trapping experiments disclosed ⋅OOH radicals as reactive oxygen species and ⋅NR1R2 radicals being responsible for the initial C-C bond cleavage. Control experiments and DFT calculations showed that the successive C-C bond cleavage in DHA proceeds via a reaction mechanism co-mediated by ⋅NR1R2 and ⋅OOH radicals based on the well-equilibrated CuII and CuI cycle. Our catalyst has much higher activity (TOF) than those based on noble metals.

Converting Glycerol into Valuable Trioses by Cuδ+ -Single-Atom-Decorated WO3 under Visible Light

Photocatalytic selective oxidation under visible light presents a promising approach for the sustainable transformation of biomass-derived wastes. However, achieving both high conversion and excellent selectivity poses a significant challenge. In this study, two valuable trioses, glyceraldehyde and dihydroxyacetone, are produced from glycerol over Cuδ+ -decorated WO3 photocatalyst in the presence of H2 O2 . The photocatalyst exhibits a remarkable five-fold increase in the conversion rate (3.81 mmol ⋅ g-1  ⋅ h-1 ) while maintaining a high selectivity towards two trioses (46.4 % to glyceraldehyde and 32.9 % to dihydroxyacetone). Through a comprehensive analysis involving X-ray photoelectron spectroscopy measurements with and without light irradiation, electron spin resonance spectroscopy, and isotopic analysis, the critical role of Cu+ species has been explored as efficient hole acceptors. These species facilitate charge transfer, promoting glycerol oxidation by photoholes, followed by coupling with OH- , which are subsequently dehydrated to yield the desired glyceraldehyde and dihydroxyacetone.

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.

Dihydroxyacetone: A User Guide for a Challenging Bio-Based Synthon

1,3-dihydroxyacetone (DHA) is an underrated bio-based synthon, with a broad range of reactivities. It is produced for the revalorization of glycerol, a major side-product of the growing biodiesel industry. The overwhelming majority of DHA produced worldwide is intended for application as a self-tanning agent in cosmetic formulations. This review provides an overview of the discovery, physical and chemical properties of DHA, and of its industrial production routes from glycerol. Microbial fermentation is the only industrial-scaled route but advances in electrooxidation and aerobic oxidation are also reported. This review focuses on the plurality of reactivities of DHA to help chemists interested in bio-based building blocks see the potential of DHA for this application. The handling of DHA is delicate as it can undergo dimerization as well as isomerization reactions in aqueous solutions at room temperature. DHA can also be involved in further side-reactions, yielding original side-products, as well as compounds of interest. If this peculiar reactivity was harnessed, DHA could help address current sustainability challenges encountered in the synthesis of speciality polymers, ranging from biocompatible polymers to innovative polymers with cutting-edge properties and improved biodegradability.

Catalytic Oxidation of Glycerol over Pt Supported on MOF-Derived Carbon Nanosheets

A series of nitrogen-doped porous carbon nanosheets (NPCNs) doped with transition-metal-supported Pt catalysts were prepared by colloidal deposition and evaluated for the selective oxidation of glycerol to glyceric acid (GLYA) under nonalkaline conditions. The transition metal contained in the catalyst was found to affect its performance and selectivity for GLYA, with the Pt/Zr@NPCN catalyst showing the highest catalytic activity and selectivity. These materials were characterized using Brunauer-Emmett-Teller surface area analysis, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and CO₂ temperature-programmed desorption. The results showed that the small size of the Pt nanoparticles, the interaction between the Pt nanoparticles and the support, and the unique textural properties of the catalyst all promoted glycerol conversion and GLYA selectivity. A Zr concentration of 1.5 wt % and a support preparation temperature of 800 °C were found to provide a catalyst with the optimal performance that exhibited a glycerol conversion and selectivity for GLYA of 68.62 and 77.29%, respectively, at an initial O₂ pressure of 10 bar and 60 °C after 6 h. Even after being recycled five times, this material provided a GLYA selectivity of approximately 75%, although the glycerol conversion decreased from 68 to 50%. The insights may provide new suggestions on the design of efficient support for the selective oxidation of polyols.

Chemoenzymatic conversion of glycerol to lactic acid and glycolic acid

Catalytic valorization of raw glycerol derived from biodiesel into high-value chemicals has attracted great attention. Here, we report chemoenzymatic cascade reactions that convert glycerol to lactic acid and glycolic acid. In the enzymatic step, a coenzyme recycling system was developed to convert glycerol into 1,3-dihydroxyacetone (DHA) with a yield of 92.3% in potassium phosphate buffer (300 mM, pH 7.1) containing 100 mM glycerol, 2 mM NAD+, 242 U/mL glycerol dehydrogenase-GldA and NADH oxidase-SpNoxK184R at 30 °C. Subsequently, NaOH or NaClO2 catalyzes the formation of lactic acid and glycolic acid from DHA. The high yield of lactic acid (72.3%) and glycolic acid (78.2%) verify the benefit of the chemoenzymatic approaches.

