Hetropolyacid-Catalyzed Oxidation of Glycerol into Lactic Acid under Mild Base-Free Conditions

Recent Progress on Functionalized Nanoporous Heteropoly Acids: From Synthesis to Applications

Functionalized nanoporous heteropoly acids (HPAs) have garnered significant attention in recent years due to their enhanced surface area and porosity, as well as their potential for low-cost regeneration compared to bulk materials. This review aims to provide an overview of the recent advancements in the synthesis and applications of functionalized HPAs. We begin by introducing the fundamental properties of HPAs and their unique structure, followed by a comprehensive overview of the various approaches employed for the synthesis of functionalized HPAs, including salts, anchoring onto supports, and implementing mesoporous silica sieves. The potential applications of functionalized HPAs in various fields are also discussed, highlighting their boosted performance in a wide range of applications. Finally, we address the current challenges and present future prospects in the development of functionalized HPAs, particularly in the context of mesoporous HPAs. This review aims to provide a comprehensive summary of the recent progress in the field, highlighting the significant advancements made in the synthesis and applications of functionalized HPAs.

A review of the catalytic conversion of glycerol to lactic acid in the presence of aqueous base

Lactic acid is a high-value-added chemical with large production, which is used in many industries including the production of pyruvic and acrylic acids. Lactic acid is largely obtained from the oxidation of glycerol, which is a prevalent by-product of biodiesel production. However, the oxidation of glycerol to lactic acid requires harsh reaction conditions such as high temperature and pressure as well as the use of a hefty strong base. In the presence of suitable catalysts, the production of lactic acid from glycerol can be achieved under mild conditions with 1 equivalent base per mole of glycerol. Herein, we review the reports of the catalytic conversion of glycerol to lactic acid in an aqueous alkaline medium considering the reaction conditions, catalytic activity for glycerol conversion and selectivity for lactic acid. We start first with the reports on the use of homogeneous catalysts that have high catalytic activity but miserable recovery. Next, we discuss the employment of colloidal metal(0) nanoparticles as catalysts in glycerol oxidation. The papers on the use of supported metal(0) nanoparticles are reviewed according to the type of support. We then review the polymetallic and metal/metal oxide nanocatalysts used for the conversion of glycerol to lactic acid in an alkaline medium. The catalysts tested for glycerol conversion to lactic acid without any additional bases are also discussed to emphasize the importance of a strong base for catalytic performance. The proposed mechanisms of glycerol oxidation to lactic acid in the presence or absence of catalysts as well as for the formation of side products are discussed. The available experimental kinetics data are shown to fit the mechanism with the formation of glyceraldehyde from glycerol alkoxide as the rate-determining step.

Fabrication of ordered mesoporous POMs/SiO2-NH2 nanofibers for production of DFF from 5-HMF for cellulose wastewater resource recovery

5-hydroxymethylfurfural (5-HMF) is a biomass cellulose platform product that can be transformed into the valuable resource 2,5-diformylfuran (DFF). Polyoxometalates (POMs) have important applications in resource recovery technologies and cellulose wastewater treatment. Ordered mesoporous H₅PMo₁₀V₂O₄₀/SiO₂-NH₂ (wt%) nanofibers (HPMoV/meso-SiO₂-NH₂ (wt%)) were synthesized by the combining in-situ fabrication and electrospinning techniques, using H₅PMo₁₀V₂O₄₀ (HPMoV) and organic-silica as precursors. Aiming the recovery and transformation of 5-HMF, aerobic oxidation of 5-HMF was explored using these nanofibers as catalysts, while the best yield of DFF (90.0%) was obtained upon HPMoV/meso-SiO₂-NH₂ (23%) nanofibers after 8 h at 120 °C using oxygen (1.0 MPa). The selectivity to DFF was improved by changing the hydrophilicity of the HPMoV@SiO₂ nanofibers to hydrophobicity by modifying SiO₂ nanofibers with -NH₂R compared to mesoporous SiO₂ nanofibers, which allowed the formed DFF to be isolated. In the recycling test, HPMoV@SiO₂-NH₂ showed good performance, and no leaching of active sites from SiO₂-NH₂ due to the interactions between them occurred after 10 cycles. The production of DFF from the real cellulosic wastewater was obtained with 118% yield based on 5-HMF conversion by HPMoV/meso-SiO₂-NH₂ (23) and oxygen, which was contributed to the one-pot conversion of sugar, furan and 5-HMF in the wastewater.

