Selective lactic acid synthesis via ethylene glycol electrooxidation in borate buffer

Efficient and selective oxidation of ethylene glycol is challenging due to uncontrollable C-C bond cleavage. We propose an electrochemical strategy for the selective electrooxidation of ethylene glycol to sythesise lactic acid on a Ni-based electrocatalyst by controlling the pH value of the electrolyte solution.

Homogeneous and Heterogeneous Catalysis of Glucose to Lactic Acid and Lactates: A Review

The current societal demand to replace polymers derived from petroleum with sustainable bioplastics such as polylactic acid (PLA) has motivated industry to commercialize ever-larger facilities for biobased monomers like lactic acid. Even though most of the lactic acid is produced by fermentation, long reaction times and high capital costs compromise the economics and thus limit the appeal of biotechnological processes. Catalytic conversion of hexose from biomass is a burgeoning alternative to fermentation. Here we identify catalysts to convert glucose to lactic acid, along with their proposed mechanisms. High Lewis acidity makes erbium salts among the most active homogeneous catalysts, while solvent coordination with the metal species polarize the substrate, increasing the catalytic activity. For heterogeneous catalysts, Sn-containing bimetallic systems combine the high Lewis acidity of Sn while moderating it with another metal, thus decreasing byproducts. Hierarchical bimetallic Sn-Beta zeolites combine a high number of open sites catalyzing glucose isomerization in the mesoporous regions and the confinement effect assisting fructose retro-aldol in microporous regions, yielding up to 67% lactic acid from glucose. Loss of activity is still an issue for heterogeneous catalysts, mostly due to solvent adsorption on the active sites, coke formation, and metal leaching, which impedes its large scale adoption.

Valorizing natural-abundant glucose to lactic acid using a MOF-808 catalyst under green hydrothermal conditions

Highly robust Zr-based MOF-808, featuring Lewis acid Zr sites and coordinate hydroxide ions upon the removal of the monocarboxylate capping reagent, emerges as an efficient catalyst for the hydrothermal conversion of glucose into lactic acid. A remarkable 99% glucose conversion with an impressive 76.6% yield of lactic acid can be achieved. The large pore window of MOF-808 facilitates the diffusion of glucose to the active sites within the framework. The single-site attribute of the catalytic center enables a high selectivity of lactic acid over the competitive product, 5-(hydroxymethyl)furfural, under hydrothermal reaction conditions.

Theoretical study of fructose adsorption and conversion to trioses on metal-organic frameworks

The conversion of chemically modified biomass into more valuable chemicals has recently gained significant attention from industry. In this study, we investigate the adsorption of fructose and its conversion into two trioses, glyceraldehyde (GLA) and dihydroxyacetone (DHA), on metal-organic frameworks using density functional theory calculations. The reaction mechanism proceeds through two main steps: first, the opening of the fructose ring; second, the retro-aldol fragmentation, which is favored over intramolecular hydrogen shifts. The substitution of a tetravalent metal in the metal-organic framework leads to different adsorption strengths in the order Hf-NU-1000 > Zr-NU-1000 > Ti-NU-1000. The catalytic activities of Hf-NU-1000 and Zr-NU-1000 are found to be similar. Both are more active than Ti-NU1000, corresponding to their relative Lewis acidity. It was found that functionalization of the organic linkers of the Hf-NU-1000 MOF does not improve its catalytic activity. The catalytic activity follows the order Hf-MOF-808 > Hf-NU-1000 > Hf-UIO-66 when based on either the overall activation energy or the turnover frequency (TOF).

Production of Methyl Lactate with Sn-USY and Sn-β: Insights into Real Hemicellulose Valorization

Potassium exchanged Sn-β and Sn-USY zeolites have been tested for the transformation of various aldoses (hexoses and pentoses), exhibiting outstanding catalytic activity and selectivity toward methyl lactate. Insights into the transformation pathways using reaction intermediates-dihydroxyacetone and glycolaldehyde-as substrates revealed a very high catalytic proficiency of both zeolites in aldol and retro-aldol reactions, showcasing their ability to convert small sugars into large sugars, and vice versa. This feature makes the studied Sn-zeolites outstanding catalysts for the transformation of a wide variety of sugars into a limited range of commercially valuable alkyl lactates and derivatives. [K]Sn-β proved to be superior to [K]Sn-USY in terms of shape selectivity, exerting tight control on the distribution of produced α-hydroxy methyl esters. This shape selectivity was evident in the transformation of several complex sugar mixtures emulating different hemicelluloses-sugar cane bagasse, Scots pine, and white birch-that, despite showing very different sugar compositions, were almost exclusively converted into methyl lactate and methyl vinyl glycolate in very similar proportions. Moreover, the conversion of a real hemicellulose hydrolysate obtained from Scots pine through a simple GVL-based organosolv process confirmed the high activity and selectivity of [K]Sn-β in the studied transformation, opening new pathways for the chemical valorization of this plentiful, but underutilized, sugar feedstock.

