Functionalized partially hydroxylated MgF2 as catalysts for the dehydration of d-xylose to furfural

Cu/SiO2 synthesized with HKUST-1 as precursor: high ratio of Cu+/(Cu+ + Cu0) and rich oxygen defects for efficient catalytic hydrogenation of furfural to 2-methyl furan

Cu/SiO2 is one of the most promising catalysts for the furfural (FF) hydrogenation reaction but suffers from the difficulty of tailoring the microstructure and surface properties. Herein, we developed a MOF-derived Cu/SiO2 catalyst (Cu/SiO2-MOF) for FF hydrogenation to 2-methyl furan (2-MF). In comparison with Cu/SiO2 catalysts prepared from ammonia evaporation (Cu/SiO2-AE) and traditional impregnation (Cu/SiO2-TI), the copper species in Cu/SiO2-MOF could not only be anchored on the silica surface via forming Cu-O-Si bonds but also exposed many more active sites. In this way, a higher ratio of Cu+/(Cu+ + Cu0) and richer oxygen defects were constructed via strong metal-support interactions, which were responsible for the superior catalytic performance. In addition, it was found that the solvent effect on product distribution played an important role in adjusting the selectivity to 2-MF and cyclopentanone (CPO). The present work not only provides a deep insight into the catalytic mechanism of Cu/SiO2-MOF for the FF hydrogenation reaction but also sheds light on the design and synthesis of highly efficient catalysts for other heterogeneous catalysis fields.

Thermal Stability for the Continuous Production of γ-Valerolactone from the Hydrogenation of N-Butyl Levulinate in a CSTR

γ-valerolactone can be a game-changer in the chemical industry because it could substitute fossil feedstocks in different fields. Its production is from the hydrogenation of levulinic acid or alkyl levulinates and can present some risk of thermal runaway. To the best of our knowledge, no studies evaluate the thermal stability of this production in a continuous reactor. We simulated the thermal behavior of the hydrogenation of butyl levulinate over Ru/C in a continuous stirred-tank reactor and performed a sensitivity analysis. The kinetic and thermodynamic constants from Wang et al.’s articles were used. We found that the risk of thermal stability is low for this chemical system.

Nano metal fluorides: small particles with great properties

The recently developed fluorolytic sol–gel route to metal fluorides opens a very broad range of both scientific and technical applications of the accessible high surface area metal fluorides, many of which have already been applied or tested. Specific chemical properties such as high Lewis acidity and physical properties such as high surface area, mesoporosity and nanosize as well as the possibility to apply metal fluorides on surfaces via a non-aqueous sol make the fluorolytic synthesis route a very versatile one. The scope of its scientific and technical use and the state of the art are presented.

Improved conversion of bamboo shoot shells to furfuryl alcohol and furfurylamine by a sequential catalysis with sulfonated graphite and biocatalysts

Furfurylamine and furfuryl alcohol are known as important furfural-upgrading derivatives in the production of pharmaceuticals, fibers, additives, polymers, etc. In a one-pot manner, the catalysis of biomass into furan-based chemicals was established in a tandem reaction with sulfonated Sn–graphite catalysts and biocatalysts. Using a raw bamboo shoot shell (75.0 g L⁻¹) as the feedstock, a high furfural yield of 41.1% (based on xylan) was obtained using the heterogeneous Sn–graphite catalyst (3.6 wt% dosage) in water (pH 1.0) for 30 min at 180 °C. Under the optimum bioreaction conditions, the biomass-derived furfural could be transformed into furfuryl alcohol (0.310 g furfuryl alcohol per g xylan in biomass) by a reductase biocatalyst or furfurylamine (0.305 g furfurylamine per g xylan in biomass) using an ω-transaminase biocatalyst. Such one-pot chemoenzymatic processes combined the merits of both heterogeneous catalysts and biocatalysts, and sustainable processes were successfully constructed for synthesizing key bio-based furans.

Furfurylamine and furfuryl alcohol are known as important furfural-upgrading derivatives in the production of pharmaceuticals, fibers, additives, polymers, etc.

Nb-doped variants of high surface aluminium fluoride: a very strong bi-acidic solid catalyst

Novel aluminium Nb-doped fluoride catalysts were synthesized using an aluminium hydroxide precursor to afford solids where very strong Lewis acid sites coexist with Brønsted acid sites.

