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The investigation carried out in this study focused on exploring the hydrogen bonding structure of liquid solutions of methyl lactate and 1-alkanols include 1-butanol, 1-pentanol, 1-hexanol, and 1-heptanol. To analyze the interactions between the molecules, the researcher utilized the cubic-plus-association (CPA) model, which takes into account both the physical and association interactions. The maximum deviation observed in the density of the liquid solutions of methyl lactate with 1-heptanol was 0.28%, indicating the effectiveness of the CPA model in accurately modeling the density. Additionally, the researchers calculated the excess molar volumes and deviation in viscosity for the studied liquid mixtures. The analysis of these measurements revealed that the solutions of methyl lactate with 1-alkanols exhibited positive excess molar volumes across the entire concentration range. On the other hand, negative viscosity deviations were observed for the mentioned alkanols. These findings suggest that there are weak intermolecular associations within the liquid solutions, with weaker bond strength observed in higher alkanols. [ABSTRACT FROM AUTHOR]

Transformation of methyl lactate to acrylic acid was investigated over Ca3(PO4)2, Ca2(P2O7) and their mixture in the temperature range of 250-425 °C. The initial concentration of methyl lactate in water was varied from 2 wt% to neat methyl lactate. The results showed that these phosphate catalysts did not contain any measurable amounts of either acid sites or basic sites. The best catalyst was Ca3(PO4)2 giving 62% selectivity to acrylic acid at 75% conversion at 400 °C using GHSV of 95280 h−1 and 2 wt% methyl lactate in the initial feed. This catalyst exhibited larger surface area in comparison to Ca2(P2O7). Elemental analysis revealed that some Ca leaching occurred during reaction, while in case of Ca2(P2O7) the calcium leaching was 3.4 fold higher than observed for Ca3(PO4)2. Long-term results over Ca3(PO4)2 showed that extensive catalyst deactivation occurred during the first 11 h time-on-stream, after which the activity dropped only slightly. In addition to kinetic studies with different parameters, also, kinetic modeling was performed and the activation energies for formation of different products were determined over different catalysts. [ABSTRACT FROM AUTHOR]

The development of catalytic methods for xylose transformation as renewable raw material into value-added chemicals such as lactic and glycolic acid esters has been the subject of intensive research in recent years. Thus, methyl lactate and methyl glycolate are used as a starting material for the production of lactide and glycolide – an important monomers for the production of biodegradable polymers. The aim of this work was to search of simple effective catalyst for transformation of xylose into methyl esters of lactic and glycolic acids. For this purpose, tin-containing alumina doped with СeO2, MoO3 and CuO oxides were synthesized by impregnation method. Textural and structural parameters of obtained МeO‑SnO2/Al2O3 mixed oxides were estimated from the results of low-temperature adsorption-desorption of nitrogen and X-ray diffraction. The formation of morphology ceria close to octahedra for CeО2‑SnO2/Al2O3 sample is confirmed by the X-ray phase analysis data and SEM microphotographs. The UV spectroscopy data indicates the nanosize of tin dioxide particles on the γ‑Al2O3 surface. According to the titration results, CeО2‑SnO2/Al2O3 is acid mixed oxide with H0 ≤ –3.0. The catalytic conversion of xylose solution in methanol was carried out in rotated autoclaves and in a flow stainless steel reactor with a fixed bed of catalyst. The products of the target reaction C5H10O5+2CH3OH+1/2O2 = C4H8O3+C3H6O3+2H2O were analyzed by 13C NMR. It was found that a complete conversion of 4 % xylose solution in a 70 % aqueous methanol solution occurs with the formation of methyl lactate (42 %) and methyl glycolate (24 %) on the developed CeO2-SnO2/Al2O3 catalyst loading of 3.5 mmol C5H10O5/gcat/h at 190 °C/3.0 MPa in air flow. The path of the reaction is proposed, namely: the IVSn4+ ions in           CeO2-SnO2/Al2O3 catalyst as Lewis acid sites promote retro-aldol xylose condensation and further Cannizzaro rearrangement of intermediate methyl pyruval hemiacetal into methyl lactate. And CeO2 provides selective oxidation of glycol aldehyde formed as a result of aldol decondensation of xylose to methyl glycolate. [ABSTRACT FROM AUTHOR]

Polylactic acid (PLA), as a biodegradable plastic, is considered a potential alternative to alleviate the environmental problems caused by the accumulation of petroleum-based plastic wastes. However, PLA is relatively expensive and naturally degrades very slowly. Therefore, compared to disposal, recycling PLA is more conducive to sustainable development. In this study, a novel immobilized deep eutectic solvent (DES) ChCl–2ZnCl2@ZIF-8 was developed and used for the methanolysis of PLA to produce a valuable product methyl lactate (ML). The synthesized heterogeneous catalyst exhibits excellent thermal and chemical stability, as well as excellent catalytic performance. For example, the reaction temperature significantly decreased, the dosage of the catalyst decreased, and the PLA conversion and the ML yield were both improved, reaching 98.2% and 96.3%. After the reaction, the catalyst can be recovered through simple filtration, and reused for five times with negligible loss of catalytic activity. The catalyst was characterized by FT-IR, SEM, BET, TGA and XRD. Based on the experimental results, a possible reaction mechanism of PLA methanolysis was proposed. In addition, the kinetics of the PLA methanolysis catalyzed by ChCl–2ZnCl2@ZIF-8 was examined and the activation energy was obtained. This work mainly provided a way of recovering catalysts and promoted the development of PLA methanolysis into ML. [ABSTRACT FROM AUTHOR]

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Biomass is a renewable alternative to fossil fuels and a valuable source of chemicals. In this study, a facile and efficient method was established to improve the selectivity of methyl lactate (MLA) for the homogeneous Lewis acid catalyzed chemical conversion of glucose and methanol. The effects of catalyst dosage, reaction temperature, and reaction time were systematically investigated, with an emphasis on the variation trends of MLA and other by-products. Through process optimization, the best catalyst molar ratio was 0.075 to 0.1, the reaction temperature was 170 to 180 °C, and the reaction time was 3 h. Under these conditions, the conversion of glucose in methanol exceeded 98%, and the yield of MLA was greater than 40%.

