One-pot conversions of lignocellulosic and algal biomass into liquid fuels

Synthesis and Catalytic Applications of Advanced Sn- and Zr-Zeolites Materials

The incorporation of isolated Sn (IV) and Zr (IV) ions into silica frameworks is attracting widespread attention, which exhibits remarkable catalytic performance (conversion, selectivity, and stability) in a broad range of reactions, especially in the field of biomass catalytic conversion. As a representative example, the conversion route of carbohydrates into valuable platform and commodity chemicals such as lactic acid and alkyl lactates, has already been established. The zeotype materials also possess water-tolerant ability and are capable to be served as promising heterogeneous catalysts for aqueous reactions. Therefore, dozens of Sn- and Zr-containing silica materials with various channel systems have been prepared successfully in the past decades, containing 8 membered rings (MR) small pore CHA zeolite, 10-MR medium pore zeolites (FER, MCM-56, MEL, MFI, MWW), 12-MR large pore zeolites (Beta, BEC, FAU, MOR, MSE, MTW), and 14-MR extra-large pore UTL zeolite. This review about Sn- and Zr-containing metallosilicate materials focuses on their synthesis strategy, catalytic applications for diverse reactions, and the effect of zeolite characteristics on their catalytic performances.

Pyrrole Compounds from the Two-Step One-Pot Conversion of 2,5-Dimethylfuran for Elastomer Composites with Low Dissipation of Energy

A one-pot, two-step process was developed for the preparation of pyrrole compounds from 2,5-dimethylfuran. The first step was the acid-catalyzed ring-opening reaction of 2,5-dimethylfuran (DF), leading to the formation of 2,5-hexanedione (HD). A stoichiometric amount of water and a sub-stoichiometric amount of sulfuric acid were used by heating at 50 °C for 24 h. Chemically pure HD was isolated, with a quantitative yield (up to 95%), as revealed by 1H-NMR, 13C-NMR, and GC-MS analyses. In the second step, HD was used as the starting material for the synthesis of pyrrole compounds via the Paal-Knorr reaction. Various primary amines were used in stoichiometric amounts. 1H-NMR, 13C-NMR, ESI-Mass, and GC-Mass analyses confirmed that pyrrole compounds were prepared with very good/excellent yields (80-95%), with water as the only co-product. A further purification step was not necessary. The process was characterized by a very high carbon efficiency, up to 80%, and an E-factor down to 0.128, whereas the typical E-factor for fine chemicals is between 5 and 50. Water, a co-product of the second step, can trigger the first step and therefore make the whole process circular. Thus, this synthetic pathway appears to be in line with the requirements of a sustainable chemical process. A pyrrole compound bearing an SH group (SHP) was used for the functionalization of a furnace carbon black (CB). The functionalized CB (CB/SHP) was utilized in place of silica, resulting in a 15% mass reduction of reinforcing filler, in an elastomeric composite based on poly(styrene-co-butadiene) from solution anionic polymerization and poly(1,4-cis-isoprene) from Hevea Brasiliensis. Compared to the silica-based composite, a reduction in the Payne effect of about 25% and an increase in the dynamic rigidity (E' at 70 °C) of about 25% were obtained with CB/SHP.

Highly Effective Activated Carbon-Supported Ni-Mn Bifunctional Catalyst for Selective Hydrodeoxygenation of 5-Hydroxymethylfurfural to 2,5-Dimethylfuran

Designing highly efficient and low-cost catalysts for conversion of renewable biomass into high value-added chemicals and biofuels is important and challenging. Herein, a non-noble Ni-Mn bifunctional catalyst supported on activated carbon (Ni-Mn/AC) was developed by an incipient wetness impregnation method. The catalyst was found to be economic and efficient for the selective hydrodeoxygenation of biomass-derived 5-hydroxymethylfurfural (5-HMF) to 2,5-dimethylfuran (2,5-DMF). The optimal Ni-Mn/AC (Ni/Mn=3) catalyst achieved 98.5 % 2,5-DMF yield with 100 % conversion of 5-HMF under mild reaction conditions of 180 °C, 2.0 MPa H₂ for 4 h. Furthermore, the catalyst exhibited outstanding reusability and could be recycled eight times without loss of activity. The addition of Mn not only enhanced the reactivity of 5-HMF but also resulted in the dominant reaction pathway shift from the hydrogenation of the C=O bond to the hydrogenolysis of C-OH bond, which was attributed to the synergy of highly dispersed Ni metallic nanoparticles and moderate Lewis acid sites from MnO_x as revealed by detailed characterizations.