Global trends and future prospects of lactic acid production from lignocellulosic biomass

Lignocellulosic biomass (LCB) stands as a substantial and sustainable resource capable of addressing energy and environmental challenges. This study employs bibliometric analysis to investigate research trends in lactic acid (LA) production from LCB spanning the years 1991 to 2022. The analysis reveals a consistent growth trajectory with minor fluctuations in LA production from LCB. Notably, there's a significant upswing in publications since 2009. Bioresource Technology and Applied Microbiology and Biotechnology emerge as the top two journals with extensive contributions in the realm of LA production from LCB. China takes a prominent position in this research domain, boasting the highest total publication count (736), betweenness centrality value (0.30), and the number of collaborating countries (42), surpassing the USA and Japan by a considerable margin. The author keywords analysis provides valuable insights into the core themes in LA production from LCB. Furthermore, co-citation reference analysis delineates four principal domains related to LA production from LCB, with three associated with microbial conversion and one focused on chemical catalytic conversion. Additionally, this study examines commonly used LCB, microbial LA producers, and compares microbial fermentation to chemical catalytic conversion for LCB-based LA production, providing comprehensive insights into the current state of this field and suggesting future research directions.

Distinct Selectivity Control in Solar-Driven Bio-Based α-Hydroxyl Acid Conversion: A Comparison of Pt Nanoparticles and Atomically Dispersed Pt on CdS

Solar-driven photocatalytic lignocellulose conversion is a promising strategy for the sustainable production of high-value chemicals, but selectivity control remains a challenging goal in this field. Here, we report efficient and selective conversion of lignocellulose-derived α-hydroxyl acids to tartaric acid derivatives, α-keto acids, and H2 using Pt-modified CdS catalysts. Pt nanoparticles on CdS selectively produce tartaric acid derivatives via C-C coupling, while atomically dispersed Pt on CdS switches product selectivity to the oxidation reaction to produce α-keto acids. The atomically dispersed Pt species stabilized by Pt-S bonds promote the activation of the hydroxyl group and thus switch product selectivity from tartaric acid derivatives to α-keto acids. A broad range of lignocellulose-derived α-hydroxyl acids was applied for preparing the corresponding tartaric acid derivatives and α-keto acids over the two Pt-modified CdS catalysts. This work highlights the unique performance of metal sulfides in coupling reactions and demonstrates a strategy for rationally tuning product selectivity by engineering the interaction between metal sulfide and cocatalyst.

Intergrowth Zeolites, Synthesis, Characterization, and Catalysis

Microporous zeolites that can act as heterogeneous catalysts have continued to attract a great deal of academic and industrial interest, but current progress in their synthesis and application is restricted to single-phase zeolites, severely underestimating the potential of intergrowth frameworks. Compared with single-phase zeolites, intergrowth zeolites possess unique properties, such as different diffusion pathways and molecular confinement, or special crystalline pore environments for binding metal active sites. This review first focuses on the structural features and synthetic details of all the intergrowth zeolites, especially providing some insightful discussion of several potential frameworks. Subsequently, characterization methods for intergrowth zeolites are introduced, and highlighting fundamental features of these crystals. Then, the applications of intergrowth zeolites in several of the most active areas of catalysis are presented, including selective catalytic reduction of NOx by ammonia (NH3-SCR), methanol to olefins (MTO), petrochemicals and refining, fine chemicals production, and biomass conversion on Beta, and the relationship between structure and catalytic activity was profiled from the perspective of intergrowth grain boundary structure. Finally, the synthesis, characterization, and catalysis of intergrowth zeolites are summarized in a comprehensive discussion, and a brief outlook on the current challenges and future directions of intergrowth zeolites is indicated.

Tracking Lattice Distortion Induced by Defects and Framework Tin in Beta Zeotypes

The use of powder X-ray diffraction (PXRD) coupled with lattice parameter refinement is used to investigate the crystal structure of Sn-Beta materials. A newly developed semiempirical PXRD model with a reduced tetragonal unit cell is applied to obtain the characteristic crystallographic features. There is a robust correlation between lattice parameters and the concentration of tin and defects for materials prepared via hydrothermal (HT) and postsynthetic (PT) methods. With tin incorporation, PT Sn-Beta samples, which possess a more defective structure, exhibit an extended interlayer distance in the stacking sequence and expansion of the translation symmetry within the layers, leading to larger unit cell dimensions. In contrast, HT Sn-Beta samples, having fewer defects, show a minimal effect of tin site density on the unit cell volume, whereas lattice distortion is directly correlated to the framework tin density. Furthermore, density functional theory (DFT) studies support an identical trend of lattice distortion following the monoisomorphous substitution of T sites from silicon to tin. These findings highlight that PXRD can serve as a rapid and straightforward characterization method to evaluate both framework defects and heteroatom density, offering a novel approach to monitor structural changes and the possibility to evaluate the catalytic properties of heteroatom-incorporated zeotypes.