Two multifunctional catalytic systems comprising Sn-based/doped crystalline zeolite Beta were synthesized, and they were employed as heterogeneous catalysts in the selective conversion of glycerol to methyl lactate. The first catalytic system, named Au-Pd-Sn-deAl-7.2-Beta-DP, was created through the post-synthesis dealumination of the parent zeolite Beta (Si/Al = 10) using 7.2 M HNO3. Subsequently, it was grafted with 27 mmol of SnCl4, resulting in Sn-deAl-7.2-Beta. Following this, Au and Pd nanoparticles were supported on this catalyst using the deposition–precipitation (DP) method. The second catalytic system was a physical mixture of Au and Pd nanoparticles supported on functionalized carbon nanotubes (Au-Pd-F-CNTs) and Sn-containing zeolite Beta (Sn-deAl-7.2-Beta). Both catalytic systems were employed in glycerol partial oxidation to methyl lactate under the following conditions: 140 °C for 4.5 h under an air pressure of 30 bar. The Au-Pd-Sn-deAl-7.2-Beta-DP catalytic system demonstrated 34% conversion of glycerol with a 76% selectivity for methyl lactate. In contrast, the physical mixture of Au-Pd-F-CNTs and Sn-deAl-7.2-Beta exhibited higher activity, achieving 58% glycerol conversion and a nearly identical selectivity for methyl lactate (77%). The catalytic results and catalyst structure were further analyzed using various characterization techniques, such as X-ray diffraction (XRD), N2 physisorption, scanning electron microscopy (SEM), X-ray fluorescence (XRF), transmission electron microscopy (TEM), UV-vis spectroscopy, and pyridine Fourier transform infrared (FTIR). These analyses emphasized the significance of adjusting the quantity of active sites, particle size, and active sites proximity under the chosen reaction conditions. [ABSTRACT FROM AUTHOR]

The conversion of dihydroxyacetone solution in methanol to methyl lactate has been studied in flow regime using xSnO2/Al2O3-supported catalysts that have been characterized by XRD, low-temperature nitrogen (ad)desorption analysis, and UV-Vis spectroscopy. It is found that Lewis and Brønsted acid sites of the surface of SnO2-containing catalysts play a crucial role in the selective conversion of dihydroxyacetone to methyl lactate. The formation of methyl lactate with a selectivity of 90% is achieved on 5%SnO2/Al2O3 catalyst at 160°C, 1.0 MPa, and under feed rate of 4 mmol C3H6O3/(gcat·h). [ABSTRACT FROM AUTHOR]

Via hydrothermal synthesis of Sn‐Al gels, mild dealumination and ion exchange, a bimetallic Sn‐Ni‐Beta catalyst was prepared which can convert glucose to methyl lactate (MLA) and methyl vinyl glycolate (MVG) in methanol at yields of 71.2 % and 10.2 %, respectively. Results from solid‐state magic‐angle spinning nuclear magnetic resonance, X‐ray photoelectron spectroscopy, transmission electron microscopy, spectroscopic analysis, probe‐temperature‐programmed desorption, and density functional theory calculations conclusively reveal that the openness of the Sn sites, such as by the formation of [(SiO)3−Sn−OH] entities, is governed by an adjacent metal cation such as Ni2+, Co2+, and Mn2+. This relies on the low structure‐defective pore channel, provided by the current synthesis scheme, and the specific silica hydroxyl anchor point is associated with the incorporation of Sn for additional and precise metal ion localization. The presence of metal cations significantly improved the catalytic performance of Sn‐Ni‐Beta for glucose isomerization and conversion to MLA of sugar compared with Sn‐Beta. [ABSTRACT FROM AUTHOR]

The catalytic behaviors of various tin compounds for the conversion of 1,3-dihydroxyacetone (DHA) to methyl lactate (ML) in methanol, as well as the reaction process, were briefly investigated in a batch reactor. The results indicated that metal cations with strong Lewis acidity, in particular Sn2+ and Sn4+, catalyzed efficiently the conversion of DHA to ML. The performance of tin cation was closely related to its counterpart anions, with the halide anions (Cl- and Br-) acting as promoters. Besides, high temperature favored the yield of methyl lactate when SnCl2 served as a catalyst, yielding the DHA conversion and ML selectivity of 98.2% and of 96.0% respectively at 100℃ Moreover, the evolution of reaction products against time suggested that the conversion of DHA to ML proceeded through a combination of consecutive and parallel reaction steps. Pyruvic aldehyde hemiacetal was the detectable reaction intermediate, whereas ML proved to be final products. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two new reaction pathways are disclosed for methyl lactate synthesis from cellulose. • Water plays important role in tailoring the hydrolysis of SnCl 2 to Sn(II) species. • SnCl x (OH) 2- x are efficient for isomerization and retro -aldol condensation reactions. • As high as 91.5% of total selectivity towards desired products was achieved. Catalytic conversion of cellulose into lactic acid (LA) is paramount for the emerging biomass-based chemical industry. With emphasis on the reaction mechanism, the catalytic cellulose conversion to methyl lactate (ML) was systematically investigated in water-containing methanol solution. The role that water plays and catalytic mechanism of the acidic and basic sites were analyzed and discussed. It was found that water played an important role in modulating hydrolysis of SnCl 2 to release H+ protons and basic SnCl x (OH) 2-x species. These basic species are very efficient for the isomerization and [3+3] retro aldol condensation in terminal glucose units of cellulose chain, while H+ protons facilitate the ring-opening of the ends of cellulose chains to trioses rather than hydrolysis of the glucoside bonds to form glucose. Based on advanced characterization techniques including ESI-MS, GPC, FT-IR, XRD, XPS and CP-MAS 13C NMR as well as DFT calculations, two new reaction pathways were disclosed for the first time, which are distinct from the well-known traditional pathway that goes through the formation of glucose. Owing to the exclusion of the formation of glucose during the cellulose conversion, the selectivity towards ML can be greatly enhanced. Under optimal conditions, the total selectivity could reach to 91.5 % with a ML and LA yield of 66.3 %. These findings provide new insights into the catalytic conversion of cellulose into value-added chemicals and help explore effective catalysts. [ABSTRACT FROM AUTHOR]

