Recent progress in the development of solid catalysts for biomass conversion into high value-added chemicals

Design of Bifunctional Nanocatalysts Based on Zeolites for Biomass Processing

Bifunctional catalysts consisting of metal-containing nanoparticles (NPs) and zeolite supports have received considerable attention due to their excellent catalytic properties in numerous reactions, including direct (biomass is a substrate) and indirect (platform chemical is a substrate) biomass processing. In this short review, we discuss major approaches to the preparation of NPs in zeolites, concentrating on methods that allow for the best interplay (synergy) between metal and acid sites, which is normally achieved for small NPs well-distributed through zeolite. We focus on the modification of zeolites to provide structural integrity and controlled acidity, which can be accomplished by the incorporation of certain metal ions or elements. The other modification avenue is the adjustment of zeolite morphology, including the creation of numerous defects for the NP entrapment and designed hierarchical porosity for improved mass transfer. In this review, we also provide examples of synergy between metal and acid sites and emphasize that without density functional theory calculations, many assumptions about the interactions between active sites remain unvalidated. Finally, we describe the most interesting examples of direct and indirect biomass (waste) processing for the last five years.

The Potential of Cellulose as a Source of Bioethanol using the Solid Catalyst: A Mini-Review

One of the most important biofuels is cellulose ethanol which is a popular material for bioethanol production. The present cellulosic ethanol production is through the cellulolytic process and this involves the splitting of complex cellulose into simple sugars through the hydrolysis process of the lignocellulose pretreated with acids and enzymes after which the product is fermented and distilled. There are, however, some challenges due to the enzymatic and acid processes based on the fact that acid hydrolysis has the ability to corrode equipment and cause unwanted waste while the enzymatic hydrolysis process requires a longer time because enzymes are costly and limited. This means there is a need for innovations to minimize the problems associated with these two processes and this led to the application of solid catalysts as the green and effective catalyst to convert cellulose to ethanol. Solid catalysts are resistant to acid and base conditions, have a high surface area, and do not cause corrosion during the conversion of the cellulose due to their neutral pH. This review, therefore, includes the determination of the cellulose potential as feedstock to be used in ethanol production as well as the preparation and application of solid catalyst as the mechanism to convert cellulose into fuel and chemicals. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Synthesis of Sulfonated Porous Organic Polymers with a Hydrophobic Core for Efficient Acidic Catalysis in Organic Transformations

Synthesis of sulfonated porous polymers with improved hydrophobicity and stability is of extreme importance in both academic research and industrial applications. However, there is often a trade-off between acidity and surface hydrophobicity of sulfonated polymers. In this study, we report a strategy for the synthesis of sulfonated porous organic polymers (S-PT) with improved hydrophobicity via free radical polymerization method by using a rigid and large multidentate monomer, 1,3,5-tri(4-vinylphenyl)-benzene, having a hydrophobic core. The results of vapor adsorption measurement show that S-PT has more hydrophobic properties than sulfonated poly(divinylbenzene) (S-PD), attributed to the hydrophobic core of its multidentate monomer. Furthermore, the optimization of sulfonation time established a balance between surface acidity and hydrophobicity. Under optimized conditions, S-PT afforded up to 113 mmol g^-1  h^-1 TOF in the esterification of oleic acid with methanol, more active than commercial Amberlyst-15 with TOF of 15 mmol g^-1  h^-1 and Nafion NR50 with TOF of 7 mmol g^-1  h^-1 . We believe that the findings of this study will provide useful insights to advance the design and synthesis of solid acid catalysts for organic transformations.