Computational Study of the Solid-State Incorporation of Sn(II) Acetate into Zeolite β

Sn-doped zeolites are potent Lewis acid catalysts for important reactions in the context of green and sustainable chemistry; however, their synthesis can have long reaction times and harsh chemical requirements, presenting an obstacle to scale-up and industrial application. To incorporate Sn into the β zeolite framework, solid-state incorporation (SSI) has recently been demonstrated as a fast and solvent-free synthetic method, with no impairment to the high activity and selectivity associated with Sn-β for its catalytic applications. Here, we report an ab initio computational study that combines periodic density functional theory with high-level embedded-cluster quantum/molecular mechanical (QM/MM) to elucidate the mechanistic steps in the synthetic process. Initially, once the Sn(II) acetate precursor coordinates to the β framework, acetic acid forms via a facile hydrogen transfer from the β framework onto the monodentate acetate ligand, with low kinetic barriers for subsequent dissociation of the ligand from the framework-bound Sn. Ketonization of the dissociated acetic acid can occur over the Lewis acidic Sn(II) site to produce CO2 and acetone with a low kinetic barrier (1.03 eV) compared to a gas-phase process (3.84 eV), helping to explain product distributions in good accordance with experimental analysis. Furthermore, we consider the oxidation of the Sn(II) species to form the Sn(IV) active site in the material by O2- and H2O-mediated mechanisms. The kinetic barrier for oxidation via H2 release is 3.26 eV, while the H2O-mediated dehydrogenation process has a minimum barrier of 1.38 eV, which indicates the possible role of residual H2O in the experimental observations of SSI synthesis. However, we find that dehydrogenation is facilitated more significantly by the presence of dioxygen (O2), introduced in the compressed air gas feed, via a two-step process oxidation process that forms H2O2 as an intermediate and has greatly reduced kinetic barriers of 0.25 and 0.26 eV. The results provide insight into how Sn insertion into β occurs during SSI and demonstrate the possible mechanism of top-down synthetic procedures for metal insertion into zeolites.

Scalable electrosynthesis of commodity chemicals from biomass by suppressing non-Faradaic transformations

Electrooxidation of biomass platforms provides a sustainable route to produce valuable oxygenates, but the practical implementation is hampered by the severe carbon loss stemming from inherent instability of substrates and/or intermediates in alkaline electrolyte, especially under high concentration. Herein, based on the understanding of non-Faradaic degradation, we develop a single-pass continuous flow reactor (SPCFR) system with high ratio of electrode-area/electrolyte-volume, short duration time of substrates in the reactor, and separate feeding of substrate and alkaline solution, thus largely suppressing non-Faradaic degradation. By constructing a nine-stacked-modules SPCFR system, we achieve electrooxidation of glucose-to-formate and 5-hydroxymethylfurfural (HMF)-to-2,5-furandicarboxylic acid (FDCA) with high single-pass conversion efficiency (SPCE; 81.8% and 95.8%, respectively) and high selectivity (formate: 76.5%, FDCA: 96.9%) at high concentrations (formate: 562.8 mM, FDCA: 556.9 mM). Furthermore, we demonstrate continuous and kilogram-scale electrosynthesis of potassium diformate (0.7 kg) from wood and soybean oil, and FDCA (1.17 kg) from HMF. This work highlights the importance of understanding and suppressing non-Faradaic degradation, providing opportunities for scalable biomass upgrading using electrochemical technology.

Engineering Lewis Acidity in Zeolite Catalysts by Electrochemical Release of Heteroatoms during Synthesis

The creation of heteroatom nodes in zeolite frameworks is a challenging but rewarding pathway to superior materials for numerous catalytic applications. Here, we present a novel method for precise control over heteroatom incorporation by in situ anodic release of a desired metal during hydrothermal zeolite synthesis. The generic character of the technique and the applicability of the new synthesis reactor are shown across 3 zeolite structures crystallized and 4 electrode metals in two pH zones and by offering access to a new mixed-metal zeolite. The timed and voltage-controlled metal release offers a minimized interference between the metal precursor state and critical events in the zeolite's crystallization. A mechanistic study for Sn-MFI revealed the key importance of controlled release: while keeping its concentration lower than in batch, a lot more Sn can be incorporated into the framework. The method grants access to 10× increased framework Lewis acid site densities (vs batch controls) for the most relevant stannosilicates. As a proof, the electro-made materials demonstrate higher productivity than their classic counterparts in lactate catalysis. This innovative approach effectively expands the synthesis space of zeolites.