Two multifunctional catalytic systems comprising Sn-based/doped crystalline zeolite Beta were synthesized, and they were employed as heterogeneous catalysts in the selective conversion of glycerol to methyl lactate. The first catalytic system, named Au-Pd-Sn-deAl-7.2-Beta-DP, was created through the post-synthesis dealumination of the parent zeolite Beta (Si/Al = 10) using 7.2 M HNO3. Subsequently, it was grafted with 27 mmol of SnCl4, resulting in Sn-deAl-7.2-Beta. Following this, Au and Pd nanoparticles were supported on this catalyst using the deposition–precipitation (DP) method. The second catalytic system was a physical mixture of Au and Pd nanoparticles supported on functionalized carbon nanotubes (Au-Pd-F-CNTs) and Sn-containing zeolite Beta (Sn-deAl-7.2-Beta). Both catalytic systems were employed in glycerol partial oxidation to methyl lactate under the following conditions: 140 °C for 4.5 h under an air pressure of 30 bar. The Au-Pd-Sn-deAl-7.2-Beta-DP catalytic system demonstrated 34% conversion of glycerol with a 76% selectivity for methyl lactate. In contrast, the physical mixture of Au-Pd-F-CNTs and Sn-deAl-7.2-Beta exhibited higher activity, achieving 58% glycerol conversion and a nearly identical selectivity for methyl lactate (77%). The catalytic results and catalyst structure were further analyzed using various characterization techniques, such as X-ray diffraction (XRD), N2 physisorption, scanning electron microscopy (SEM), X-ray fluorescence (XRF), transmission electron microscopy (TEM), UV-vis spectroscopy, and pyridine Fourier transform infrared (FTIR). These analyses emphasized the significance of adjusting the quantity of active sites, particle size, and active sites proximity under the chosen reaction conditions.

The efficient preparation of catalyst is an important topic for its industrial application. The Sn‐containing zeolite is one kind of important catalysts for many catalytic conversions of oxygenated chemicals. In this work, an efficient strategy for preparation of Sn‐MFI zeolite was developed, of which space‐time yield can reach 62.58 kg/m3⋅h, which is 120 times higher than that of typical hydrothermal route (0.53 kg/m3⋅h). Combining XRD, TEM, XPS, FT‐IR, 29Si NMR and other characterization methods, the framework tin sites were confirmed, and key role of ethylenediamine (EDA) for formation of which was revealed. Additionally, the framework tin sites content and catalytic activity of the Sn‐MFI prepared by this strategy is comparable to that of Sn‐MFI‐hy prepared by typical route in the conversion of dihydroxypropanone (DHA) to methyl lactate (ML), which gives ML yield of 80.64 % under optimized conditions. The proposed methodology can be extended to other types of Sn‐containing zeolite, which will certainly promote its industrial application. [ABSTRACT FROM AUTHOR]

Sn‐Beta zeolites were successfully synthesized through a quasi‐solid‐phase method by grinding the raw materials and then crystallizing in solid state. The method employed small amount of tetraethyl ammonium hydroxide (TEAOH) and no additional solvent, except for the water contained in template solution. The synthesis conditions including amount of TEAOH and water, and crystallization time were explored. Under optimized conditions, the obtained sample showed high crystallinity and capped square bipyramidal crystals. The diffuse reflectance ultraviolet‐visible spectra and Fourier transform infrared spectra of CD3CN and pyridine adsorption were used to characterize the state of Sn and acidity in Sn‐Beta sample. Sn4+ ions were introduced into the framework which generated strong Lewis acid sites. The sample synthesized by quasi‐solid‐phase method gave 38.5 % methyl lactate (MLA) yield for the conversion of glucose to MLA, which is comparable to that of Sn‐Beta prepared with conventional hydrothermal method (39.4 %). [ABSTRACT FROM AUTHOR]