Unraveling Unique Surface Chemistry of Transition Metal Nitrides in Controlling Selective C-O Bond Scission Pathways of Glycerol

Controlled C-O bond scission is an important step for upgrading glycerol, a major byproduct from the continuously increasing biodiesel production. Transition metal nitride catalysts have been identified as promising hydrodeoxygenation (HDO) catalysts, but fundamental understanding regarding the active sites of the catalysts and reaction mechanism remains unclear. This work demonstrates a fundamental surface science study of Mo₂N and Cu/Mo₂N for the selective HDO reaction of glycerol, using a combination of model surface experiments and first-principles calculations. Temperature-programmed desorption (TPD) experiments showed that clean Mo₂N cleaved two or three C-O bonds of glycerol to produce allyl alcohol, propanal, and propylene. The addition of Cu to Mo₂N changed the reaction pathway to one C-O bond scission to produce acetol. High-resolution electron energy loss spectroscopy (HREELS) results identified the surface intermediates, showing a facile C-H bond activation on Mo₂N. Density functional theory (DFT) calculations revealed that the surface N on Mo₂N interacted with the H atoms in glycerol and blocked some Mo sites to enable selective C-O bond scission. This work shows that Mo₂N and Cu/Mo₂N are active and selective for the controlled C-O bond scission of glycerol and in turn provides insights into the rational catalyst design for selective oxygen removal of relevant biomass-derived oxygenates.

Synthesis and Characterization of Supported Pd Catalysts for Potential Application in Glycerol Electro-Oxidation

Ceria-supported Pd catalysts encompassing oxides of Cu, Co, and Fe were synthesized and characterized using XRD, TEM, SEM-EDX, TPR, BET, and Raman. After the incorporation of the metal oxides, the surface area and pore volume of the ceria support decreased. XRD showed the presence of the metal oxide phases as well as the support, CeO2. TPR showed that the bimetallic catalyst had improved reducibility compared to the monometallic Pd/CeO2. TEM images showed irregular-shaped particles with an average size distribution of 2–10 nm. SEM-EDX showed that the metal oxides were evenly distributed over the surface of the support. The electro-oxidation of glycerol in an alkaline environment was evaluated using cyclic voltammetry, and the products formed were identified and quantified using GC-MS. Glyceric acid was the dominant product over Pd-CuO/CeO2, while glyceraldehyde and dihydroxyacetone were dominant over Pd-Co3O4/CeO2 and Pd-Fe2O3/CeO2, respectively.

Catalytic Conversion of Glycerol to Methyl Lactate over Au-CuO/Sn-Beta: The Roles of Sn-Beta

The production of methyl lactate as a degradable polymer monomer from biomass was an important topic for a sustainable society. In this manuscript, glycerol was oxidated to methyl lactate catalyzed by the combination of Au-CuO and Sn-Beta. The influence of Sn content, Sn source, and the preparation conditions for Sn-β was studied. The Au content in Au/CuO was also investigated by varying the Au content in Au/CuO. The catalysts were characterized by XRD, FTIR spectroscopy of pyridine adsorption, and TEM to study the role of Sn and the influence of different parameters for catalyst preparation. After the optimization of reaction parameters, the yield of methyl lactate from glycerol reached 59% at 363 K after reacting in 1.6 MPa of O2 for 6 h.

1,2—Propanediol Production from Glycerol Derived from Biodiesel’s Production: Technical and Economic Study

For every nine tons of produced biodiesel, there is another ton of glycerol as a byproduct. Therefore, glycerol prices dropped significantly worldwide in recent years; the more significant biodiesel production is, the more glycerol exists as a byproduct. glycerol prices also impact the biodiesel manufacturing business, as it could be sold according to its refinement grade. The primary objective of this work was to evaluate the economic potential of the production of 1,2-propanediol derived from the biodiesel produced in Colombia. A plant to produce 1,2-propanediol via catalytic hydrogenation of glycerol in a trickle-bed reactor was designed. The plant comprised a reaction scheme where non-converted excess hydrogen was recycled, and the heat generated in the reactor was recovered. The reactor effluent was sent to a separation train where 98% m/m purity 1,2-propanediol was attained. Capital and operational costs were estimated from the process simulation. The net present value (NPV) and the modified internal return rate (MIRR) of the plant were used to assess the viability of the process. Their sensitivity to key input variables was evaluated to find the viability limits of the project. The economic potential of the 1,2-propanediol was calculated in USD 1.2/kg; for the base case, the NPV and the MIRR were USD 54.805 million and 22.56%, respectively, showing that, for moderate variations in products and raw material prices, the process is economically viable.

Versatile Coordination Polymer Catalyst for Acid Reactions Involving Biobased Heterocyclic Chemicals

The chemical valorization/repurposing of biomass-derived chemicals contributes to a biobased economy. Furfural (Fur) is a recognized platform chemical produced from renewable lignocellulosic biomass, and furfuryl alcohol (FA) is its most important application. The aromatic aldehydes Fur and benzaldehyde (Bza) are commonly found in the slate of compounds produced via biomass pyrolysis. On the other hand, glycerol (Gly) is a by-product of the industrial production of biodiesel, derived from fatty acid components of biomass. This work focuses on acid catalyzed routes of Fur, Bza, Gly and FA, using a versatile crystalline lamellar coordination polymer catalyst, namely [Gd(H4nmp)(H2O)2]Cl·2H2O (1) [H6nmp=nitrilotris(methylenephosphonic acid)] synthesized via an ecofriendly, relatively fast, mild microwave-assisted approach (in water, 70 °C/40 min). This is the first among crystalline coordination polymers or metal-organic framework type materials studied for the Fur/Gly and Bza/Gly reactions, giving heterobicyclic products of the type dioxolane and dioxane, and was also effective for the FA/ethanol reaction. 1 was stable and promoted the target catalytic reactions, selectively leading to heterobicyclic dioxane and dioxolane type products in the Fur/Gly and Bza/Gly reactions (up to 91% and 95% total yields respectively, at 90 °C/4 h), and, on the other hand, 2-(ethoxymethyl)furan and ethyl levulinate from heterocyclic FA.