d -Glucose hydrogenation/hydrogenolysis reactions on noble metal (Ru, Pt)/activated carbon supported catalysts

Isolation of Highly Crystalline Cellulose via Combined Pretreatment/Fractionation and Extraction Procedures within a Biorefinery Concept

Sustainable production of bio-based materials and chemicals requires integrated approaches which utilize all fractions of lignocellulosic biomass. In this work, highly crystalline cellulose was isolated via combined pretreatment/fractionation and extraction processes from beechwood sawdust. The proposed approach was based on the selective recovery of hemicellulose components in the first step, followed by enhanced delignification in the second step, permitting the efficient recovery of the remaining cellulose via bleaching in the final step. Hydrothermal pretreatment under tailored conditions in neat water or dilute acid resulted in almost complete hemicellulose removal (80-96 wt %) in the liquid fraction. In the second step, the formed surface lignin was isolated via mild extraction while enhanced removal of both native/structural and surface lignin (71 wt %) was achieved by applying the organosolv treatment using dilute sulfuric acid as catalyst. Dilute sulfuric acid pretreatment followed by acid catalyzed organosolv pretreatment proved to be the most efficient combined approach, leading to 80 wt % hemicellulose removal as xylose monomer, and 71 wt % delignification. High crystallinity cellulose (<88%), with an overall cellulose recovery of 68-91 wt % based on native cellulose in parent biomass was isolated in the last step via bleaching of all pretreated biomass solids. The proposed integrated biorefinery procedures that aim to whole "waste" biomass valorization, replacing fossil resources, with the use of green solvents (water, ethanol) at relatively mild temperature/pressure conditions, are in line with the scope of several United Nations Sustainable Development Goals, such as UN SDG 8, 11, 12, and 13.

Facile Hydrogenolysis of Sugars to 1,2-Glycols by Ru@PPh3/OPPh3 Confined Large-Pore Mesoporous Silica

Tandem hydrogenation vis-à-vis hydrogenolysis of xylose to 1,2-glycols remains a major challenge. Although one-pot conversion of xylose to 1,2-glycols requires stringent conditions, a sustainable approach would be quite noteworthy. We have developed a microwave route for the one-pot conversion of pentose (C5) and hexose (C6) sugars into glycol and hexitol, without pressurized hydrogen reactors. A pronounced hydrogenolysis of sugars to glycols is observed by Ru single atom (SA) on triphenylphosphine/phosphine oxide-modified silica (Ru@SiP), in contrast to Ru SA on pristine (Ru@SiC) and 3-aminopropyl-modified silica (Ru@SiN). A promising "ligand effect" was observed through phosphine modification of silica that presents a 70% overall yield of all reduced sugars (xylitol + glycols) from a 99% conversion of xylose with Ru@SiP. A theoretical study by DFT depicts an electronic effect on Ru-SA by triphenylphosphine that promotes the catalytic hydrogenolysis of sugars under mild conditions. Hence, this research represents an important step for glycols from biomass-derived sources.

Production of Sorbitol via Hydrogenation of Glucose over Ruthenium Coordinated with Amino Styrene-co-maleic Anhydride Polymer Encapsulated on Activated Carbon (Ru/ASMA@AC) Catalyst

Sorbitol, a product primarily derived from glucose hydrogenation, has extensive applications in the pharmaceutical, chemical and other industries. Amino styrene-co-maleic anhydride polymer encapsulated on activated carbon (Ru/ASMA@AC) catalysts were developed for efficient glucose hydrogenation and were prepared and confined Ru by coordination with styrene-co-maleic anhydride polymer (ASMA). Through single-factor experiments, optimal conditions were determined to be 2.5 wt.% ruthenium loading and a catalyst usage of 1.5 g, 20% glucose solution at 130 °C, reaction pressure of 4.0 MPa, and a stirring speed of 600 rpm for 3 h. These conditions achieved a high glucose conversion rate of 99.68% and a sorbitol selectivity of 93.04%. Reaction kinetics testing proved that the hydrogenation of glucose catalyzed by Ru/ASMA@AC was a first-order reaction, with a reaction activation energy of 73.04 kJ/mol. Furthermore, the catalytic performance of the Ru/ASMA@AC and Ru/AC catalysts for glucose hydrogenation were compared and characterized by various detection methods. The Ru/ASMA@AC catalyst exhibited excellent stability after five cycles, whereas the traditional Ru/AC catalyst suffered from a 10% decrease in sorbitol yield after three cycles. These results suggest that the Ru/ASMA@AC catalyst is a more promising candidate for high-concentration glucose hydrogenation due to its high catalytic performance and superior stability.