Techno-Economic Analysis of a Process for the Aqueous Conversion of Corn Stover into Lactic and Levulinic Acid through Sn-Beta Catalysis

A readily available source for renewable fuels and chemicals is corn stover, which consists of the leftover stalks, leaves, husks, and cobs from the corn plant and makes up nearly half of the yield of a corn crop. Common practice is to pretreat it with sulfuric acid to break down the hemicellulose, releasing xylose, followed by enzymatic hydrolysis to convert the cellulose into glucose. Using a Sn-Beta catalyst, it is possible to convert these monomeric sugars into lactic, levulinic, formic, and acetic acids. This paper presents the results of a techno-economic analysis (TEA) of the commercial feasibility of producing these acids from corn stover. Two preliminary process designs were evaluated which represent two separate reaction yields: a balanced yield of both lactic and levulinic acids and the yields from a co-catalysis with CaSO4 to produce primarily lactic acid. Both process designs are scaled to process 230,000 MT/year of corn stover. An AACS Class 4 factored broad capital cost estimate and comparable estimates of operating costs and revenues were used to generate cash flow sheets to evaluate the economic feasibility of both options. The balanced product process has an estimated NPV@20% = $3.3 million ± 40%, while the CaSO4-facilited process has an NPV@20% = $110 million ± 40% (January 2019 basis). A major hurdle for both processes is the demand for levulinic acid. The balanced product process will produce 135% of the expected global demand and the CaSO4-facilitated alternative will meet 31% of the demand. For the demand to meet production, advances in levulinic acid applications are needed. However, the attractive economics suggest that these technologies warrant further development towards commercialization.

Preparation and catalytic performance of biomass-based solid acid catalyst from Pennisetum sinense for cellulose hydrolysis

As a kind of lignocellulosic biomass, Pennisetum sinense (P. sinense) is commonly used as animal feed, fertilizer or papermaking raw materials. Based on the high carbon content and renewability of P. sinense, we explored the possibility and feasibility of using it as catalyst matrix. The catalyst was produced by sulfonation of char obtained from the carbonization of P. sinense at 550 °C. The structure of the catalyst was characterized by SEM, BET, XRD, FT-IR, XPS and TGA, and its catalytic performance for the hydrolysis of cellulose was investigated in detail. The highest acidity of the catalyst was 3.79 mmol/g and the maximum glucose yield of 59.92% was achieved under optimized conditions. The catalyst also showed a promising reusability. The glucose yield was 53.01% after 5 cycles and as high as 55.92% when using the regenerated catalyst.

Catalytic Formation of Lactic and Levulinic Acids from Biomass Derived Monosaccarides through Sn-Beta Formed by Impregnation

In the present study, the use of Sn-Beta zeolite to facilitate the conversion of lignocellulosic biomass-derived glucose and xylose into lactic and levulinic acid was explored. The reactions were carried out in a batch reactor using water as the solvent. Water is the preferred solvent over methanol as it reduces downstream product acid recovery and purification complexity. Optimization experiments were performed for reaction temperature and residence time. Under optimized reaction conditions, the Sn-Beta facilitated reaction of a pure sugar solution resulted in lactic acid yields of 13 and 19 wt% of inlet carbon of glucose and xylose, respectively, plus levulinic acid yields of 18 and 0.8 wt%, respectively. When actual biomass-derived sugar solutions were tested, the yields of lactic acid were significantly higher than those from the optimized model solution experiments with lactic acid yields of 34 wt%. These biomass-derived sugar solutions contained residual levels of CaSO4 from the neutralization step of the hydrolysis process. Further experiments were performed to examine the potential effects from CaSO4 contributing to this increase. It was found that the sulfate ions increased the Brønsted basicity and the calcium increased the Lewis acidity of the reaction solution, and that the combination of both effects increased the conversion of the original sugars into lactic acid. These effects were verified by testing other organic bases to isolate the Brønsted acid neutralization effect and the Lewis acid enhancement effect. The addition of CaSO4 resulted in attractive lactic acid yields, 68 wt% and 50 wt% of inlet carbon from pure glucose and xylose solutions, respectively. Increasing the actual corn stover and forage sorghum derived sugars concentration (in water) allowed lactic acids yields of greater than 60 wt% to be achieved. When the optimized Sn-Beta reaction system was applied to corn stover and forage sorghum mixtures, it was found that the ratio of lactic-to-levulinic acid generated was inversely dependent upon the glucose-to-xylose ratio in the recovered sugar mixture.