A Review on the Critical Role of H2 Donor in the Selective Hydrogenation of 5-Hydroxymethylfurfural

The selective hydrogenation of 5-hydroxymethylfurfural (HMF) has been of great interest to many scientists and researchers. However, conventional hydrogenation inevitably requires the use of gaseous hydrogen as a reducing agent, which is detrimental to its storage and transport. In this regard, other economical and environmentally friendly strategies, such as catalytic transfer hydrogenation/hydrogenolysis without external molecular H₂ , become more and more attractive. This Review provides the status and insight into the current research of hydrogenating HMF to high-value chemicals, using formic acid, alcohols, polymethylhydrosiloxane, water, and sodium borohydride as hydrogen donors and explains the hydrogenation mechanisms and the related hydrogenation characteristics of different hydrogen donors in the catalytic systems.

Catalytic Upgrading of Lignocellulosic Biomass Sugars Toward Biofuel 5-Ethoxymethylfurfural

The conversion of biomass into high-value chemicals through biorefineries is a requirement for sustainable development. Lignocellulosic biomass (LCB) contains polysaccharides and aromatic polymers and is one of the important raw materials for biorefineries. Hexose and pentose sugars can be obtained from LCB by effective pretreatment methods, and further converted into high-value chemicals and biofuels, such as 5-hydroxymethylfurfural (HMF), levulinic acid (LA), γ-valerolactone (GVL), ethyl levulinate (EL), and 5-ethoxymethylfurfural (EMF). Among these biofuels, EMF has a high cetane number and superior oxidation stability. This mini-review summarizes the mechanism of several important processes of EMF production from LCB-derived sugars and the research progress of acid catalysts used in this reaction in recent years. The influence of the properties and structures of mono- and bi-functional acid catalysts on the selectivity of EMF from glucose were discussed, and the effect of reaction conditions on the yield of EMF was also introduced.

Development of Sustainable Catalytic Pathways for Furan Derivatives

Biomass, the only globally available, renewable feedstock of organic carbon, is considered a viable alternative to fossil fuels. It can be efficiently utilized to produce various building blocks in accordance with green and sustainable chemistry principles. In this review, recent progress, such as the transformation of carbohydrates (C5 or C6 sugar, inulin, and cellulose) and their derivatives (furfural, hydroxymethylfurfural) into significant platform chemicals over polyoxometalates, zeolites, non-noble metals, and ionic liquids in single or multiphase, is evaluated.

Insight into Biomass Upgrade: A Review on Hydrogenation of 5-Hydroxymethylfurfural (HMF) to 2,5-Dimethylfuran (DMF)

Recent developments in the transformation of biobased 5-hydroxymethylfurfural (HMF) into a potential liquid fuel, 2,5-dimethylfuran (DMF), are summarised. This review focuses briefly on the history of HMF conversion to DMF in terms of the feedstock used and emphasises the ideal requirements in terms of the catalytic properties needed in HMF transformation into DMF. The recent state of the art and works on HMF transformation into DMF are discussed in comparison to noble metals and non-noble metals as well as bimetallic catalysts. The effect of the support used and the reaction conditions are also discussed. The recommendations for future work and challenges faced are specified.

