Supporting Nano Catalysts for the Selective Hydrogenation of Biomass-derived Compounds

The selective hydrogenation of biomass derivatives presents a promising pathway for the production of high-value chemicals and fuels, thereby reducing reliance on traditional petrochemical industries. Recent strides in catalyst nanostructure engineering, achieved through tailored support properties, have significantly enhanced the hydrogenation performance in biomass upgrading. A comprehensive understanding of biomass selective upgrading reactions and the current advancement in supported catalysts is crucial for guiding future processes in renewable biomass. This review aims to summarize the development of supported nanocatalysts for the selective hydrogenation of the US DOE's biomass platform compounds derivatives into valuable upgraded molecules. The discussion includes an exploration of the reaction mechanisms and conditions in catalytic transfer hydrogenation (CTH) and high-pressure hydrogenation. By thoroughly examining the tailoring of supports, such as metal oxide catalysts and porous materials, in nano-supported catalysts, we elucidate the promoting role of nanostructure engineering in biomass hydrogenation. This endeavor seeks to establish a robust theoretical foundation for the fabrication of highly efficient catalysts. Furthermore, the review proposes prospects in the field of biomass utilization and address application bottlenecks and industrial challenges associated with the large-scale utilization of biomass.

Solar-Driven Photothermal Catalytic Lignocellulosic Biomass-to-H2 Conversion

The conversion of lignocellulosic biomass to chemical fuel can achieve the sustainable use of lignocellulosic biomass, but it was limited by the lack of an effective conversion strategy. Here, we reported a unique approach of photothermal catalysis by using MoS2-reduced graphene oxide (MoS2/RGO) as the catalyst to convert lignocellulosic biomass into H2 fuel in alkaline solution. The RGO acting as a support for the growth of MoS2 results in the high exposed Mo edges, which act as efficient Lewis acidic sites for the oxygenolysis of lignocellulosic biomass dissolved in alkaline solution. The broad light absorption capacity and abundant Lewis acidic sites make MoS2/RGO to be efficient catalysts for photothermal catalytic H2 production from lignocellulosic biomass, and the H2 generation rate with respect to catalyst under 300 W Xe lamp irradiation in cellulose, rice straw, wheat straw, polar wood chip, bamboo, rice hull, and corncob aqueous solution achieve 223, 168, 230, 564, 390, 234, and 55 μmol·h-1·g-1, respectively. It is believed that this photothermal catalysis is a simple and "green" approach for the lignocellulosic biomass-to-H2 conversion, which would have great potential as a promising approach for solar energy-driven H2 production from lignocellulosic biomass.

Direct Furfural Production from Deciduous Wood Pentosans Using Different Phosphorus-Containing Catalysts in the Context of Biorefining

This study seeks to improve the effectiveness of the pretreatment stage when direct furfural production is integrated into the concept of a lignocellulosic biomass biorefinery. First of all, the catalytic effects of different phosphorus-containing salts (AlPO₄, Ca₃(PO₄)₂, FePO₄, H₃PO₄, NaH₂PO₄) were analysed in hydrolysis for their ability to convert birch wood C-5 carbohydrates into furfural. The hydrolysis process was performed with three different amounts of catalyst (2, 3 and 4 wt.%) at a constant temperature (175 °C) and treatment time (90 min). It was found that the highest amount of furfural (63-72%, calculated based on the theoretically possible yield (% t.p.y.)) was obtained when H₃PO₄ was used as a catalyst. The best furfural yield among the used phosphorus-containing salts was obtained with NaH₂PO₄: 40 ± 2%. The greatest impact on cellulose degradation during the hydrolysis process was observed using H₃PO₄ at 12-20% of the initial amount, while the lowest degradation was observed using NaH₂PO₄ as a catalyst. The yield of furfural was 60.5-62.7% t.p.y. when H₃PO₄ and NaH₂PO₄ were combined (1:2, 1:1, or 2:1 at a catalyst amount of 3 wt.%); however, the amount of cellulose that was degraded did not exceed 5.2-0.3% of the starting amount. Enzymatic hydrolysis showed that such pretreated biomass could be directly used as a substrate to produce glucose. The highest conversion ratio of cellulose into glucose (83.1%) was obtained at an enzyme load of 1000 and treatment time of 48 h.