Influence of Heterogeneous Catalysts and Reaction Parameters on the Acetylation of Glycerol to Acetin: A Review

Glycerol, a polyhydric alcohol, is currently receiving greater attention worldwide in view of its glut in the market occasioned by the recent upsurge in biodiesel production. The acetylation of glycerol to acetin (acetyl glycerol) is one of the many pathways of upgrading glycerol to fine chemicals. Acetin, which could be mono, di, and or triacetin, has versatile applications in the cosmetics, medicines, food, polymer, and fuel industries as a humectant, emulsifier, plasticizer, and fuel additive and so it is of high economic value. Given the critical role of catalysts in green chemistry, this paper reports the influence of the different heterogeneous catalysts used in glycerol acetylation. It also reviewed the influence of catalyst load, temperature, molar ratio, and the time on the reaction.

Production of 5-(formyloxymethyl)furfural from biomass-derived sugars using mixed acid catalysts and upgrading into value-added chemicals

In this work, 5-(formyloxymethyl)furfural (FMF) has been produced from biomass-derived hexose sugars within a biphasic reaction mixture consisting of aqueous formic acid (85%), a strong Brønsted acid catalyst, and 1,2-dichloroethane as an organic extractant. Using a combination of aqueous hydrobromic acid and formic acid, under optimized condition (80 °C, 8 h, 10 wt% substrate loading), 68% isolated yield of FMF was obtained from fructose. FMF has been demonstrated as a renewable chemical building block for the synthesis of renewable chemicals of commercial significance such as 5-methylfurfural, 2,5-diformylfuran, and 2,5-furandicarboxylic acid in good to excellent isolated yields.

Spiky-shaped niobium pentoxide nano-architecture: highly stable and recoverable Lewis acid catalyst

Niobium pentoxide particles with a complex three-dimensional (3D) nanostructure consisting of a spiky structure have been developed as recyclable and recoverable Lewis acid catalysts. The morphology of the niobium pentoxide was successfully controlled from 1D to 3D via a bridging-ligand-assisted hydrothermal treatment, without changing the crystal structure. Compared with dispersed one-dimensional (1D) niobium pentoxide nanorods with a major-axis length and minor-axis length of 20 nm and 5-8 nm, respectively, the spiky-shaped niobium pentoxide composed of 300 nm spherical cores and nanorods with a minor-axis length of 5 nm maintained its surface nanostructure even after calcination at 400 °C in air. The 400 °C-calcined spiky particles exhibited the highest production rate of 2-((4-methoxyphenyl)amino)-2-phenylacetonitrile (0.115 mmol m^-2) in a Strecker reaction, resulting in a nanoscale and ordered surface structure of spiky particles that simultaneously exhibit high specific reactivity and high structural stability. Acid site analysis and Raman spectroscopy revealed that stable nanorods that grew in the (001) orientation functioned as Lewis acid catalysts and that the origin of the acidity was a flexible Nb-O polyhedral structure in the single-nanoscale (<10 nm) niobium oxide rods. This study proposes that the spiky-shaped niobium pentoxide exhibits sintering resistivity and high activity and has potential applications as a recoverable and recyclable solid acid catalyst.

Role of Brønsted and Lewis acidic sites in sulfonated Zr-MCM-41 for the catalytic reaction of cellulose into 5-hydroxymethyl furfural

A series of sulfonated Zr-MCM-41 samples were synthesized by the in-situ method followed by sulfonation using sulfuric acid for the catalytic study of cellulose to 5-hydroxymethyl furfural in batch condition. All synthesized catalysts were characterized by XRD, N2 adsorption–desorption isotherm, FT-IR, TEM, EDX, and NH3 temperature-programmed desorption analysis. The XRD and N2 adsorption–desorption isotherm results have confirmed that incorporated Zr4+ was substituted within the framework of silica MCM-41 with hexagonal pores. Similarly, the FT-IR and EDX results have proved that Zr-MCM-41 was sulfonated. The Brønsted acidic and Lewis acidic sites were identified by NH3-TPD analysis. Among the sulfonated Zr-MCM-41 catalysts, S-15Zr-MCM-41 has shown 70% cellulose conversion with 16.4% selectivity of 5-hydroxymethyl furfural at 170 °C for 2 h which was higher than other catalysts. It was attributed to the high ratio of Brønsted acidic to Lewis acidic sites.