Membrane Purification Techniques for Recovery of Succinic Acid Obtained from Fermentation Broth during Bioconversion of Lignocellulosic Biomass: Current Advances and Future Perspectives

Recently, the bioconversion of biomass into biofuels and biocommodities has received significant attention. Although green technologies for biofuel and biocommodity production are advancing, the productivity and yield from these techniques are low. Over the past years, various recovery and purification techniques have been developed and successfully employed to improve these technologies. However, these technologies still require improvement regarding the energy-consumption-related costs, low yield and product purity. In the context of sustainable green production, this review presents a broad review of membrane purification technologies/methods for succinic acid, a biocommodity obtained from lignocellulosic biomass. In addition, a short overview of the global market for sustainable green chemistry and circular economy systems or zero waste approach towards a sustainable waste management is presented. Succinic acid, the available feedstocks for its production and its industrial applications are also highlighted. Downstream separation processes of succinic acid and the current studies on different downstream processing techniques are critically reviewed. Furthermore, critical analysis of membrane-based downstream processes of succinic acid production from fermentation broth is highlighted. A short review of the integrated-membrane-based process is discussed, as well, because integrating “one-pot” lignocellulosic bioconversion to succinic acid with downstream separation processing is considered a critical issue to address. In conclusion, speculations on outlook are suggested.

A state-of-the-art review on emission characteristics of SI and CI engines fueled with 2,5-dimethylfuran biofuel

Currently, the considerable decline in fossil fuel resources and the high rise in vehicle emissions have prompted researchers and governments to formulate strategies for sustainable energy development. In addition to imposing strict laws, promoting sustainable energy sources such as the development of new types of non-fossil fuels has been considered a suitable direction for the roadmap to healing the Earth's environment. Biomass sources have affirmed huge potentials in the production of biofuels. In the pathway of searching renewable biofuels, it is found that that 2,5-dimethylfuran (DMF) can become a promising fuel because it is synthesized from lignocellulose biomass, which is an available feedstock for the production of prospective fuels. Indeed, recent review studies have focused in great detail on engine performance evaluation using DMF but seemed to have gaps in emission characteristics. In this work, the controversial issues of emissions from spark and compression ignition engines during the DMF combustion were completely assessed. Indeed, the mechanism of formation and oxidation of DMF compounds during combustion was clearly described to serve as the basis for analyzing and comparing the pollution emission behavior of different fuels. More importantly, gaseous emissions, PM characteristics, and soot tendency from spark and compression ignition engines were thoroughly evaluated on the basis of the experimental and numerical data. In general, DMF has shown outstanding advantages upon emissions compared to fossil fuels; however, the impacts of DMF on the engine durability and fuel system should be further investigated to have a comprehensive analysis of this biofuel class.

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.

Recent progress in the development of advanced biofuel 5-ethoxymethylfurfural

Biomass-derived 5-ethoxymethylfurfural (EMF) with excellent energy density and satisfactory combustion performance holds great promise to meet the growing demands for transportation fuels and fuel additives to a certain extent. In this review, we summarized the relative merits of the EMF preparation from different feedstocks, such as platform chemicals, biomass sugars and lignocellulosic biomass. Advances for EMF synthesis over homogeneous (i.e. inorganic acids and soluble metal salts), heterogeneous catalysts (i.e. zeolites, heteropolyacid-based hybrids, sulfonic acid-functionalized catalysts, and others) or mixed-acid catalysts were performed as well. Additionally, the emerging development for the EMF production was also evaluated in terms of the different solvents system (i.e. single-phase solvents, biphasic solvents, ionic liquids, and deep eutectic solvents). It is concluded with current challenges and prospects for advanced biofuel EMF preparation in the future.

Upgrading of Carbohydrates to the Biofuel Candidate 5-Ethoxymethylfurfural (EMF)

5-Ethoxymethylfurfural (EMF), one of the significant platform molecular derivatives, is regarded as a promising biofuel and additive for diesel, owing to its high energy density (8.7 kWh·L−1). Several catalytic materials have been developed for the synthesis of EMF derived from different feedstocks under relatively mild reaction conditions. Although a great quantity of research has been conducted over the past decades, the unsatisfactory production selectivity mostly limited to the range 50%–70%, and the classic fructose used as the substrate restricted its application for fuel manufacture in large scale. To address these production improvements, this review pays attention to evaluate the activity of various catalysts (e.g., mineral salts, zeolites, heteropolyacid-based hybrids, sulfonic acid-functionalized materials, and ionic liquids), providing potential research directions for the design of novel catalysts for the achievement of further improved EMF yields.