Advances in catalytic routes for the production of carboxylic acids from biomass: a step forward for sustainable polymers

Polymers are ubiquitously present in our daily life because they can meet a wide range of needs and fields of applications. This success, based on an irresponsible linear consumption of plastics and the access to cheap oil, is creating serious environmental problems. Two lines of actions are needed to cope with them: to adopt a circular consumption of plastics and to produce renewable carbon-neutral monomers. This review analyses the recent advances in the chemocatalytic processes for producing biomass-derived carboxylic acids. These renewable carboxylic acids are involved in the synthesis of relevant general purpose and specialty polyesters and polyamides; some of them are currently derived from oil, while others can become surrogates of petrochemical polymers due to their excellent performance properties. Polyesters and polyamides are very suitable to be depolymerised to other valuable chemicals or to their constituent monomers, what facilitates the circular reutilisation of these monomers. Different types of carboxylic acids have been included in this review: monocarboxylic acids (like glycolic, lactic, hydroxypropanoic, methyl vinyl glycolic, methyl-4-methoxy-2-hydroxybutanoic, 2,5-dihydroxypent-3-enoic, 2,5,6-trihydroxyhex-3-enoic acids, diphenolic, acrylic and δ-amino levulinic acids), dicarboxylic acids (2,5-furandicarboxylic, maleic, succinic, adipic and terephthalic acids) and sugar acids (like gluconic and glucaric acids). The review evaluates the technology status and the advantages and drawbacks of each route in terms of feedstock, reaction pathways, catalysts and economic and environmental evaluation. The prospects and the new research that should be undertaken to overcome the main problems threatening their economic viability or the weaknesses that prevent their commercial implementation have also been underlined.

A Polyoxometalate Composite Based on Hierarchical MIL-101 with Enhanced Catalytic Activity in Methanolysis of Styrene Oxide

A new efficient polyoxometalate composite catalyst of hierarchical MIL-101 and phosphotungstic acid (PTA) was facilely prepared by the immersion method. The material was thoroughly characterized by powder x-ray diffraction (PXRD), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX) and inductively coupled plasma‒optical emission spectrometry (ICP-OES). Compared to the pristine nonhierarchical MIL-101 composite, the hierarchical composite demonstrated much higher catalytic performance in methanolysis of styrene oxide, such as catalytic activity and reusability.

Selective oxidation of 1,2-propanediol to lactic acid over Cu-modified Au/hydrotalcite catalysts

1,2-Propanediol was converted to lactic acid over Cu-modified Au/hydrotalcite catalysts with high conversion and selectivity.

Heterogenization of polyoxometalates as solid catalysts in aerobic oxidation of glycerol

A series of heterogeneous catalysts LnPMo₁₂O₄₀ (L = Al³⁺, Fe³⁺, Cr³⁺, Ti⁴⁺, Zr⁴⁺, Zn²⁺) and HxPMo₁₁LO₃₉ (L = Zn²⁺, Cr³⁺, Fe³⁺, Al³⁺, Ti⁴⁺) were prepared using a simple calcination treatment and were evaluated in aerobic oxidation of glycerol.

Sustainable production of pyruvic acid: oxidative dehydrogenation of lactic acid over the FeMoO/P catalyst

Novel redox of FeMoO/P by electron transfer between Fe and Mo is favorable for the oxidative dehydrogenation of lactic acid.

The fabrication of trifunctional polyoxometalate hybrids for the cascade conversion of glycerol to lactic acid

Lactic acid (LA) has been produced with cascade reactions under non-noble metal and base-free conditions.

A Polyoxometalate-Based Microfluidic Device for Liquid-Phase Oxidation of Glycerol

Peroxidation of glycerol has been carried out in a polyoxometalate (POM)-based microfluidic reactor, which was fabricated on a capillary by using a layer-by-layer strategy. Lactic acid (LA) is produced selectively in high yield with a TOF as high as 20 000 h^-1 , compared to a TOF of 200 h^-1 in batch mode. This POM microfluidic reactor is readily prepared, scalable, highly stable, reusable, and also potentially applicable to selective oxidation of other bio-wastes.