Methyl lactate (MLA) is a versatile high value platform chemical prepared from biomass carbohydrates, with widely application in the pharmaceutical, food, pesticide, and cosmetics. The current study presented a one-pot catalytic conversion of sugars to MLA over poly (ionic liquid)s functionalized Sn/Beta zeolites under mild conditions. The Sn/Beta zeolites were prepared by an impregnation method, followed by modification with poly (vinyl imidazole) ([PVIM]) via an in-situ free radical polymerization method. Dosages of polymer and Sn, calcination temperature, reaction temperature, catalyst amount, substrate concentration, and reaction times were optimized. Results showed that an MLA yield of 61.4 % was obtained over 3[PVIM]-Sn/Beta with complete conversion of fructose at 140 °C for 8 h. The physicochemical properties were characterized by XRD, BET, FTIR, CO-DRIFTS, NH 3 -TPD and pyridine-FTIR analysis, indicating the coexistence of Lewis and Brønsted acid sites. Finally, a possible reaction mechanism was proposed that the weak Lewis acidity of imidazole rings of [PVIM] effectively regulated the local microenvironment of active sites, thus promoting the interaction of the active sites with electronegative oxygens of sugars. This study can provide as a reference for the development of solid acid catalysts for the catalytic conversion of biomass to platform chemicals. [Display omitted] • Bifunctional Sn/Beta prepared by impregnation/in-situ radical polymerization method. • Effective regulation of local microenvironment of active sites by [PVIM]. • A promising MLA yield of 61.4 % from fructose was obtained at 140 °C for 8 h. • Facile catalyst recovery and recycling. [ABSTRACT FROM AUTHOR]

Methyl lactate (MLA), a versatile biomass platform, was typically produced from the catalytic conversion of high-priced fructose. High fructose corn syrup (HFCS) is a mixture of glucose, fructose, water, etc., which is viewed as an economical substitute for fructose to produce MLA due to the much lower cost of separation and drying processes. However, the transformation of HFCS to MLA is still a challenge due to its complex components and the presence of water. In this work, the catalytic conversion of HFCS to MLA over CoO@silicalite-1 catalyst synthesized via a straightforward post citric acid treatment approach was reported. The maximum MLA yield reached 43.8% at 180 °C for 18 h after optimizing the reaction conditions and Co loading. Interestingly, adding extra 3% water could further increase the MLA yield, implying that our CoO@silicalite-1 catalyst is also capable for upgrading wet HFCS. As a result, the costly drying process of wet HFCS can be avoided. Moreover, the activity of CoO@silicalite-1 catalyst can be regenerated for at least four cycles via facile calcination in air. This study, therefore, will provide a new opportunity to not only solve the HFCS-overproduction issues but also produce value-added MLA. [ABSTRACT FROM AUTHOR]

A yttrium modified ZSM‐5 zeolite (Y‐ZSM‐5) for catalytic production of methyl lactate (MLA) has been prepared through the ion exchange of commercially available H‐ZSM‐5 with yttrium chloride (YCl3) and subsequent calcination procedures. The successful preparation of Y‐ZSM‐5 was characterized by X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), inductively coupled plasma atomic emission spectrometry (ICP), Fourier transform infrared spectroscopy (FT‐IR), scanning electron microscope (SEM), and nitrogen adsorption‐desorption measurement (BET method). The acid property of Y‐ZSM‐5 was investigated through NH3‐temperature programmed desorption (NH3‐TPD), and pyridine adsorption Fourier‐transform infrared spectroscopy (Py‐IR), demonstrating the introduction of Y3+ species could enhance the acid sites of zeolite. The as‐prepared Y‐ZSM‐5 is an efficient catalyst for the catalytic conversion of fructose‐based carbohydrates into methyl lactate (MLA). Under the optimum conditions, 61.3 % of MLA yield can be afforded from fructose. Furthermore, sucrose and inulin could give 39.6 % and 45.6 % of MLA yield, respectively. Meanwhile, the Y‐ZSM‐5 is structurally stable and reusable, after being recycled 5 times, the catalyst showed no appreciable loss of activity. [ABSTRACT FROM AUTHOR]

Bimetallic modified Fe–Sn/Beta was synthesized and examined as a solid acid catalyst for the transformation of glucose into methyl lactate in methanol. The catalysts were characterized by a combined characterization techniques i.e. X-ray fluorescence spectroscopy, N2 physisorption, powder X-ray diffraction, X-ray photoelectron spectroscopy, NH3 temperature-programmed desorption, and pyridine adsorption Fourier transform infrared spectroscopy. A high yield of methyl lactate of 67% was achieved upon conversion of 0.3 g glucose in 24 g methanol over 0.15 g catalyst at 220 ℃ under 2 MPa N2 for 6 h. The recyclability of the catalyst was also investigated, and the conversion of glucose remained constant; conversely, the yield of methyl lactate decreased slightly in five catalytic runs. The excellent catalytic performance of Fe–Sn/Beta was attributed to the presence of large amounts of Lewis acid sites. Besides, the rich mesoporosity in Fe–Sn/Beta improved mass transfer rates in the conversion of glucose to alkyl lactates. [ABSTRACT FROM AUTHOR]

BACKGROUND Methyl lactate is widely applied in the chemical, food, cosmetics and pharmaceutical industries. The conversion of carbohydrates over heterogeneous catalysts to methyl lactate is a promising environmentally benign process. RESULTS: Hierarchical Sn‐Beta zeolite (Sn‐Beta) and corresponding bimetal‐doped Beta zeolites (M‐Sn‐Beta; M = Zn, In, La, Ga, Ni) were prepared via a novel modified hydrothermal synthesis method to convert carbohydrates into methyl lactate. The introduction of Zn into Sn‐Beta considerably improved the yield of methyl lactate from glucose, while for the catalysts containing In, La, Ga and Ni, such improvements were not observed. CONCLUSIONS: A methyl lactate yield reaching up to 66.7% was obtained over Zn‐Sn‐Beta at 220 °C for 6 h. The enhanced catalytic performance was attributed to high Lewis acid density and strength, together with synergistic effects between framework Sn4+ and Zn2+ ions of Zn‐Sn‐Beta. Additionally, Zn‐Sn‐Beta demonstrated fructose and sucrose conversion into methyl lactate with yields of 68.4% and 70.0%, respectively. The Zn‐Sn‐Beta catalyst could be re‐used at least five times with only a slight loss of methyl lactate yield. © 2021 Society of Chemical Industry (SCI). [ABSTRACT FROM AUTHOR]