Synthesis of Ethyl-4-ethoxy Pentanoate by Reductive Etherification of Ethyl Levulinate in Ethanol on Pd/SiO2 -C Catalysts

The synthesis of biomass-derived ethers to be used as biofuels or biofuel additives has attracted much attention. Following the recently reported synthesis of etherified ester ethyl-4-ethoxy pentanoate (EEP) from γ-valerolactone (GVL) in ethanol catalyzed by H-beta zeolite, an alternative route to prepare EEP in high yield has been developed by reductive etherification of ethyl levulinate (EL) in ethanol at 140 °C under 0.5 MPa H₂ with a silica-modified Pd/C catalyst. The ether production likely follows a tandem acetalization-hydrogenolysis process with ethyl-4,4-diethoxy pentanoate (EDEP) as the intermediate. The acetalization step can be favored by introducing acidic materials, such as SiO₂ -carbon or beta zeolite, as a cocatalyst. The combination of the Pd/SiO₂ -C and beta zeolite mixture leads to 100 % EL conversion and 93 % EEP selectivity under optimized reaction conditions. For the first time, the standard molar combustion enthalpy of as-prepared EEP is measured by using a static oxygen bomb, and the value of which is determined to be about -5658 kJ mol^-1 , which is much larger than that of GVL (-2650 kJ mol^-1 ).

Electrocatalytic Upgrading of Biomass-Derived Intermediate Compounds to Value-Added Products

The continuous advance in exploring renewable energy resources such as solar and wind will certainly alleviate our reliance on limited fossil reserves. However, the sustainable development of mankind demands not only energy but also carbon-based chemical goods. Unfortunately, exploitation of renewable energy resources like solar and wind will not lead to any carbon-based chemicals. The only sustainable and green carbon source is biomass, the scale of annual production of which has an immense potential to complement that of fossil-derived carbons. To utilize biomass in economically effective ways, many catalytic processes have been investigated. Among various strategies of biomass refinery, electrocatalytic upgrading stands out as an attractive option because of its benign operation conditions, high energy efficiency, and convenient control on production rate and selectivity using electrochemical parameters. This Minireview showcases several electrocatalytic systems for both reductive and oxidative upgrading of representative biomass-derived intermediate compounds, including 5-hydroxymethylfurfural, furfural, levulinic acid, glycerol, and sorbitol to different value-added products. The catalytic routes and mechanisms of each biomass-derived platform compound are discussed and compared. In order to be feasible for large-scale applications, low-cost composition and preparation of electrocatalysts are mandatory and will be emphasized. Finally, our personal perspective on the current challenges and future directions of electrocatalytic biomass upgrading is presented.

How Catalysts and Experimental Conditions Determine the Selective Hydroconversion of Furfural and 5-Hydroxymethylfurfural

Furfural and 5-hydroxymethylfurfural stand out as bridges connecting biomass raw materials to the biorefinery industry. Their reductive transformations by hydroconversion are key routes toward a wide variety of chemicals and biofuels, and heterogeneous catalysis plays a central role in these reactions. The catalyst efficiency highly depends on the nature of metals, supports, and additives, on the catalyst preparation procedure, and obviously on reaction conditions to which catalyst and reactants are exposed: solvent, pressure, and temperature. The present review focuses on the roles played by the catalyst at the molecular level in the hydroconversion of furfural and 5-hydroxymethylfurfural in the gas or liquid phases, including catalytic hydrogen transfer routes and electro/photoreduction, into oxygenates or hydrocarbons (e.g., furfuryl alcohol, 2,5-bis(hydroxymethyl)furan, cyclopentanone, 1,5-pentanediol, 2-methylfuran, 2,5-dimethylfuran, furan, furfuryl ethers, etc.). The mechanism of adsorption of the reactant and the mechanism of the reaction of hydroconversion are correlated to the specificities of each active metal, both noble (Pt, Pd, Ru, Au, Rh, and Ir) and non-noble (Ni, Cu, Co, Mo, and Fe), with an emphasis on the role of the support and of additives on catalytic performances (conversion, yield, and stability). The reusability of catalytic systems (deactivation mechanism, protection, and regeneration methods) is also discussed.