Catalytic Conversion of Sugars into Lactic Acid via a RuOx/MoS2 Catalyst

The catalytic transformation of sugars into lactic acid has shown great potential for the scalable utilization of renewable biomass. Herein, RuOx/MoS2 catalysts were synthesized with the assistance of CaO for the one-pot conversion of glucose to lactic acid. Under the reaction conditions of 120 °C and 1MPa O2, a 96.6% glucose conversion and a 54.3% lactic acid yield were realized in the one-pot catalytic reaction, with relatively high stability after four successive cycles. This catalytic system was also effective for the conversion of many other carbohydrate substrates, such as fructose, xylose and cellulose (selectivity 68.9%, 78.2% and 50.6%, respectively). According to catalyst characterizations and conditional experiments, the highly dispersed RuOx species on the surface of MoS2, together with OH−, promoted isomerization, retro-aldol condensation, dehydration and hydration reactions, resulting in a relatively high lactic acid yield for sugar conversions.

Sustainable Synthesis of α-Hydroxycarboxylic Acids by Manganese Catalyzed Acceptorless Dehydrogenative Coupling of Ethylene Glycol and Primary Alcohols

Herein, we report a straightforward synthesis of valuable α-hydroxycarboxylic acid molecules via an acceptorless dehydrogenative coupling of ethylene glycol and primary alcohols. A bench-stable manganese complex catalyzed the reaction, which is scalable, with the product being isolated with high yields and selectivities under mild conditions. The protocol is environmentally benign, producing water and hydrogen gas as the only byproducts. Methanol can also be used as a C1 source for producing the platform molecule lactic acid, with a high turnover of >10⁴ . The methodology was also used to functionalize alcohols derived from natural products and fatty acids. Furthermore, it was applied for synthesizing α-amino acid, α-thiocarboxylic acid, and several drugs and bioactive molecules, including endogenous metabolites, Danshensu, Enalapril, Lisinopril, and Rosmarinic acid. Preliminary mechanistic studies were performed to shed light on the mechanism involved in the reaction.

Niobium: The Focus on Catalytic Application in the Conversion of Biomass and Biomass Derivatives

The world scenario regarding consumption and demand for products based on fossil fuels has demonstrated the imperative need to develop new technologies capable of using renewable resources. In this context, the use of biomass to obtain chemical intermediates and fuels has emerged as an important area of research in recent years, since it is a renewable source of carbon in great abundance. It has the benefit of not contributing to the additional emission of greenhouse gases since the CO2 released during the energy conversion process is consumed by it through photosynthesis. In the presented review, the authors provide an update of the literature in the field of biomass transformation with the use of niobium-containing catalysts, emphasizing the versatility of niobium compounds for the conversion of different types of biomass.

Catalytic production of 1,2-propanediol from sucrose over a functionalized Pt/deAl-beta zeolite catalyst

To eliminate the dependence on fossil fuels and expand the applications of biomass conversion, an efficient Pt/deAl-beta@Mg(OH)₂ catalyst was designed, with dealuminated beta zeolite loaded with Pt as the core and Mg(OH)₂ as the shell. The catalyst was used to produce 1,2-propanediol (1,2-PDO) from sucrose. The preparation and reaction conditions of the catalyst were optimized. The optimal yield of 1,2-PDO was 33.5% when the conditions were 20 h of dealumination, 3.0 wt% Pt loading, 5.0 wt% Mg(OH)₂, 200 mg of catalyst, 10 mL (11.25 mg mL^-1) of sucrose solution, an initial H₂ pressure of 6 MPa, 200 °C, and 3 h. The core-shell structure of the modified beta zeolite shows good stability, yielding more than 30.0% after three cycles of reuse. Firstly, the molecular zeolite can host more acid sites after dealumination by concentrated nitric acid and this can prolong the catalyst's service life. Secondly, the loading of Pt increases the distribution of acid sites and improves the shape selectivity of the catalyst. The introduction of alkali produces many alkaline sites, inhibits the occurrence of side reactions, and increases the product yield. The above modification methods increase the production of 1,2-PDO by promoting isomerization between glucose and fructose from sucrose hydrolysis and the reverse aldol condensation (RAC) reaction. This paper provides a theoretical basis and reference route for applying biomass conversion technology in practical production, which is of great significance for developing biomass resources into high-value-added chemical products.