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Functionalized Metal-Organic Framework Catalysts for Sustainable Biomass Valorization

Currently, pristine and functionalized metal-organic frameworks (MOFs) are introduced in heterogeneous catalysis for biomass upgrading owing to the specific texture properties including regular higher-order structure, high specific surface area, and the precisely tailored diversity. The purpose of this review is to afford a comprehensive discussion of the most applications in biomass refinery. We highlight recently developed four types of MOFs like pristine MOFs and their composites, MOF-supported metal NPs, acid-functionalized MOFs, and biofunctionalized MOFs for production of green, sustainable, and industrially acceptable biomass-derived platform molecules: (1) upgrading of saccharides, (2) upgrading of furan derivatives, and (3) upgrading of other biobased compounds.

Oxygen-atom vacancy formation and reactivity in polyoxovanadate clusters

Overview of recent work detailing oxygen-deficient polyoxovanadate clusters as models for reducible metal oxides: toward gaining a fundamental understanding the consequences of vacancy formation on metal oxide surfaces during catalysis.

Selective Transformations of Triglycerides into Fatty Amines, Amides, and Nitriles by using Heterogeneous Catalysis

The use of triglycerides as an important class of biomass is an effective strategy to realize a more sustainable society. Herein, three heterogeneous catalytic methods are reported for the selective one-pot transformation of triglycerides into value-added chemicals: i) the reductive amination of triglycerides into fatty amines with aqueous NH₃ under H₂ promoted by ZrO₂ -supported Pt clusters; ii) the amidation of triglycerides under gaseous NH₃ catalyzed by high-silica H-beta (Hβ) zeolite at 180 °C; iii) the Hβ-promoted synthesis of nitriles from triglycerides and gaseous NH₃ at 220 °C. These methods are widely applicable to the transformation of various triglycerides (C₄ -C₁₈ skeletons) into the corresponding amines, amides, and nitriles.

Metal Oxides in Heterogeneous Oxidation Catalysis: State of the Art and Challenges for a More Sustainable World

This Review presents current knowledge, recent results, and challenges for the future in heterogeneous oxidation catalysis in liquid and gaseous phases on solid metal oxide catalysts. Metal oxides that are used as catalysts and their main structures and properties are summarized, as well as their catalytic properties in selective and total oxidation reactions, which were studied intensively, experimentally and theoretically, by Professor Jerzy Haber during his scientific life. Some emphasis is placed on the classical and unusual catalyst activation procedures for improving catalytic properties for better efficiency. For a more sustainable world, several examples are given of the oxidation of biomass derivatives to synthesize valuable chemicals and of other applications of metal oxides, such as depollution, photocatalysis, hydrogen production and fuel-cell components. The importance of metal oxide catalysis in environmental and green chemistry and sustainability is discussed, and challenges for the future are considered.

Selective Oxidation of 5-(Hydroxymethyl)furfural to DFF Using Water as Solvent and Oxygen as Oxidant with Earth-Crust-Abundant Mixed Oxides

5-Hydroxymethylfurfural (5-HMF) can be considered a prominent building block: because of the presence of the alcohol and aldehyde moieties, it can be used to generate useful molecules as chemicals of industrial interest with high added value, monomers for polymers, and even fuels. This article shows how building up mixed oxides of different complexities and properties may drive the selectivity toward one of the possible products generated from 5-HMF. In particular, mixed oxides based on cerium and other metals abundant on the earth-crust perform the selective oxidation of 5-HMF to 2,5-diformylfuran (94%), using oxygen as oxidant and water as solvent. The roles of the reaction conditions (temperature, reaction time, oxygen pressure, concentration of the substrate), the chemical composition, the acidic/basic properties, and redox properties of the catalysts are discussed.