Selective Hydrodeoxygenation of 5-Hydroxymethylfurfural to 2,5-Dimethylfuran over Heterogeneous Iron Catalysts

This work provided the first example of selective hydrodeoxygenation of 5-hydroxymethylfurfural (HMF) to 2,5-dimethylfuran (DMF) over heterogeneous Fe catalysts. A catalyst prepared by the pyrolysis of an Fe-phenanthroline complex on activated carbon at 800 °C was demonstrated to be the most active heterogeneous Fe catalyst. Under the optimal reaction conditions, complete conversion of HMF was achieved with 86.2 % selectivity to DMF. The reaction pathway was investigated thoroughly, and the hydrogenation of the C=O bond in HMF was demonstrated to be the rate-determining step during the hydrodeoxygenation, which could be accelerated greatly by using alcohol solvents as additional H-donors. The excellent stability of the Fe catalyst, which was probably a result of the well-preserved active species and the pore structure of the Fe catalyst in the presence of H₂ , was demonstrated in batch and continuous flow fixed-bed reactors.

Efficient utilization of potash alum as a green catalyst for production of furfural, 5-hydroxymethylfurfural and levulinic acid from mono-sugars

Potash alum (PA) as an inexpensive, efficient and green catalyst for production of high value platform chemicals such as 5-hydroxymethylfurfural (HMF), levulinic acid and furfural from bio-renewable feedstocks, have been explored.

One-Pot Conversion of Carbohydrates into Furan Derivatives via Furfural and 5-Hydroxylmethylfurfural as Intermediates

Recently, there has been growing interest in the transformation of renewable biomass into value-added fuels and chemicals. The catalytic conversion of naturally abundant carbohydrates can generate two-important furan chemicals: 5-hydroxymethylfurfural (HMF) from C6 carbohydrates and furfural from C5 carbohydrates. Both HMF and furfural have received great interest as precursors in the synthesis of commodity chemicals and liquid fuels. In recent years, a trend has emerged to integrate sequential catalytic processes involving multistep reactions for the direct one-pot transformation of carbohydrates into the aimed fuels and chemicals. One-pot reactions have remarkably unique and environmentally friendly benefits, including the fact that isolation and purification of intermediate compounds can be avoided. Herein, the present article aims to review recent advances in the one-pot conversion of carbohydrates into furan derivatives via furfural and HMF as intermediates. Special attention will be paid to the catalytic systems, mechanistic insight, reaction pathways, and catalyst stability. It is expected that this review will guide researchers to develop effective catalytic systems for the one-pot transformation of carbohydrates into furan derivatives.

Electrocatalytic Hydrogenation of Oxygenates using Earth-Abundant Transition-Metal Nanoparticles under Mild Conditions

Electrocatalytic hydrogenation (ECH) is a sustainable pathway for the synthesis of value-added organic compounds, provided affordable catalysts with high activity, selectivity and durability are developed. Here, we synthesize Cu/C, Ni/C, and CuNi/C nanoparticles and compare their performance to Pt/C, Ru/C, PtRu/C for the ECH of hydroxyacetone, a bio-derived feedstock surrogate containing a carbonyl and a hydroxyl functional group. The non-precious metal electrocatalysts show promising conversion-time behavior, product selectivities, and Faradaic efficiencies. Ni/C forms propylene glycol with a selectivity of 89 % (at 80 % conversion), while Cu/C catalyzes ECH (52 % selectivity) and hydrodeoxygenation (HDO, 48 % selectivity, accounting for evaporation). CuNi/C shows increased turnover frequencies but reduced ECH selectivity (80 % at 80 % conversion) as compared to the Ni/C catalyst. Importantly, stability studies show that the non-precious metal catalysts do not leach at operating conditions.