Glucose Hydrogenolysis into 1,2-Propanediol Using a Pt/deAl@Mg(OH)2 Catalyst: Expanding the Application of a Core-Shell Structured Catalyst

To substitute fossil resources, it is necessary to investigate the conversion of biomass into 1,2-propanediol (1,2-PDO) as a high-value-added chemical. The Pt/deAl-Beta@Mg(OH)₂ catalytic system is designed to obtain a higher 1,2-PDO production yield. The optimal yield of 1,2-PDO is 34.1%. The unique shell-core structure of the catalyst demonstrates stability, with a catalytic yield of over 30% after three times of use. The primary process path from glucose to 1,2-PDO, glucose-hexitol-1,2-PDO, is speculated by the experiments of intermediate product selectivity. The alkaline catalytic mechanism of the reaction process is elucidated by studying catalyst characterization and analyzing different time courses of products. The introduction of Mg(OH)₂ improves the target yield by promoting the isomerization from glucose to fructose and retro-aldol condensation (RAC) conversion, with pseudo-yield increases of 76.1% and 42.1%, respectively. By studying the processes of producing lactic acid and 1,2-PDO from glucose, the glucose hydrogenolysis flow chart is improved, which is of great significance for accurately controlling 1,2-PDO production in industrial applications. The metal, acid, and alkali synergistic catalytic system constructed in this paper can provide a theoretical basis and route reference for applying biomass conversion technology in practice.

A unified view on catalytic conversion of biomass and waste plastics

Originating from the desire to improve sustainability, producing fuels and chemicals from the conversion of biomass and waste plastic has become an important research topic in the twenty-first century. Although biomass is natural and plastic synthetic, the chemical nature of the two are not as distinct as they first appear. They share substantial structural similarities in terms of their polymeric nature and the types of bonds linking their monomeric units, resulting in close relationships between the two materials and their conversions. Previously, their transformations were mostly studied and reviewed separately in the literature. Here, we summarize the catalytic conversion of biomass and waste plastics, with a focus on bond activation chemistry and catalyst design. By tracking the historical and more recent developments, it becomes clear that biomass and plastic have not only evolved their unique conversion pathways but have also started to cross paths with each other, with each influencing the landscape of the other. As a result, this Review on the catalytic conversion of biomass and waste plastic in a unified angle offers improved insights into existing technologies, and more importantly, may enable new opportunities for future advances.

Efficient Catalytic Conversion of Glucose into Lactic Acid over Y-β and Yb-β Zeolites

In this work, a new type of modified β zeolites with rare earth elements (ree) was discovered for producing lactic acid from glucose and achieved a good catalytic effect. At first, the catalytic performances of ree-β zeolites, ree oxides, and single-transition-metal-β zeolites were compared, and the result showed that Y-β and Yb-β zeolites had the best catalytic activity under the same reaction conditions. Under the best reaction conditions, the maximum yields of lactic acid with Y-β and Yb-β catalysts were 45.3 and 43.6%, respectively. The acid characterization showed that Y/Yb-β zeolites had a similar number of Lewis acid sites as Sn-β zeolites, and they were also more than other transition-metal-β zeolites. Thus, Y-β and Yb-β zeolites had a higher lactic acid yield than those catalysts. It is interesting to note that Y-β and Yb-β zeolites owned more Brønsted acids but produced fewer byproducts. Combining the decomposition experiment of 5-hydroxymethyl furfural, fewer byproducts were produced with Y-β and Yb-β zeolites because the low amount of Brønsted acid contained could hinder the decomposition of 5-hydroxymethyl furfural, thereby slowing down the side reaction.

Defect-Guided Synthesis of Hierarchical Sn-B-Beta Zeolite with Highly Exposed Sn Sites

Selectively anchoring active centers on the external surface for forming highly exposed acid sites is a highly desirable but challenging task in zeolite catalyst synthesis. Herein, a defect-guided etching-regrowth strategy is rationally designed for facilely positioning Sn Lewis acid sites on the outer surface of the Sn-B-Beta while fabricating a bifunctional hierarchical structure. The synthesis was conducted by hydrothermal treatment of the as-made B-Beta (uncalcined), which has intrinsic defects of the BEA structure, with Sn source and basic organic structure directing agent (SDA). Under a moderate SDA concentration, with blocked micropore channels, such SDA-triggered etching-regrowth will proceed along the defect defined pathway, which ensures Sn selectively anchored on the external surface. Moreover, this methodology has exclusively introduced tetrahedrally coordinated framework Sn with open Sn sites as the predominated species. Mono- and disaccharide isomerizations in ethanol over different Sn-Beta catalysts proved the prominent advantages of the hierarchical structure with highly exposed and synergetic acid sites.