Selective Oxidation of Veratryl Alcohol over Au-Pd/Ce0.62Zr0.38O₂ Catalysts Synthesized by Sol-Immobilization: Effect of Au:Pd Molar Ratio

The selective oxidation of veratryl alcohol (VA), a model compound of lignin, with oxygen molecules to produce veratraldehyde (VAld) was studied over monometallic Au, Pd, and bimetallic Au:Pd nanoparticles supported on a Ce_0.62Zr_0.38O₂ mixed oxide for the first time. These bimetallic Au-Pd catalysts with Au:Pd molar ratios from 0.4 to 4.3 were synthesized by the sol-immobilization method. Furthermore, all the catalysts were characterized by inductively coupled plasma-atomic emission spectroscopy (ICP-AES), N₂ physisorption, X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy-high angle annular dark field (STEM-HAADF) imaging, energy dispersive X-ray spectroscopy (EDXS), and temperature programmed reduction (TPR) techniques. A synergistic effect between gold and palladium was observed over all the bimetallic catalysts in a wide range of studied Au:Pd ratios. Remarkably, the optimum Au:Pd ratio for this reaction was 1.4 with a turnover frequency of almost six times larger than for the monometallic gold and palladium catalysts. Selectivity to veratraldehyde was higher than 99% for the monometallic Au, Pd, and all the bimetallic Au-Pd catalysts, and stayed constant during the reaction time.

Chemocatalytic Conversion of Cellulose into Key Platform Chemicals

Chemocatalytic transformation of lignocellulosic biomass to value-added chemicals has attracted global interest in order to build up sustainable societies. Cellulose, the first most abundant constituent of lignocellulosic biomass, has received extensive attention for its comprehensive utilization of resource, such as its catalytic conversion into high value-added chemicals and fuels (e.g., HMF, DMF, and isosorbide). However, the low reactivity of cellulose has prevented its use in chemical industry due to stable chemical structure and poor solubility in common solvents over the cellulose. Recently, homogeneous or heterogeneous catalysis for the conversion of cellulose has been expected to overcome this issue, because various types of pretreatment and homogeneous or heterogeneous catalysts can be designed and applied in a wide range of reaction conditions. In this review, we show the present situation and perspective of homogeneous or heterogeneous catalysis for the direct conversion of cellulose into useful platform chemicals.

Recent progress in homogeneous Lewis acid catalysts for the transformation of hemicellulose and cellulose into valuable chemicals, fuels, and nanocellulose

The evolution from petroleum-based products to the bio-based era by using renewable resources is one of the main research challenges in the coming years. Lignocellulosic biomass, consisting of inedible plant material, has emerged as a potential alternative for the production of biofuels, biochemicals, and nanocellulose-based advanced materials. The lignocellulosic biomass, which consists mainly of carbohydrate-based polysaccharides (hemicellulose and cellulose), is a green intermediate for the synthesis of bio-based products. In recent years, the re-engineering of biomass into a variety of commodity chemicals and liquid fuels by using Lewis acid catalysts has attracted much attention. Much research has been focused on developing new chemical strategies for the valorization of different biomass components. Homogeneous Lewis acid catalysts seem to be one of the most promising catalysts due to their astonishing features such as being less corrosive to equipment and being friendlier to the environment, as well as having the ability to disrupt the bonding system effectively and having high selectivity. Thus, these catalysts have emerged as important tools for the highly selective transformation of biomass components into valuable chemicals and fuels. This review provides an insightful overview of the most important recent developments in homogeneous Lewis acid catalysis toward the production and upgrading of biomass. The chemical valorization of the main components of lignocellulosic biomass (hemicellulose and cellulose), the reaction conditions, and process mechanisms are reviewed.