Enhanced Furfural Production in Deep Eutectic Solvents Comprising Alkali Metal Halides as Additives

The addition of alkali metal halide salts to acidic deep eutectic solvents is here reported as an effective way of boosting xylan conversion into furfural. These salts promote an increase in xylose dehydration due to the cation and anion interactions with the solvent being a promising alternative to the use of harsh operational conditions. Several alkali metal halides were used as additives in the DES composed of cholinium chloride and malic acid ([Ch]Cl:Mal) in a molar ratio of 1:3, with 5 wt.% of water. These mixtures were then used as both solvent and catalyst to produce furfural directly from xylan through microwave-assisted reactions. Preliminary assays were carried out at 150 and 130 °C to gauge the effect of the different salts in furfural yields. A Response Surface Methodology was then applied to optimize the operational conditions. After an optimization of the different operating conditions, a maximum furfural yield of 89.46 ± 0.33% was achieved using 8.19% of lithium bromide in [Ch]Cl:Mal, 1:3; 5 wt.% water, at 157.3 °C and 1.74 min of reaction time. The used deep eutectic solvent and salt were recovered and reused three times, with 79.7% yield in the third cycle, and the furfural and solvent integrity confirmed.

Upcycling polyamide containing post-consumer Tetra Pak carton packaging to valuable chemicals and recyclable polymer

Billion tons of post-consumer Tetra Pak cartons are discarded annually as land and ocean wastes, creating significant environmental problems and resource losses. Recycling of the carton wastes is hindered by its multi-material compositions and low values of the recycled products. In this study, a novel upcycling of the cartons was investigated. A post-consumer carton consisting of paper, polyolefin, and polyamide was directly converted in 210-230 °C tetrahydrofuran containing 10-20 mM acid to produce up to 19.2% of levoglucosenone and 8.6% of furfural by selectively decomposing paper fraction. The remaining solids containing mostly intact polyethylene and polyamide but also a smaller fraction of paper-derived char were separated using a solvent-dissolution method. The xylene-soluble fraction was a recycled polymer similar to the original polyethylene, which was verified by its functional groups, the composition of the pyrolysis products, and the melt rheology results. The xylene-insoluble fraction was a mixture of polyamide and paper-derived char. Upon pyrolysis, caprolactam was produced as the only major vapor product. The remaining, thermally stable paper-derived char could be used as a high-quality solid fuel. Overall, the demonstrated recycling method could potentially maximize the values of the products recovered from carton wastes.

Synthesis of amides and esters containing furan rings under microwave-assisted conditions

In this work, we present a novel method for the synthesis of ester and amide derivatives containing furan rings (furfural derivatives) under mild synthetic conditions supported by microwave radiation. N-(Furan-2-ylmethyl)furan-2-carboxamide and furan-2-ylmethyl furan-2-carboxylate were produced using 2-furoic acid, furfurylamine, and furfuryl alcohol. The reactions were carried out in a microwave reactor in the presence of effective coupling reagents: DMT/NMM/TsO− or EDC. The reaction time, the solvent, and the amounts of the substrates were optimized. After crystallization or flash chromatography, the final compounds were isolated with good or very good yields. Our method allows for the synthesis of N-blocked amides using N-blocked amino acids (Boc, Cbz, Fmoc) and amine. As well as compounds with a monoamide and ester moiety, products with diamides and diester bonds (N,N-bis(furan-2-ylmethyl)furan-2,5-dicarboxamide, bis(furan-2-ylmethyl) furan-2,5-dicarboxylate, and furan-3,4-diylbis(methylene) bis(furan-2-carboxylate)) were synthesized with moderate yields in the presence of DMT/NMM/TsO– or EDC, using 2,5-furandicarboxylic acid and 3,4-bis(hydroxymethyl)furan as substrates.

Cotton stalk-derived hydrothermal carbon for methylene blue dye removal: investigation of the raw material plant tissues

Conversion of the abundant agricultural residual cotton stalk (CS) into useful chemicals or functional materials could alleviate the fossil fuels caused energy shortages and environmental crises. Although some advances have been achieved, less attention has been paid to the plant tissues effect. In this study, the plant tissue of CS was changed by part degradation of some components (hemicelluloses and lignin, for example) with the aid of acid/base (or both). The pretreated CS was transformed into hydrochar by hydrothermal carbonization (HTC) method. Morphological and chemical compositions of CS hydrochar were analyzed by various techniques, including elemental analysis, Fourier transform infrared (FTIR), BET analysis, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). Methylene blue (MB) removal of prepared CS hydrochar was used to evaluate CS hydrochar pollutions adsorption capacity. Results reveal acid/base (or both) pretreatment is beneficial for CS raw material to prepare high-quality CS hydrochar. The effects of some parameters, such as initial MB concentration, temperature, pH value and recyclability on the adsorption of MB onto both acid and base-pretreated CS hydrochar (CS-H2SO4 + NaOH-HTC) were studied. The present work exhibits the importance of agricultural waste biomass material plant tissues on its derived materials, which will have a positive effect on the direct utilization of waste biomass.