Design of highly active Ni catalysts supported on carbon nanofibers for the hydrolytic hydrogenation of cellobiose

The direct transformation of cellulose into sugar alcohols (one-pot conversion) over supported nickel catalysts represents an attractive chemical route for biomass valorization, allowing the use of subcritical water in the hydrolysis step. The effectiveness of this process is substantially conditioned by the hydrogenation ability of the catalyst, determined by design parameters such as the active phase loading and particle size. Herein, mechanistic insights into catalyst design to produce superior activity were outlined using the hydrolytic hydrogenation of cellobiose as a model reaction. Variations in the impregnation technique (precipitation in basic media, incipient wetness impregnation, and the use of colloidal-deposition approaches) endowed carbon-nanofiber-supported catalysts within a wide range of Ni crystal sizes (5.8–20.4 nm) and loadings (5–14 wt%). The link between the properties of these catalysts and their reactivity has been established using characterization techniques such as X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and inductively coupled plasma-optical emission spectroscopy (ICP-OES). A fair compromise was found between the Ni surface area (3.89 m²/g) and its resistance against oxidation for intermediate crystallite sizes (∼11.3 nm) loaded at 10.7 wt%, affording the hydrogenation of 81.2% cellobiose to sorbitol after 3 h reaction at 190°C and 4.0 MPa H₂ (measured at room temperature). The facile oxidation of smaller Ni particle sizes impeded the use of highly dispersed catalysts to reduce the metal content requirements.

Recent Advances in C5 and C6 Sugar Alcohol Synthesis by Hydrogenation of Monosaccharides and Cellulose Hydrolytic Hydrogenation over Non-Noble Metal Catalysts

A new reality of the 21st century is the transition to a new type of economy and energy concepts characterized by the replacement of existing petrochemical routes to a bio-based circular economy. The needs for new strategies in obtaining basic products from bio-based resources with minimum CO₂ traces has become mandatory. In this review, recent trends in the conversion of biomass-derived molecules, such as simple monomeric sugars and cellulose, to industrially important C₅ and C₆ sugar alcohols on heterogeneous catalysts based on non-noble metals are discussed focusing on the influence of catalyst structures and reaction conditions used on the substrate conversion and product selectivity. The challenges and prominent ideas are suggested for the further development of catalytic hydrogenation of naturally abundant carbohydrates to value-added chemicals on non-noble metal catalysts.

Efficient Sorbitol Producing Process through Glucose Hydrogenation Catalyzed by Ru Supported Amino Poly (Styrene-co-Maleic) Polymer (ASMA) Encapsulated on γ-Al2O3

In this work, a core-shell-like sphere ruthenium catalyst, named as 5%Ru/γ-Al2O3@ASMA, has been successfully synthesized through impregnating the ruthenium nanoparticles (NPs) on the surface of the amino poly (styrene-co-maleic) polymer (ASMA) encapsulating γ-Al2O3 pellet support. The interaction between the Ru cations and the electro-donating polymer shell rich in hydroxyl and amino groups through the coordination bond would guarantee that the Ru NPs can be highly dispersed and firmly embedded on the surface of the support. In addition, the solid sphere γ-Al2O3 pellet could serve as the core to support the resulted catalysts applied in the flow process in a trickle bed reactor to promote the productivity. The resulted catalyst 5%Ru/γ-Al2O3@ASMA can be applied efficiently in the glucose hydrogenation and presents a steadfast sorbitol yield of almost 90% both in batch reactor and the trickle bed reactor, indicating the potential feasibility of the core-shell-like catalyst in the efficient production of sorbitol.

Highly Efficient and Recyclable Catalysts for Cellobiose Hydrolysis: Systematic Comparison of Carbon Nanomaterials Functionalized With Benzyl Sulfonic Acids

Carbon materials such as activated coal, nanotubes, nanofibers, or graphene nanoplatelets were functionalized with sulfonic acid moieties by a diazonium coupling strategy. High acidity was obtained for the majority of the carbon solids except for the carbon nanofibers. The activity of these acidic catalysts for the hydrolysis of cellobiose, as model molecule for cellulose, into glucose in neutral water medium was studied. The conversion of cellobiose is increasing with the acidity of the catalyst. We found that a minimum threshold amount of acidic functions is required for triggering the hydrolysis. The selectivity toward glucose is very high as soon as sulfonic functions are present on the catalyst. The robustness of the sulfonic functions grafted on the carbons has been highlighted by successful recyclability over six runs.

Efficient thermal- and photocatalysts made of Au nanoparticles on MgAl-layered double hydroxides for energy and environmental applications

Composites of the noble metal Au supported on MgAl-LDHs were prepared by a simple impregnation-reduction method to be used as thermal- and photocatalysts for the photocatalytic degradation of ciprofloxacin and thermocatalytic decomposition of formic acid to produce hydrogen. A collection of techniques, including X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) were employed to determine the structure and morphology properties of the as-prepared Au/MgAl-LDHs. The presence of surface Au(0) in Au/MgAl-LDHs was confirmed by TEM and XPS analyses. For the first time, we compared the effect of the surfactant PVP on the catalyst and found that the Au/MgAl-LDH composite with Au particle size of 2-8 nm had better catalytic activity than the (PVP@Au)/MgAl-LDH composite with Au particle size in the range of 1-5 nm. The sizes of Au NPs in the two catalysts were similar but had different effects on the catalytic performance. This indicated that the addition of PVP had an inhibitory effect on the catalytic activity of the catalyst. To evaluate the photostability of Au/MgAl-LDHs, recycle experiments for the photocatalytic degradation of ciprofloxacin were performed, and it was found that Au/MgAl-LDHs had good stability. Finally, we also applied Au/MgAl-LDHs in environmental catalysis and energy catalysis; we hope that they will be useful in practical applications.