Alkyl lactates represent such green added-value chemicals that commonly used as biodegradable green solvents, detergents, pharmaceutical intermediates et al. Catalytic conversion of carbohydrates to methyl lactate (MLA) is a representative way for high-value utilization of biomass and the key lies in the development of highly efficient catalysts. In methanol, strong acid or alkaline catalysts are usually used under high temperature and high pressure, suffering from problems such as low selectivity, high cost or contamination of environment. This study aims to develop an acid-base bifunctional heterogeneous catalyst for the one-pot conversion of sugars to MLA under mild conditions. Sn/Mg composite oxides was synthesized by a coprecipitation method and further modified by poly (vinyl imidazole) ([PVIM]) to tune the hydrophilicity. Effect of polymer and Sn amount, calcination temperature, reaction temperature, catalyst dosage, and substrate concentration were investigated. The acid-base properties were characterized by NH 3 -TPD, pyridine-FTIR and CO 2 -TPD analysis. It was found that the presence of medium acid sites and medium base sites played an important role to the cascade reactions of carbohydrates to MLA. An optimum MLA yield of 55.4% was achieved over 10[PVIM]-5Sn/MgO (0.05 g) with complete conversion of glucose (28 mM) at 140 ℃, 2 MPa N 2 for 10 h. The reaction conditions are mild and no strong acid or strong base catalyst is required. Furthermore, a possible reaction mechanism was proposed that the introduction of [PVIM] effectively regulated the local microenvironment of active sites and the acid base synergism greatly promoted the retro-aldol condensation, dehydration and hydrogen transfer reactions during the conversion of glucose to MLA. [Display omitted] • Acid-base bifunctional Sn/MgO catalyst for the one-pot conversion of sugars to MLA. • Poly (vinyl imidazole) efficiently tuned the local microenvironment of active sites. • A promising MLA yield of 55.4% from glucose was obtained at 140 °C for 10 h. • Medium acid-base sites greatly promoted the cascade reactions of glucose to MLA. [ABSTRACT FROM AUTHOR]

• A facile and commercially available catalytic system. • Ultrafast alcoholysis of PLA to methyl lactate at room temperature. • Large-scale depolymerization of PLA and selective depolymerization of mixed plastics. • A catalytic system with excellent recyclability. The depolymerization of waste plastics into high-value products is a promising solution to address the plastic crisis. Among this field, catalytic activity and selectivity of depolymerization catalyst are of great concerns. Accordingly, in this work, a simple catalytic system was explored in detail to achieve the fast and selective chemical recycling of PLA into methyl lactate. Using commercially available M[bis(trimethylsilyl)amide] (MHMDS, M = Li, Na, K) as catalysts, the depolymerization of PLA was completed within a few minutes at room temperature. The selectivity and optical purity of the depolymerized product methyl lactate are greater than 99 %. The effect of conditions such as metal center, catalyst form, and solvent on depolymerization was investigated. Moreover, the gram-grade depolymerization, selective depolymerization of blended or mixed PLA plastic, and the recyclability of catalyst were further explored. This work accomplishes the path of highly selective and active depolymerization of PLA under mild conditions, thereby promoting sustainable development of PLA. [ABSTRACT FROM AUTHOR]

[Display omitted] The developed In/γ-Al 2 O 3 catalyst exhibited outstanding efficiency for the production of methyl lactate (MLA) directly from renewable sugars, due to the significant increase of mid-strong acid and base sites, affording MLA yields as high as 49.0 % and 54.2 % from glucose and fructose, respectively. • 12-In/γ-Al 2 O 3 exhibited the best efficiency for methyl lactate production. • In doping facilitated the selective cleavage of C3-C4 bond of C6 sugar. • Water and K 2 CO 3 addition further promoted the yield of methyl lactate. • 49.0 % and 54.2 % yields were obtained from glucose and fructose, respectively. The huge demand of lactic acid in widespread applications has significantly impelled the development of cost-effective strategy for the production of lactic acid, in particular its derivative (methyl lactate, MLA) due to the simpler separation and purification process. Herein, in this work, we developed a series of robust but simple In/γ-Al 2 O 3 catalysts with different In loadings. The results indicated that In doping obviously increased the amount of mid-strong acid on the catalyst, which significantly facilitated the selective cleavage of C3-C4 bond in C6 sugar (rate-controlling step), as well as the next esterification reaction. 12-In/γ-Al 2 O 3 catalyst, with the most mid-strong acid sites, exhibited the best catalytic activity for MLA production from renewable sugars in methanol solvent. The addition of only a small amount of water could accelerate sugar dissolution in methanol solvent, and alkali (K 2 CO 3) addition further promoted C3-C4 cleavage, thus yielding more C3 intermediates. When dihydroxyacetone and pyruvaldehyde intermediates were employed as feedstock, as high as 86.0 % and 98.0 % yields of MLA could be obtained, respectively. Even in the case of glucose and fructose as feedstock, MLA yields were up to 49.0 % and 54.2 %, respectively, under the optimized conditions. This work might provide a potential approach for the synthesis of lactic acid and its derivatives with low production cost. [ABSTRACT FROM AUTHOR]

Methyl lactate (MLA), a versatile biomass platform, was typically produced from the catalytic conversion of high-priced fructose. High fructose corn syrup (HFCS) is a mixture of glucose, fructose, water, etc., which is viewed as an economical substitute for fructose to produce MLA due to the much lower cost of separation and drying processes. However, the transformation of HFCS to MLA is still a challenge due to its complex components and the presence of water. In this work, the catalytic conversion of HFCS to MLA over CoO@silicalite-1 catalyst synthesized via a straightforward post citric acid treatment approach was reported. The maximum MLA yield reached 43.8% at 180 °C for 18 h after optimizing the reaction conditions and Co loading. Interestingly, adding extra 3% water could further increase the MLA yield, implying that our CoO@silicalite-1 catalyst is also capable for upgrading wet HFCS. As a result, the costly drying process of wet HFCS can be avoided. Moreover, the activity of CoO@silicalite-1 catalyst can be regenerated for at least four cycles via facile calcination in air. This study, therefore, will provide a new opportunity to not only solve the HFCS-overproduction issues but also produce value-added MLA.