Synergetic Effect of Mo, Mg-Modified Sn-β Over Moderate-Temperature Conversion of Hexose to Alkyl Lactate

The thermocatalytic conversion of hexose into valuable chemicals such as methyl lactate under mild conditions is very appealing. Here, we report that Mo, Mg co-modified Sn-β catalyst can effectively catalyze the transformation of glucose and fructose into alkyl lactate at moderate temperatures. A maximum yield of around 35% of methyl lactate was achieved from the conversion of glucose in methanol at 100°C over Sn-β catalyst modified with 3 wt% Mo and 0.5 wt% Mg. However, up to 82.8% yield of ethyl lactate was obtained in the case of fructose in ethanol upon the same catalytic condition, suggesting a significant solvent effect. The Mo species plays a key role to enable the retro-aldol condensation of fructose, in which the competing side reactions are significantly suppressed with the assistance of neighboring Mg species probably through a synergetic effect of Lewis acid-base.

Efficient Conversion of Glucose to Methyl Lactate with Sn-USY: Retro-aldol Activity Promotion by Controlled Ion Exchange

Sn-USY materials have been prepared through an optimized post-synthetic catalytic metalation procedure. These zeolites displayed, upon ion exchange with alkaline metals, an outstanding activity in the direct transformation of glucose into methyl lactate, yielding more than 70% of the starting glucose as the target product, and an overall combined retro-aldol condensation product yield above 95% in a short reaction time (<4 h). This outstanding catalytic performance is ascribed to the neutralization of Brønsted acid sites, the consequent depression of side reactions, and a higher population of tin open sites in the ion-exchanged Sn-USY zeolites. Reusability tests evidenced some loss of catalytic activity, partially caused by the closing of tin sites, although the use of small amounts of water in the reaction media demonstrated that this deactivation mechanism can be, at least, partially alleviated.

Enhanced catalytic activity of layered double hydroxides via in-situ reconstruction for conversion of glucose/food waste to methyl lactate in biorefinery

Conversion of food waste into valuable chemicals under mild conditions has attracted increasing attention. Herein, a series of nano-sized MgAl layered double hydroxides (LDHs) were firstly developed as solid base catalyst for the methyl lactate (MLA) production directly from glucose/food waste. Glucose, which could be easily obtained from cellulose or starch-rich food waste via hydrolysis, was thus selected as the model compound. It is inspiring to find that the metal hydroxide layer in prepared LDHs was highly stable and suitable enlarged interlayer distance was reconstructed owing to in-situ intercalation of formed aromatics during the reaction, which was demonstrated by ²⁷Al magic angle spinning nuclear magnetic resonance and time-of-flight secondary ion mass spectrometry analysis. As a result, in-situ activation of the catalysts along with gradually enhanced catalytic activity was obtained in the recycling runs and the highest MLA yield of 47.6% from glucose was achieved over LDHs (5:1) after 5 runs at 150 °C. Most importantly, the scope was further extended to other typical substrates (e.g. Chinese cabbage and rice) and the results demonstrated the effectiveness of present conversion system for real food waste.

Photocatalytic Conversion of Fructose to Lactic Acid by BiOBr/Zn@SnO2 Material

Photocatalysis provides a prospective approach for achieving high-value products under mild conditions. To realize this, constructing a selective, low-cost and environmentally friendly photocatalyst is the most critical factor. In this study, BiOBr/Zn@SnO2 is fabricated by a one-pot hydrothermal synthesis method and BiOBr: SnO2 ratio is 3:1; this material is applied as photocatalyst in fructose selective conversion to lactic acid. The bandgap structure can be regulated via two-step modification, which includes Zn doping SnO2 and Zn@SnO2 coupling BiOBr. The photocatalyst shows excellent conversion efficiency in fructose and high selectivity in lactic acid generation under alkaline conditions. The conversion rate is almost 100%, and the lactic acid yield is 79.6% under optimal reaction conditions. The catalyst is highly sustainable in reusability; the lactic acid yield can reach 67.4% after five runs. The possible reaction mechanism is also proposed to disclose the photocatalysis processes.

Catalytic amination of lactic acid using Ru-zeolites

In this work we investigate the synthesis of alanine from lactic acid, a biobased platform chemical, using ammonia as a nitrogen source and Ru/zeolite catalysts. We report a high alanine selectivity when using Ru/BEA of 80-93%. Reaction side products were identified as ethanol, propionic acid or propanamide and the reaction mechanism was investigated. We further optimised reaction conditions resulting in turn over numbers five times higher than previously reported and could reduce Ru leaching by 30-40%. However, leaching and catalyst stability remains a concern. Furthermore, we critically analyse the benefits of Ru/zeolites versus their stability under the basic, high temperature reaction conditions.