Highly Efficient Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid with Heteropoly Acids and Ionic Liquids

2,5-Furandicarboxylic acid (FDCA) is regarded as an important bioderived substitute for petrochemically derived terephthalic acid (PTA), which is widely applied in the polymer industry. This work delineates the base-free oxidation of 5-hydroxymethylfurfural (HMF) to FDCA in an ionic liquid/heteropoly acid (IL-HPA) catalytic system. HPAs displayed high activity for selective oxidation; their active center (Mo/V) was activated by O₂ and transformed from oxygen single and double bonds to epoxy groups, resulting in an FDCA yield of 89 % for HPMV₆ (HPM=H₃ PMo₁₂ O₄₀ ) in the presence of [Bmim]Cl (1-butyl-3-methylimidazolium chloride) under optimized reaction conditions. The high solubility of imidazole ILs for FDCA improved the affinity of HMF and the active centers of the catalyst and protected the furan ring from oxidative cleavage. Furthermore, multiple hydrogen bonds simultaneously formed between the electronegative anions and hydroxy protons of HMF, as well as the hydrogen atoms of the imidazole rings and hydroxy groups, promoting the transformation to aldehyde groups. Various starting materials were studied, and a moderate FDCA yield was obtained from glucose. This work provides an interesting IL-HPA catalytic system for the base-free synthesis of FDCA from accessible monosaccharides and illustrates the great potential of FDCA production from renewable carbohydrates.

Incorporation of Ce3+ ions into dodecatungstophosphoric acid for the production of biodiesel from waste cooking oil

A series of cerium-exchanged dodecatungstophosphates Ce_xH_3-3xPW₁₂O₄₀ (Ce_xH_3-3xPW, x = 0.4, 0.6, 0.7, 0.8, 0.9, and 1.0) were designed and characterized by Fourier transform infrared spectroscopy (FT-IR), pyridine adsorption IR spectra, X-ray diffraction (XRD), and temperature programmed desorption of ammonia (NH₃-TPD). The activity of these catalysts was evaluated for the generation of biodiesel from waste cooking oil (WCO) with 27 wt% of free fatty acids (FFAs) and 1 wt% of water. Compared to theri parent H₃PW₁₂O₄₀, Ce_xH_3-3xPW showed higher activity for esterification of FFAs and transesterification of triglyceride to mono-alkyl esters of fatty acids (FAMEs) in one-pot. The acidic properties of Ce_xH_3-3xPW depended on the amount of Ce³⁺ ions in the secondary structure of Keggin heteropolyacids, while conversion of triglycerides and FFAs depended on their increasing acid contents. Among Ce_xH_3-3xPW, Ce_0.7H_0.9PW showed significant activity due to its high Brønsted acidity and Lewis acidity with 98% conversion of WCO and almost 100% selectivity to FAME at the molar ratio of methanol to WCO = 21:1 and 65 °C for 12 h. The reaction adhered to first-order kinetics with the activation energy (Ea) of 71 kJ/mol and the frequency factor (A) of 1.8 × 10⁸ min^-1, while the reaction rates were not influenced by the internal mass transport. The catalyst behaved as a heterogeneous catalyst, which can achieve the regeneration and be used more than five runs but without obvious decrease in activity. The characteristics of the WCO methyl ester were found to be close to the engine requirement.

Designation of highly efficient catalysts for one pot conversion of glycerol to lactic acid

Production of lactic acid from glycerol is a cascade catalytic procedure using multifunctional catalysts combined with oxidative and acidic catalytic sites. Therefore, a series of silver-exchanged phosphomolybdic acid catalysts (Ag_xH_3−xPMo₁₂O₄₀, x = 1 ~ 3, abbreviated as Ag_xPMo) was designed and applied in glycerol oxidation with O₂ as an oxidant to produce lactic acid (LA) without adding any base. Among all, total silver exchanged phosphomolybdic acid (Ag₃PMo) was found to be the most active one with LA selectivity of 93% at 99% conversion under mild conditions of 5 h at 60 °C. The exceptionally high efficiency was contributed to the generation of strong Lewis acid sites, enhanced redox potentials and water-tolerance. More importantly, Ag₃PMo was tolerant in crude glycerol from biodiesel production. And the reaction mechanism was also discussed. Meanwhile, Ag₃PMo acted as a heterogeneous catalyst for 12 recycles without loss of activity.