Far infrared radiated energy-proficient rapid one-pot green hydrolysis of waste watermelon peel: optimization and heterogeneous kinetics of glucose synthesis

Energy-efficient far-infrared radiation rendered significant intensification of one-pot heterogeneous catalytic hydrolysis of waste watermelon peel for green synthesis of glucose.

One-pot production of 2,5-dimethylfuran from fructose over Ru/C and a Lewis–Brønsted acid mixture in N,N-dimethylformamide

A one-pot process for the production of 2,5-dimethylfuran from fructose by using Ru/C and a Lewis–Brønsted acid mixture as catalysts.

Catalytic Upgrading of 5-Hydroxymethylfurfural to Drop-in Biofuels by Solid Base and Bifunctional Metal-Acid Catalysts

Design and synthesis of effective heterogeneous catalysts for the conversion of biomass intermediates into long chain hydrocarbon precursors and their subsequent deoxygenation to hydrocarbons is a viable strategy for upgrading lignocellulose into distillate range drop-in biofuels. Herein, we report a two-step process for upgrading 5-hydroxymethylfurfural (HMF) to C9 and C11 fuels with high yield and selectivity. The first step involves aldol condensation of HMF and acetone with a water tolerant solid base catalyst, zirconium carbonate (Zr(CO3 )x ), which gave 92 % C9 -aldol product with high selectivity at nearly 100 % HMF conversion. The as-synthesised Zr(CO3 )x was analysed by several analytical methods for elucidating its structural properties. Recyclability studies of Zr(CO3 )x revealed a negligible loss of its activity after five consecutive cycles over 120 h of operation. Isolated aldol product from the first step was hydrodeoxygenated with a bifunctional Pd/Zeolite-β catalyst in ethanol, which showed quantitative conversion of the aldol product to n-nonane and 1-ethoxynonane with 40 and 56 % selectivity, respectively. 1-Ethoxynonane, a low oxygenate diesel range fuel, which we report for the first time in this paper, is believed to form through etherification of the hydroxymethyl group of the aldol product with ethanol followed by opening of the furan ring and hydrodeoxygenation of the ether intermediate.

Effects of Water on the Copper-Catalyzed Conversion of Hydroxymethylfurfural in Tetrahydrofuran

Reaction kinetics were studied to quantify the effects of water on the conversion of hydroxymethylfurfural (HMF) in THF over Cu/γ-Al2 O3 at 448 K using molecular H2 as the hydrogen source. We show that low concentrations of water (5 wt %) in the THF solvent significantly alter reaction rates and selectivities for the formation of reaction products by hydrogenation and hydrogenolysis processes. In the absence of water, HMF was converted primarily to hydrogenolysis products 2-methyl-5-hydroxymethylfuran (MHMF) and 2,5-dimethylfuran (DMF), whereas reactions carried out in THF-H2 O mixtures (THF/H2 O=95:5 w/w) led to the selective production of the hydrogenation product 2,5-bis(hydroxymethyl)furan (BHMF) and inhibition of HMF hydrogenolysis.

Current technologies, economics, and perspectives for 2,5-dimethylfuran production from biomass-derived intermediates

Since the U.S. Department of Energy (DOE) published a perspective article that described the potential of the top ten biomass-derived platform chemicals as petroleum replacements for high-value commodity and specialty chemicals, researchers around the world have been motivated to develop technologies for the conversion of biomass and biomass-derived intermediates into chemicals and fuels. Among several biorefinery processes, the conversion of biomass carbohydrates into 2,5-dimethylfuran (DMF) has received significant attention because of its low oxygen content, high energy content, and high octane value. DMF can further serve as a petroleum-replacement, biorenewable feedstock for the production of p-xylene (pX). In this review, we aim specifically to present a concise and up-to-date analysis of DMF production technologies with a critical discussion on catalytic systems, mechanistic insight, and process economics, which includes sensitivity analysis, so that more effective catalysts can be designed. Special emphasis has been given to bifunctional catalysts that improve DMF yields and selectivity and the synergistic effect of the bifunctional sites. Process economics for the current processes and the scope for further improvement are discussed. It is anticipated that the chemistry detailed in this review will guide researchers to develop more practical catalytic processes to enable the economic production of bio-based DMF. Processes for the upgrade of DMF to pX are also described.