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.

• Brönsted acid attribute to the induction of hydroxyl groups by framework Sn • DHA dehydration by Brönsted acid is the rate-determining step. • HA isomerization by Lewis acid boosts the selectivity of ML. • Isotopic labeling technology verifies the proposed mechanism. To investigate the effects of the acid characteristic of Sn-MFI zeolite on catalytic performance in the transformation of dihydroxyacetone to methyl lactate, multiple characterization and experimental methods were employed. Firstly, the transformation between Lewis and Brönsted acid sites was initially confirmed by 31P-TMP NMR method, owing to the introduction of CH 3 OH by framework Sn species to donate protons. It is found that Lewis acid sites are cooperative with Brönsted acid sites to boost the primary reactions of dihydroxyacetone (DHA) to methyl lactate (ML). Yet, too high ratio of Brönsted acid sites to Lewis acid sites favors the generation of side product pyruvic aldehyde dimethyl acetal (PADA). That is because Brönsted acid sites majorly catalyze the dehydration of DHA, the addition of pyruvaldehyde (PA) with methanol and the addition of hemiacetal (HA) with methanol to PADA, whereas Lewis acidic framework Sn sites are responsible for the isomerization of HA to ML, which can be further verified by the isotopic labeling experiments. Therefore, this study provides a definite and systematical insight on the impacts of acid property on product selectivity. [ABSTRACT FROM AUTHOR]

One-pot conversion of biomass-based carbohydrates to methyl lactate (MLA), a versatile platform chemical for the production of food additives as well as the starting material of pharmaceutical industry, is an attractive green process. In this study, the Nb/HUSY catalysts with highly catalytic performance are successfully synthesized and used for the production of MLA from fructose. Remarkably, when using 2%Nb/HUSY as catalyst, the highest MLA yield of 56.1% is obtained with complete conversion of fructose under optimal conditions (140 °C for 6 h). The introduction of niobium into HUSY enhances the Lewis acid properties, which facilitates the stepwise process, involving the retro-aldol condensation and dehydration reactions. The as-prepared catalysts have shown promising potential for conversion of fructose to MLA and effectively inhibited the formation of by-products. More importantly, the catalyst exhibits superior stability and could be reused for at least four cycles. Image 1 • A controllable transformation of fructose into green methyl lactate is demonstrated. • The combination of strong Lewis and weak Brønsted acid enhanced catalytic activity. • The Lewis/Brønsted ratios of the Nb/HUSY catalysts can be easily tuned. • The as-prepared catalysts afford superior catalytic performance. [ABSTRACT FROM AUTHOR]

Recent developments in sugar transformations to methyl lactate and lactic acid are critically summarized. The highest yield of methyl lactate from glucose obtained over Sn(salen)/octylmethyl imidazolium bromide catalyst was 68 % at 160 °C whereas the highest yield of lactic acid of 58 % was achieved over hierarchical Lewis acidic Sn‐Beta catalysts at 200 °C under inert atmosphere. In addition to the desired products also humins are formed in water whereas in methanol alkyl glucosides‐ and ‐fructosides as well as acetals were generated, especially in the presence of Brønsted‐acidic sites. The main challenges limiting the industrial feasibility of these reactions are incomplete liquid phase mass balance closure, complicated product analysis and a lack of kinetic data. In addition to reporting optimized reaction conditions and catalyst properties also catalyst reuse and regeneration as well as kinetic modelling and continuous operation are summarized. [ABSTRACT FROM AUTHOR]

BACKGROUND: Fast pyrolysis of lignocellulosics has provided an abundant sugar source for production of value‐added chemicals, and levoglucosan is the most representative sugar in pyrolysis liquid (bio oil). This paper explored the potential for producing methyl lactate from levoglucosan by employing the mixed catalysts of zeolite tin beta (Sn‐Beta) and zeolite hydrogen beta (H‐Beta). RESULTS: Under the optimal conditions (at 200 °C and mixed catalysts with H‐Beta:Sn‐Beta ratio of 1:5), the yield of methyl lactate obtained from levoglucosan conversion was as high as 35%. And the yield was comparable to that of methyl lactate obtained from glucose conversion under the similar conditions (at 200 °C and pure Sn‐Beta). In order to investigate the reason, a contrasting experiment with glucose as substrate also was carried out with the mixed catalysts. The results indicated that during the levoglucosan conversion process, 'the methanolysis of levoglucosan' was likely to compete with 'the dehydration of glucose' for the Brønsted acid sites of H‐Beta. In addition, the catalytic functions of H‐Beta and Sn‐Beta, and the reaction pathway were deeply investigated through tracking and comparing the conversion of levoglucosan over mixed H‐Beta/Sn‐Beta and over pure Sn‐Beta catalysts, respectively. CONCLUSION: The appropriately lower ratio of H‐Beta:Sn‐Beta and relatively higher temperature were favorable for the reaction. H‐Beta containing Brønsted acid could remarkably accelerate the conversion of levoglucosan and methyl‐glucosides to glucose. Sn‐Beta containing Lewis acid mainly promoted the retro‐aldol condensation of glucose and formation of methyl lactate. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