Rational design of MgF2 catalysts with long-term stability for the dehydrofluorination of 1,1-difluoroethane (HFC-152a)

In this study, three different approaches, i.e. the sol–gel method, precipitation method and hard-template method, were applied to synthesize MgF₂ catalysts with improved stability towards the dehydrofluorination of hydrofluorocarbons (HFCs); the in situ XRD technique was employed to investigate the relationship between the calcination temperature and the crystallite size of precursors to determine optimal calcination temperature for the preparation of the MgF₂ catalysts. Moreover, the physicochemical properties of MgF₂ catalysts were examined via BET, XRD, EDS and TPD of NH₃ and compared. Undoubtedly, the application of different methods had a significant influence on the surface properties and catalytic performances of MgF₂ catalysts. The surface areas of the catalysts prepared by the precipitation method, sol–gel method and template method were 120, 215 and 304 m² g⁻¹, respectively, upon calcination at 200 °C. However, the surface area of the MgF₂ catalysts decreased significantly when the calcination temperatures of 300 and 350 °C were applied. The catalytic performance of these catalysts was evaluated via the dehydrofluorination of 1,1-difluoroethane (HFC-152a). The MgF₂ catalyst prepared by the precipitation method showed the lowest catalytic activity among all the MgF₂ catalysts. When the calcination temperature was above 300 °C, the MgF₂ catalysts prepared via the template method demonstrated the highest catalytic conversion rate with catalytic activity following the order: MgF₂-T (template method) > MgF₂-S (sol–gel method) > MgF₂-P (precipitation method). The conversion rate generally agreed with the total amount of acid on the surface of the catalysts, which was measured by the NH₃-TPD technique. The MgF₂-T catalysts were further examined for the dehydrofluorination of HFC-152a for 600 hours, and a conversion rate greater than 45% was maintained, demonstrating superior long-term stability of these catalysts.

In this study, sol–gel, precipitation and hard-template methods were applied to synthesize MgF₂ catalysts with improved stability towards dehydrofluorination of hydrofluorocarbons and MgF₂-T catalysts demonstrated superior long-term stability.

Efficient transformation of corn stover to furfural using p-hydroxybenzenesulfonic acid-formaldehyde resin solid acid

In this work, p-hydroxybenzenesulfonic acid-formaldehyde resin acid catalyst (MSPFR), was synthesized by a hydrothermal method, and employed for the furfural production from raw corn stover. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ adsorption-desorption, elemental analysis (EA), thermogravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FT-IR) were used to characterize the MSPFR. The effects of reaction time, temperature, solvents and corn stover loading were investigated. The MSPFR presented high catalytic activity for the formation of furfural from corn stover. When the MSPFR/corn stover mass loading ratio was 0.5, a higher furfural yield of 43.4% could be achieved at 190 °C in 100 min with 30.7% 5-hydroxymethylfurfural (HMF) yield. Additionally, quite importantly, the recyclability of the MSPFR for xylose dehydration is good, and for the conversion of corn stover was reasonable.

Hydrolysis of Hemicellulose and Derivatives-A Review of Recent Advances in the Production of Furfural

Biobased production of furfural has been known for decades. Nevertheless, bioeconomy and circular economy concepts is much more recent and has motivated a regain of interest of dedicated research to improve production modes and expand potential uses. Accordingly, this review paper aims essentially at outlining recent breakthroughs obtained in the field of furfural production from sugars and polysaccharides feedstocks. The review discusses advances obtained in major production pathways recently explored splitting in the following categories: (i) non-catalytic routes like use of critical solvents or hot water pretreatment, (ii) use of various homogeneous catalysts like mineral or organic acids, metal salts or ionic liquids, (iii) feedstock dehydration making use of various solid acid catalysts; (iv) feedstock dehydration making use of supported catalysts, (v) other heterogeneous catalytic routes. The paper also briefly overviews current understanding of furfural chemical synthesis and its underpinning mechanism as well as safety issues pertaining to the substance. Eventually, some remaining research topics are put in perspective for further optimization of biobased furfural production.

Modifying the reactivity of a solid Lewis acid: niobium and antimony doped nanoscopic aluminum fluoride

A series of acid catalysts were prepared, using niobium and antimony as dopants in the fluorolytic sol–gel synthesis of high surface aluminium fluoride.

Chemical-enzymatic conversion of corncob-derived xylose to furfuralcohol by the tandem catalysis with SO42-/SnO2-kaoline and E. coli CCZU-T15 cells in toluene-water media

One-pot synthesis of furfuralcohol from corncob-derived xylose was attempted by the tandem catalysis with solid acid SO₄^2-/SnO₂-kaoline and recombination Escherichia coli CCZU-T15 whole-cells in the toluene-water media. Using SO₄^2-/SnO₂-kaoline (3.5wt%) as catalyst, the furfural yield of 74.3% was obtained from corncob-derived xylose in the toluene-water (1:2, v:v) containing 10mM OP-10 at 170°C for 30min. After furfural liquor was mixed with corncob-hydrolysate from the enzymatic hydrolysis of oxalic acid-pretreated corncob residue, furfural (50.5mM) could be completely biotransformed to furfuralcohol with Escherichia coli CCZU-T15 whole-cells harboring an NADH-dependent reductase (ClCR) in the toluene-water (1:3, v:v) containing 12.5mM OP-10 and 1.6mM glucose/mM furfural at 30°C and pH 6.5. Furfuralcohol was obtained at 13.0% yield based on starting material corncob (100% furfuralcohol yield for bioreduction of furfural step). Clearly, this one-pot synthesis of furfuralcohol strategy shows high potential application for the effective utilization of corncob.