Acidic ionic liquids as sustainable approach of cellulose and lignocellulosic biomass conversion without additional catalysts

The use of ionic liquids (ILs) for biomass processing has attracted considerable attention recently as it provides distinct features for pre-treated biomass and fractionated materials in comparison to conventional processes. Process intensification through integration of dissolution, fractionation, hydrolysis and/or conversion in one pot should be accomplished to maximise economic and technological feasibility. The possibility of using alternative ILs capable not only of dissolving and deconstructing selectively biomass but also of catalysing reactions simultaneously are a potential solution of this problem. In this Review a critical overview of the state of the art and perspectives of the hydrolysis and conversion of cellulose and lignocellulosic biomass using acidic ILs using no additional catalyst are provided. The efficiency of the process is mainly considered with regard to the hydrolysis and conversion yields obtained and the selectivity of each reaction. The process conditions can be easily tuned to obtain sugars and/or platform chemicals, such as furans and organic acids. On the other hand, product recovery from the IL and its purity are the main challenges for the acceptance of this technology as a feasible alternative to conventional processes.

Hydrodeoxygenation processes: advances on catalytic transformations of biomass-derived platform chemicals into hydrocarbon fuels

Lignocellulosic biomass provides an attractive source of renewable carbon that can be sustainably converted into chemicals and fuels. Hydrodeoxygenation (HDO) processes have recently received considerable attention to upgrade biomass-derived feedstocks into liquid transportation fuels. The selection and design of HDO catalysts plays an important role to determine the success of the process. This review has been aimed to emphasize recent developments on HDO catalysts in effective transformations of biomass-derived platform molecules into hydrocarbon fuels with reduced oxygen content and improved H/C ratios. Liquid hydrocarbon fuels can be obtained by combining oxygen removal processes (e.g. dehydration, hydrogenation, hydrogenolysis, decarbonylation etc.) as well as by increasing the molecular weight via C-C coupling reactions (e.g. aldol condensation, ketonization, oligomerization, hydroxyalkylation etc.). Fundamentals and mechanistic aspects of the use of HDO catalysts in deoxygenation reactions will also be discussed.

Renewable fuels from biomass-derived compounds: Ru-containing hydrotalcites as catalysts for conversion of HMF to 2,5-dimethylfuran

Ruthenium nanoparticle-containing hydrotalcite catalysts work efficiently for the conversion of biomass-derived HMF into liquid fuel 2,5-dimethylfuran.

Zinc-assisted hydrodeoxygenation of biomass-derived 5-hydroxymethylfurfural to 2,5-dimethylfuran

2,5-Dimethylfuran (DMF), a promising cellulosic biofuel candidate from biomass derived intermediates, has received significant attention because of its low oxygen content, high energy density, and high octane value. A bimetallic catalyst combination containing a Lewis-acidic Zn(II) and Pd/C components is effective for 5-hydroxymethylfurfural (HMF) hydrodeoxygenation (HDO) to DMF with high conversion (99%) and selectivity (85% DMF). Control experiments for evaluating the roles of zinc and palladium revealed that ZnCl2 alone did not catalyze the reaction, whereas Pd/C produced 60% less DMF than the combination of both metals. The presence of Lewis acidic component (Zn) was also found to be beneficial for HMF HDO with Ru/C catalyst, but the synergistic effect between the two metal components is more pronounced for the Pd/Zn system than the Ru/Zn. A comparative analysis of the Pd/Zn/C catalyst to previously reported catalytic systems show that the Pd/Zn system containing at least four times less precious metal than the reported catalysts gives comparable or better DMF yields. The catalyst shows excellent recyclability up to 4 cycles, followed by a deactivation, which could be due to coke formation on the catalyst surface. The effectiveness of this combined bimetallic catalyst has also been tested for one-pot conversion of fructose to DMF.