• A low-cost and easily synthesized DESs ChCl-2ZnCl 2 was used to catalyze the methanolysis of PLA very fast and effectively under moderate conditions. • The reaction was carried out in absence of any other traditional acid or base catalyst. • The DES can be reused 5 times without obvious decrease in reaction results. • An environmentally friendly strategy was provided for methanolysis of PLA waste. • The reaction was a pseudo-first order kinetic one and activation energy was obtained. Methyl lactate (ML) is a green and biodegradable chemical product, which can be used as a solvent for cellulose, paints and dyes. Although several kinds of catalysts have been reported for the methanolysis of Polylactic acid (PLA) into ML, low catalytic activity and high cost and complicated operation are still problems. Renewable, environmentally friendly, and non-toxic choline chloride-based Deep eutectic solvents (DESs) are the newest alternatives to conventional catalysts for the methanolysis of PLA to obtain the valuable product ML. In this study, the methanolysis of PLA into ML using DESs composed of choline chloride (ChCl) and Zinc chloride (ZnCl 2) was investigated by experiments and calculations. Experimental results reveal that ChCl-2ZnCl 2 can catalyze the methanolysis of PLA to produce ML, more importantly, ML is easily obtained by vacuum distillation, and the catalyst can be reused for 5 times without significant loss of activity. Moreover, the possible reaction mechanism was derived from experimental data and density functional theory (DFT) calculations. And the kinetics of the methanolysis of PLA catalyzed by ChCl-2ZnCl 2 was studied and the activation energy was obtained. This work reveals that ChCl/ZnCl 2 DESs are conducive to the methanolysis of PLA to ML under moderate conditions, which can also provide strategies for other polymer degradation. [ABSTRACT FROM AUTHOR]

Bimetallic zeolite Beta in bead format and containing Al sites with Brønsted acid behavior and Sn, Zr or Hf sites with Lewis acid character, were prepared using a two-step synthetic route. First, zeolite Beta in the format of macroscopic beads (400 to 840 μm) with hierarchical porosity (micropores accessed through meso- and macropores in the range of 30 to 150 nm) were synthesized by hydrothermal crystallization in the presence of anion-exchange resin beads as hard template and further converted into their H-form. Next, the zeolite beads were partially dealuminated using different concentrations of HNO3 (i.e., 1.8 or 7.2 M), followed by grafting with one of the above-mentioned metals (Sn, Zr or Hf) to introduce Lewis acid sites. These bimetallic zeolites were tested as heterogeneous catalysts in the conversion of dihydroxyacetone (DHA) to methyl lactate (ML). The Sn-containing zeolite Beta beads treated by 1.8 M HNO3 and grafted with 27 mmol of SnCl4 (Sn-deAl-1.8-Beta-B) demonstrated the best catalytic activity among the prepared bimetallic zeolite beads, with 99% selectivity and 90% yield of ML after 6 h at 90 °C. This catalyst was also tested in combination with Au-Pd nanoparticles supported on functionalized carbon nanotubes (CNTs) as multifunctional catalytic system for the conversion of glycerol to ML, achieving 29% conversion of glycerol and 67% selectivity towards ML after 4.5 h at 140 °C under 30 bar air. The catalytic results were rationalized by means of a thorough characterization of the zeolitic beads with a combination of techniques (XRD, N2-physisorption, SEM, XRF, TEM, UV-vis spectroscopy and pyridine-FT-IR).

• Glycerol was converted to methyl lactate directly over binary Au/CuO and Sn-Beta catalyst. • 86% glycerol conversion and 60% methyl lactate yield can be obtained at 90 °C. • CuO precursors have great influence on the oxidative catalytic activity of Au/CuO. • Oxygen mobility of CuO prepared from copper acetate is the highest. • Au particles on CuO from copper acetate are small (2–4 nm) and uniform. Utilization of glycerol is important for the sustainable development of biodiesel industry. In this study, green conversion of glycerol to methyl lactate was realized over Au/CuO and Sn-Beta binary catalyst at low temperature in base-free methanol, 86% glycerol conversion and 60% methyl lactate yield can be obtained at 90 °C. Precursors for preparation of CuO have significant influence on the catalytic oxidative activity of Au/CuO. Oxygen mobility of CuO prepared from copper acetate (CuO-CA) is the highest compared to CuO materials prepared from copper nitrate (CuO-CN) and commercial CuO (CuO-Commercial). Meanwhile, dispersion of Au particles is significantly affected by the precursor for synthesis of CuO. Au particles on CuO-CA are small (2–4 nm) and uniform. Accordingly, Au/CuO-CA shows the best catalytic activity for the oxidation of glycerol. Synergism of oxidative active sites on Au/CuO-CA and Lewis acid sites on Sn-Beta facilitates the production of methyl lactate from glycerol. Meanwhile, the catalysts are recyclable and can be reused easily without any treatment. [ABSTRACT FROM AUTHOR]

Sn-beta zeolites are among the most promising catalysts for the conversion of biomasses due to their high Lewis acidity, which allows coordination to functionalized molecules and promotes cleavage and rearrangement reactions. For applications in biorefining zeolite porosity would ideally be optimized to avoid diffusional limitations, which otherwise may decrease reaction rates and restrict the conversion of bulky substrates. The synthesis of mesoporous zeolites can help alleviating limitations and is a central topic in heterogeneous catalysis, with many synthetic procedures for mesoporous zeolites proposed over the last decades. Here, we explore different syntheses routes to prepare Lewis acidic Sn-containing zeolites, and the main features of the prepared mesoporous materials are characterized. We investigate the correlation between different types of porosity and the activity for the conversion of sugars into methyl lactate. The monomer glucose, the dimer sucrose and the oligomer inulin are applied as model substrates for the reaction in order to probe the accessibility of molecules with different sizes to active sites in zeolites with different pore systems. [ABSTRACT FROM AUTHOR]