Catalytic conversion of waste corrugated cardboard into lactic acid using lanthanide triflates

The efficient strategy for waste conversion and resource recovery is of great interest in the sustainable bioeconomy context. This work reports on the catalytic upcycling of waste corrugated cardboard (WCC) into lactic acid using lanthanide triflates catalysts. WCC, a primary contributor to municipal solid wastes, has been viewed as a feedstock for producing a wide range of renewable products. Hydrothermal conversion of WCC was carried out in the presence of several lanthanide triflates. The reaction with erbium(III) triflate (Er(OTf)₃) and ytterbium(III) triflate (Yb(OTf)₃) resulted in high lactic acid yields, 65.5 and 64.3 mol%, respectively. In addition, various monomeric phenols were readily obtained as a co-product stream, opening up opportunities in waste management and resource recovery. Finally, technoeconomic analysis was conducted based on the experimental results, which suggests a significant economic benefit of chemocatalytic upcycling of WCC into lactic acid.

Catalytic Conversion of High Fructose Corn Syrup to Methyl Lactate with CoO@silicalite-1

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.

High-Productivity Continuous Conversion of Glucose to α-Hydroxy Esters over Postsynthetic and Hydrothermal Sn-Beta Catalysts

The retro-aldol fragmentation of glucose is a complex reaction of industrial relevance, which provides a potentially sustainable route for the production of α-hydroxyester compounds of relevance to the green polymer industry, such as methyl lactate and methyl vinyl glycolate. Although the zeolite catalyst, Sn-Beta, has shown itself to be a promising catalyst for this process, important information concerning the stability of the catalyst during continuous operation is not yet known, and improvements to its yield of retro-aldol products are also essential. Here, we perform detailed spectroscopic studies of a selection of Sn-Beta catalysts and evaluate their performances for the retro-aldol fragmentation of glucose under continuous processing conditions, with the dual aims of developing new structure-activity-lifetime relationships for the reaction and maximizing the productivity and selectivity of the process. Kinetic studies are performed under both established reaction conditions and in the presence of additional promoters, including water and alkali salts. Generally, this study demonstrates that the reaction conditions and choice of catalyst cannot be optimized in isolation, since each catalyst explored in this study responds differently to each particular process perturbation. However, by evaluating each type of the Sn-Beta catalyst under each set of reaction conditions, we reveal that postsynthetic Sn-Beta catalysts exhibit the best levels of performance when activity, selectivity, and stability are taken into account. Specifically, the best levels of performance are obtained with a postsynthetic Sn-Beta catalyst that is preactivated in a flow of methanol prior to reaction, which provides α-hydroxyester yields over 90% at the early stages of continuous operation and operates at high yield and selectivity for over 60 h on stream. Space-time-yields over two orders of magnitude higher than any previously reported for this reaction are achieved, setting a new benchmark in terms of the retro-aldol fragmentation of glucose.

Sn-Beta Catalyzed Transformations of Sugars—Advances in Catalyst and Applications

Beta zeolite modified with Sn in the framework (Sn-Beta) was synthesized and introduced as a heterogeneous catalyst for Baeyer–Villiger oxidations about twenty years ago. Since then, both syntheses strategies, characterization and understanding as well as applications with the material have developed significantly. Remarkably, Sn-Beta zeolite has been discovered to exhibit unprecedented high catalytic efficiency for the transformation of glucose to fructose (i.e., aldoses to ketoses) and lactic acid derivatives in both aqueous and alcoholic media, which has inspired an extensive interest to develop more facile and scalable syntheses routes and applications for sugars transformations. This review survey the progress made on both syntheses approaches of Sn-Beta and applications of the material within catalyzed transformations of sugar, including bottom-up and top-down syntheses and catalyzed isomerization, dehydration, and fragmentation of sugars.

Identification of Cooperative Reaction Sites in Metal-Organic Framework Catalysts for High Yielding Lactic Acid Production from d-Xylose

Determining the roles of surface functionality of heterogeneous acid catalysts is important for many industrial catalysts. In this study, the decisive structure of metal-organic frameworks (MOFs) is utilized to identify important features for the effective conversion of d-xylose into lactic acid. Several acidic MOFs are tested and the combination of Lewis acidity and adjacent hydroxy sites is found to be critical to attain high lactic acid yields. This hypothesis is corroborated experimentally by modification of the MOF to increase such sites, which affords an enhanced lactic acid yield of 79 %, and investigation of the acidity by using in situ FTIR spectroscopy. Density functional theory calculations disclose the cooperative behavior of Lewis acid sites and hydroxy groups in promoting the Cannizzaro reaction, a key step in the production of lactic acid.