New Approach to Dehydration of Xylose to 2-Furfuraldehyde Using a Mesoporous Niobium-Based Catalyst

Furfural chemistry is one of the most promising platforms directly derived from lignocellulose biomass. In this study, a niobium-based catalyst (mNb-bc) was synthesized by a new fast and simple method. This new method uses microemulsion to obtain a catalyst with a high specific surface area (340 m² g^-1), defined mesoporosity, and high acidity (65 μmol g^-1). Scanning electron microscopy revealed that mNb-bc has a rough surface. The mNb-bc was used to catalyze the conversion reaction of xylose into 2-furfuraldehyde in a monophasic system using water as a green solvent. This reaction was investigated using a 2³ experimental design by varying the temperature, time, and catalyst-to-xylose ratio (CXR). The responses evaluated were xylose conversion (X _c), reaction yield (Y), and selectivity to 2-furfuraldehyde (S). The optimized reaction conditions were used to evaluate the reaction kinetics. At milder reaction conditions of 140 °C, 2 h, and a CXR of 10%, mNb-bc led to an X _c value of 41.2%, an S value of 77.1%, and a Y value of 31.8%.

Optimization with Response Surface Methodology of Microwave-Assisted Conversion of Xylose to Furfural

The production of furfural from renewable sources, such as lignocellulosic biomass, has gained great interest within the concept of biorefineries. In lignocellulosic materials, xylose is the most abundant pentose, which forms the hemicellulosic part. One of the key steps in the production of furfural from biomass is the dehydration reaction of the pentoses. The objective of this work was to assess the conditions under which the concentration of furfural is maximized from a synthetic, monophasic, and homogeneous xylose medium. The experiments were carried out in a microwave reactor. FeCl3 in different proportions and sulfuric acid were used as catalysts. A two-level, three-factor experimental design was developed for this purpose. The results were further analyzed through a second experimental design and optimization was performed by response surface methodology. The best operational conditions for the highest furfural yield (57%) turned out to be 210 °C, 0.5 min, and 0.05 M FeCl3.

Continuous Flow Upgrading of Selected C2-C6 Platform Chemicals Derived from Biomass

The ever increasing industrial production of commodity and specialty chemicals inexorably depletes the finite primary fossil resources available on Earth. The forecast of population growth over the next 3 decades is a very strong incentive for the identification of alternative primary resources other than petro-based ones. In contrast with fossil resources, renewable biomass is a virtually inexhaustible reservoir of chemical building blocks. Shifting the current industrial paradigm from almost exclusively petro-based resources to alternative bio-based raw materials requires more than vibrant political messages; it requires a profound revision of the concepts and technologies on which industrial chemical processes rely. Only a small fraction of molecules extracted from biomass bears significant chemical and commercial potentials to be considered as ubiquitous chemical platforms upon which a new, bio-based industry can thrive. Owing to its inherent assets in terms of unique process experience, scalability, and reduced environmental footprint, flow chemistry arguably has a major role to play in this context. This review covers a selection of C₂ to C₆ bio-based chemical platforms with existing commercial markets including polyols (ethylene glycol, 1,2-propanediol, 1,3-propanediol, glycerol, 1,4-butanediol, xylitol, and sorbitol), furanoids (furfural and 5-hydroxymethylfurfural) and carboxylic acids (lactic acid, succinic acid, fumaric acid, malic acid, itaconic acid, and levulinic acid). The aim of this review is to illustrate the various aspects of upgrading bio-based platform molecules toward commodity or specialty chemicals using new process concepts that fall under the umbrella of continuous flow technology and that could change the future perspectives of biorefineries.

Continuous Hydrogenation of Aqueous Furfural Using a Metal-Supported Activated Carbon Monolith

Continuous hydrogenation of aqueous furfural (4.5%) was studied using a monolith form (ACM) of an activated carbon Pd catalyst (∼1.2% Pd). A sequential reaction pathway was observed, with ACM achieving high selectivity and space time yields (STYs) for furfuryl alcohol (∼25%, 60-70 g/L-cat/h, 7-15 1/h liquid hourly space velocity, LHSV), 2-methylfuran (∼25%, 45-50 g/L-cat/h, 7-15 1/h LHSV), and tetrahydrofurfuryl alcohol (∼20-60%, 10-50 g/L-cat/h, <7 1/h LHSV). ACM showed a low loss of activity and metal leaching over the course of the reactions and was not limited by H2 external mass transfer resistance. Acetic acid (1%) did not significantly affect furfural conversion and product yields using ACM, suggesting Pd/ACM's potential for conversion of crude furfural. Limited metal leaching combined with high metal dispersion and H2 mass transfer rates in the composite carbon catalyst (ACM) provides possible advantages over granular and powdered forms in continuous processing.