A high performance catalyst of shape-specific ruthenium nanoparticles for production of primary amines by reductive amination of carbonyl compounds

The creation of metal catalysts with highly active surfaces is pivotal to meeting the strong economic demand of the chemical industry. Specific flat-shaped pristine fcc ruthenium nanoparticles having a large fraction of atomically active {111} facets exposed on their flat surfaces have been developed that act as a highly selective and reusable heterogeneous catalyst for the production of various primary amines at exceedingly high reaction rates by the low temperature reductive amination of carbonyl compounds. The high performance of the catalyst is attributed to the large fraction of metallic Ru serving as active sites with weak electron donating ability that prevail on the surface exposed {111} facets of flat-shaped fcc Ru nanoparticles. This catalyst exhibits a highest turnover frequency (TOF) of ca. 1850 h-1 for a model reductive amination of biomass derived furfural to furfurylamine and provides a reaction rate approximately six times higher than that of an efficient and selective support catalyst of Ru-deposited Nb2O5 (TOF: ca. 310 h-1).

Electrobiorefineries: Unlocking the Synergy of Electrochemical and Microbial Conversions

An integrated biobased economy urges an alliance of the two realms of "chemical production" and "electric power". The concept of electrobiorefineries provides a blueprint for such an alliance. Joining the forces of microbial and electrochemical conversions in electrobiorefineries allows interfacing the production, storage, and exploitation of electricity as well as biobased chemicals. Electrobiorefineries are a technological evolution of biorefineries by the addition of (bio)electrochemical transformations. This interfacing of microbial and electrochemical conversions will result in synergies affecting the entire process line, like enlarging the product portfolio, increasing the productivity, or exploiting new feedstock. A special emphasis is given to the utilization of oxidative and reductive electroorganic reactions of microbially produced intermediates that may serve as privileged building blocks.

Electronic Effect of Ruthenium Nanoparticles on Efficient Reductive Amination of Carbonyl Compounds

Highly selective synthesis of primary amines over heterogeneous catalysts is still a challenge for the chemical industry. Ruthenium nanoparticles supported on Nb₂O₅ act as a highly selective and reusable heterogeneous catalyst for the low-temperature reductive amination of various carbonyl compounds that contain reduction-sensitive functional groups such as heterocycles and halogens with NH₃ and H₂ and prevent the formation of secondary amines and undesired hydrogenated byproducts. The selective catalysis of these materials is likely attributable to the weak electron-donating capability of Ru particles on the Nb₂O₅ surface. The combination of this catalyst and homogeneous Ru systems was used to synthesize 2,5-bis(aminomethyl)furan, a monomer for aramid production, from 5-(hydroxymethyl)furfural without a complex mixture of imine byproducts.

Heterogeneously-Catalyzed Aerobic Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid with MnO2

A simple non-precious-metal catalyst system based on costeffective and ubiquitously available MnO₂ , NaHCO₃ , and molecular oxygen was used to convert 5-hydroxymethylfurfural (HMF) to 2,5-difurandicarboxylic acid (FDCA) as a bioplastics precursor in 91 % yield. The MnO₂ catalyst could be recovered by simple filtration and reused several times. The present system was also applicable to the aerobic oxidation of other biomass-derived substrates and the gram-scale oxidation of HMF to FDCA, in which 2.36 g (86 % yield) of the analytically pure FDCA could be isolated.

MOF catalysts in biomass upgrading towards value-added fine chemicals

The development of new synthetic routes from biomass sources towards already existing molecules, which are then called bio-based molecules, or the transformation of biomass into new building blocks and materials will be of great impact. This review presents a critical comparison between MOFs and other catalysts (e.g. zeolites) for biomass transformation.

Hydrothermal synthesis of a layered-type W–Ti–O mixed metal oxide and its solid acid activity

A layered-type W–Ti–O mixed oxide was synthesized by hydrothermal synthesis from an aqueous solution of ammonium metatungstate and titanium sulfate.