BACKGROUND Glycerol is a versatile platform compound to produce valuable chemicals. One‐pot direct conversion of glycerol into methyl lactate with methanol as solvent is very attractive, because it can reduce intermediate steps and avoid the separation of glycerol/methanol mixtures. RESULTS: A series of tin (Sn)‐exchanged montmorillonite(M)‐supported Au catalysts were prepared by a combination of ion exchange and colloidal deposition methods, and designed as bifunctional catalysts containing gold (Au) and solid acid. These catalysts were employed for one‐pot conversion of glycerol to methyl lactate in methanol. The Au/Sn(20)‐Mt catalyst gave a high yield of methyl lactate of 54% upon conversion of 0.25 mol L–1 glycerol methanol solution over 0.07 g catalyst at 210 °C under 3 MPa air for 5 h. The good performance of Au/Sn(20)‐Mt was ascribed to the coexistence of small Au particle and abundance of acid sites. The glycerol conversion remained almost unchanged in the five recycled runs, whereas the methyl lactate yield decreased after the first run but kept stably in the later four catalytic runs. CONCLUSIONS: Among the series of Sn‐exchanged Mt‐supported Au catalysts, Au/Sn(20)‐Mt showed the highest glycerol conversion and methyl lactate yield. Containing both small Au particles and having an abundance of acid sites contributed to the excellent catalytic activity of Au/Sn(20)‐Mt. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

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Abstract Catalytic mechanism of NiO on the conversion fructose to methyl lactate (MLA) has been evaluated in this work. NiOs were calcined at various temperatures. NiOOH was detected on the surface of NiO. The amount of NiOOH as well as the product yield of MLA decreased with an increase in the calcination temperature of NiO. We have demonstrated that NiOOH could facilitate the catalytic conversion of fructose to MLA. This work provides some new insights into the NiO catalytic production of MLA. These results will guide the preparation of nickel based solid catalysts for the MLA production. Graphical abstract Unlabelled Image Highlights • Catalytic mechanism of NiO for the production of methyl lactate has been evaluated. • NiOOH was detected on the surface of NiO. • Concentration of NiOOH decreased with the increase of calcination temperature. • NiOOH on the surface of NiO could facilitate the production of methyl lactate. [ABSTRACT FROM AUTHOR]

Sn-containing MFI zeolites with controllable Al contents were successfully synthesized with the utilization of the EDTA-Sn complex as tin source and citrate as buffer solution for the first time. The elaborately strategy achieves a right release of Sn 4+ ions rate to combine with the silicon tetrahedron species in the synthesis process which could make the heteroatom tin warmly incorporate into the zeolite frameworks. The structural information about the Sn-containing MFI zeolites was confirmed by XRD, FTIR, and solid-state NMR spectroscopy. Characterization results of HRTEM, FTIR, XPS, and UV-vis spectroscopy illustrated that most Sn species exist as isolated tetrahedral Sn(IV) in the as-prepared zeolites. The creation of Lewis acid sites in Sn-MFI and Sn-Al-MFI zeolites, and Brønsted acid sites in Sn-Al-MFI zeolites were determined by FTIR spectroscopy of pyridine adsorption and 1 H and 31 P MAS NMR spectroscopy after ammonia and trimethylphosphine oxide (TMPO) adsorption. Both the Sn-MFI and Sn-Al-MFI zeolite catalysts exhibit a remarkable catalytic performance in the conversion of dihydroxyacetone (DHA) to methyl lactate (ML), while the bifunctional Sn-Al-MFI catalyst exhibits a significant combination effect, and a remarkable active site-based turnover frequency with a high methyl lactate productivity can be achieved. [ABSTRACT FROM AUTHOR]

Abstract: Considerable progress has been made recently in the catalytic conversion of renewable biomass resources to methyl lactate (MLA). However, conceiving eco‐friendly and effective catalytic systems for the production of MLA from biomass carbohydrates remains a key challenge. Herein, we report a multifunctional catalyst Sn(salen)/IL, consisting of a Sn(salen) complex and an imidazolium‐based ionic liquid (IL), which acts via an intramolecular synergistic effect to convert carbohydrates to MLA in methanol. The versatile properties of the resultant catalyst were revealed to be responsible for the conversion of fructose to MLA and the efficient suppression of undesired side reactions. This catalyst displayed outstanding catalytic activity, high selectivity, and excellent recyclability, giving an MLA yield of up to 68.9 % at 160 °C after 2 h. The results of this study will contribute to new approaches for designing synergistic catalysts for producing liquid fuels and chemicals from biomass resources. [ABSTRACT FROM AUTHOR]

Metal organic frameworks (MOFs) are promising heterogeneous catalysts for biomass conversion to useful chemicals. In this work, four M-MOF-74s (Co, Ni, Mg, Zn) were synthesized at room temperature. Among these, Mg-MOF-74 exhibited the best catalytic activity for conversion of sugars to methyl lactate. A final product yield of methyl lactate from glucose of 35% was achieved with complete conversion of glucose at optimal reaction conditions. Catalytic performance of conversion of five sugars to methyl lactate over Mg-MOF-74 was studied, a product yield of 47% were obtained from sucrose. Mg-MOF-74 catalyst has shown to be reusable for at least three cycles. [ABSTRACT FROM AUTHOR]