Mesoporous Sn-In-MCM-41 Catalysts for the Selective Sugar Conversion to Methyl Lactate and Comparative Life Cycle Assessment with the Biochemical Process

The use of biomass for the production of energy and higher added value products is a topic of increasing interest in line with growing environmental concerns and circular economy. Mesoporous material Sn-In-MCM-41 was synthesized for the first time and used as a catalyst for the transformation of sugars to methyl lactate (ML). This catalyst was characterized in depth by various techniques and compared with Sn-MCM-41 and In-MCM-41 catalysts. In the new Sn-In-MCM-41 material, both metals, homogeneously distributed throughout the mesoporous structure of MCM-41, actuate in a cooperative way in the different steps of the reaction mechanism. As a result, yields to ML of 69.4 and 73.9% in the transformation of glucose and sucrose were respectively reached. In the case of glucose, the ML yield 1.5 and 2.6 times higher than those of Sn-MCM-41 and In-MCM-41 catalysts, respectively. The Sn-In-MCM-41 catalyst was reused in the transformation of glucose up to four cycles without significant loss of catalytic activity. Finally, life cycle assessment comparison between chemical and biochemical routes to produce ML allowed us to conclude that the use of Sn-In-MCM-41 reduces the environmental impacts compared to Sn-MCM-41. Nevertheless, to make the chemical route comparable to the biochemical one, improvements in the catalyst and ML synthesis have to be achieved.

Designing Sites in Heterogeneous Catalysis: Are We Reaching Selectivities Competitive With Those of Homogeneous Catalysts?

A critical review of different prominent nanotechnologies adapted to catalysis is provided, with focus on how they contribute to the improvement of selectivity in heterogeneous catalysis. Ways to modify catalytic sites range from the use of the reversible or irreversible adsorption of molecular modifiers to the immobilization or tethering of homogeneous catalysts and the development of well-defined catalytic sites on solid surfaces. The latter covers methods for the dispersion of single-atom sites within solid supports as well as the use of complex nanostructures, and it includes the post-modification of materials via processes such as silylation and atomic layer deposition. All these methodologies exhibit both advantages and limitations, but all offer new avenues for the design of catalysts for specific applications. Because of the high cost of most nanotechnologies and the fact that the resulting materials may exhibit limited thermal or chemical stability, they may be best aimed at improving the selective synthesis of high value-added chemicals, to be incorporated in organic synthesis schemes, but other applications are being explored as well to address problems in energy production, for instance, and to design greener chemical processes. The details of each of these approaches are discussed, and representative examples are provided. We conclude with some general remarks on the future of this field.

Single-Step Sustainable Production of Hydroxy-Functionalized 2-Imidazolines from Carbohydrates

Manufacturing valuable N-containing chemicals from biomass is highly desirable yet challenging. Herein, a novel strategy was developed for efficient production of 2-(1-hydroxyethyl)-imidazoline (HI), a high-value and versatile building block for synthesizing a myriad of bioactive targets, directly from carbohydrates under mild reaction conditions. With this strategy, bio-based HI was produced from fructose in one step with as high as 77 C % isolated yield in the presence of ethylenediamine (EDA) and InCl₃ at 130 °C. The synergistic functions of EDA and InCl₃ were identified for the transformation, wherein EDA promoted the scission of C-C bond of fructose backbone via retro-aldol (R-A) reaction and rapidly trapped in-situ formed reactive carbonyl-containing C₃ intermediate for HI formation to avoid undesired side reaction, and InCl₃ facilitated the formation of this C₃ intermediate and the final 1,2-hydrid shift step.

Catalytic production of low-carbon footprint sustainable natural gas

Natural gas is one of the foremost basic energy sources on earth. Although biological process appears as promising valorization routes to transfer biomass to sustainable methane, the recalcitrance of lignocellulosic biomass is the major limitation for the production of mixing gas to meet the natural gas composition of pipeline transportation. Here we develop a catalytic-drive approach to directly transfer solid biomass to bio-natural gas which can be suitable for the current infrastructure. A catalyst with Ni₂Al₃ alloy phase enables nearly complete conversion of various agricultural and forestry residues, the total carbon yield of gas products reaches up to 93% after several hours at relative low-temperature (300 degrees Celsius). And the catalyst shows powerful processing capability for the production of natural gas during thirty cycles. A low-carbon footprint is estimated by a preliminary life cycle assessment, especially for the low hydrogen pressure and non-fossil hydrogen, and technical economic analysis predicts that this process is an economically competitive production process.

Supported metals on porous solids as heterogeneous catalysts for the synthesis of propargylamines

This perspective summarizes recent developments in the synthesis of propargylamines using porous solids (zeolites, MOFs and carbon) as supports/catalysts.