Exploiting the Synergetic Behavior of PtPd Bimetallic Catalysts in the Selective Hydrogenation of Glucose and Furfural

Mono and bimetallic catalysts based on Pt and Pd were prepared by a co-precipitation method. They were tested in liquid phase hydrogenation reactions of glucose and furfural at low temperature and pressure. The bimetallic PtPd/TiO2 catalyst proved to be an efficient material in selectively hydrogenating glucose to sorbitol. Moreover, high furfural conversion was attained under relatively soft conditions, and the furfuryl alcohol selectivity was strongly affected by the chemical composition of the catalysts. Furfuryl alcohol (FA) was the major product in most cases, along with side products such as methylfuran (MF), furan, and traces of tetrahydrofuran (THF). These results showed that the PtPd bimetallic sample was more active relative to the monometallic counterparts. A correlation between the catalytic results and the physicochemical properties of the supported nanoparticles identified key factors responsible for the synergetic behavior of the PtPd system. The high activity and selectivity were due to the formation of ultra-small particles, alloy formation, and the Pt-rich surface composition of the bimetallic particles supported on the TiO2 nanowires.

Catalytic Upgrading of Biomass-Derived Sugars with Acidic Nanoporous Materials: Structural Role in Carbon-Chain Length Variation

Shifting from petroleum-based resources to inedible biomass for the production of valuable chemicals and fuels is one of the significant aspects in sustainable chemistry for realizing the sustainable development of our society. Various renowned biobased platform molecules, such as 5-hydroxymethylfurfural, furfural, levulinic acid, and lactic acid, are successfully accessible from the transformation of biobased sugars. To achieve the specific reaction routes, heterogeneous nanoporous acidic materials have served as promising catalysts for the conversion of bio-sugars in the past decade. This Review summarizes advances in various nanoporous acidic materials for bio-sugar conversion, in which the number of carbon atoms is variable and controllable with the assistance of the switchable structure of nanoporous materials. The major focus of this Review is on possible reaction pathways/mechanisms and the relationships between catalyst structure and catalytic performance. Moreover, representative examples of catalytic upgrading of biobased platform molecules to biochemicals and fuels through selective C-C cleavage and coupling strategies over nanoporous acidic materials are also discussed.

Synergistic effect between copper and different metal oxides in the selective hydrogenolysis of glucose

The coordination of copper and different acid/basic sites could promote the selective hydrogenolysis of glucose to polyols.

Effect of the surface acid sites of tungsten trioxide for highly selective hydrogenation of cellulose to ethylene glycol

This work studied a facile and template-free hydrothermal route for controlled synthesis of tungsten trioxide in the form of hexagonal nanorod (h-WO₃) and monoclinic nanosheet (m-WO₃). The surface morphology, crystal plane, surface bound water, and surface acid sites of the two kinds of WO₃ nanocrystals were investigated systematically. They were further evaluated as catalysts for selective cellulose hydrolysis. While both of them exhibited good catalytic performance, h-WO₃ was found to be more preferential for ethylene glycol (EG) generation. This catalytic performance relied on both the unique active crystal surface (1 0 0) and surface binding water (WO₃-H₂O) formed by h-WO₃ crystals, which provided more Lewis acid sites for degrading cellulose into EG. Results showed that the highest EG yield reaches 77.5% by a combination of loading 1 wt% Ru on the h-WO₃ catalyst.

Heterogeneously Catalyzed Hydrothermal Processing of C5-C6 Sugars

Biomass has been long exploited as an anthropogenic energy source; however, the 21st century challenges of energy security and climate change are driving resurgence in its utilization both as a renewable alternative to fossil fuels and as a sustainable carbon feedstock for chemicals production. Deconstruction of cellulose and hemicellulose carbohydrate polymers into their constituent C₅ and C₆ sugars, and subsequent heterogeneously catalyzed transformations, offer the promise of unlocking diverse oxygenates such as furfural, 5-hydroxymethylfurfural, xylitol, sorbitol, mannitol, and gluconic acid as biorefinery platform chemicals. Here, we review recent advances in the design and development of catalysts and processes for C₅-C₆ sugar reforming into chemical intermediates and products, and highlight the challenges of aqueous phase operation and catalyst evaluation, in addition to process considerations such as solvent and reactor selection.