One-pot chemo-enzymatic synthesis of furfuralcohol from xylose

Furfuralcohol (FOL) is an important intermediate for the production of lysine, ascorbic acid, and lubricants. It can be used as a hypergolic fuel in rocketry. In this study, it was attempted to synthesize FOL from xylose by tandem catalysis with solid acid SO₄^2-/SnO₂-Montmorillonite and recombination Escherichia coli CCZU-K14 whole cells. Using SO₄^2-/SnO₂-Montmorillonite (3.0wt% dosage) as catalyst, a highest furfural yield of 41.9% was achieved from xylose at 170°C for 20min. Furthermore, Escherichia coli CCZU-K14 whole cells were used for bioconverting furfural to FOL. The optimum biocatalytic reaction temperature, reaction pH, cosubstrate concentration, and substrate concentration were 30°C, 6.5, 1.5mol glucose/mol furfural, and 200mM, respectively. Finally, the yield of FOL from 200mM furfural was achieved to 100% by Escherichia coli CCZU-K14 whole cells after 24h. In conclusion, this strategy show high potential application for the effective synthesis of FOL.

Catalytic conversion of xylose and corn stalk into furfural over carbon solid acid catalyst in γ-valerolactone

A novel carbon solid acid catalyst was synthesized by the sulfonation of carbonaceous material which was prepared by carbonization of sucrose using 4-BDS as a sulfonating agent. TEM, N2 adsorption-desorption, elemental analysis, XPS and FT-IR were used to characterize the catalyst. Then, the catalyst was applied for the conversion of xylose and corn stalk into furfural in GVL. The influence of the reaction time, temperature and dosage of catalyst on xylose dehydration were also investigated. The Brønsted acid catalyst exhibited high activity in the dehydration of xylose, with a high furfural yield of 78.5% at 170°C in 30min. What's more, a 60.6% furfural yield from corn stalk was achieved in 100min at 200°C. The recyclability of the sulfonated carbon catalyst was perfect, and it could be reused for 5times without the loss of furfural yields.

The non-aqueous fluorolytic sol-gel synthesis of nanoscaled metal fluorides

This review article focuses on the mechanism of the non-aqueous fluorolytic sol gel-synthesis of nanoscopic metal fluorides and hydroxide fluorides. Based on MAS-NMR, XRD, WAXS and SAXS investigations in combination with computational calculations, it is shown that a stepwise replacement of alkoxide by F-ions takes place resulting in the formation of a large variety of metal alkoxide fluoride clusters, some of them being isolated and structurally characterised. It is shown that these nanoscopic metal fluorides obtained via this new synthesis approach exhibit distinctly different properties compared with their classically prepared homologues. Thus, extremely strong solid Lewis acids are available which give access to new catalytic reactions with sometimes unexpectedly high conversion degrees and selectivity. Even more interestingly, metal hydroxide fluorides can be obtained via this synthesis route that are not accessible via any other approach for which the hydroxide to fluoride ratios can be adjusted over a wide range. Optically fully transparent sols obtained in this way can be used for the first time to manufacture antireflective coatings, corundum ceramics with drastically improved properties as well as novel metal fluoride based organic-inorganic composites. The properties of these new fluoride based materials are presented and discussed in context with the above mentioned new fields of application.

Efficient conversion of glucose to 5-hydroxymethylfurfural using bifunctional partially hydroxylated AlF3

Mesoporous AlF₃ material bearing both Lewis and Brønsted acid sites exhibits high catalytic performance in glucose-to-fructose isomerization and subsequent dehydration to HMF (57.3% yield).

Gas-phase cascade upgrading of furfural to 2-methylfuran using methanol as a H-transfer reactant and MgO based catalysts

The one-pot hydrogenolysis of furfural to 2-methylfuran in the gas phase is catalysed by Mg/Fe mixed oxide using methanol as the H-transfer reactant.

Regeneration of surface acid sites via mild oxidation on dehydration catalysts

This work reports novel experimental evidence for the use of mild oxidation conditions to remove humin deposits on active xylose dehydration catalysts that showed deactivation.

Highly dispersed Cu nanoparticles as an efficient catalyst for the synthesis of the biofuel 2-methylfuran

An AE-Cu/SiO₂ catalyst obtained a 95.5% yield for 2-methylfuran due to the cooperative contribution of Cu nanoparticles, Cu⁺ species and acid sites.

Hydrolysis of Selected Tropical Plant Wastes Catalyzed by a Magnetic Carbonaceous Acid with Microwave

In this study, magnetic carbonaceous acids were synthesized by pyrolysis of the homogeneous mixtures of glucose and magnetic Fe3O4 nanoparticles, and subsequent sulfonation. The synthesis conditions were optimized to obtain a catalyst with both high acid density (0.75 mmol g(-1)) and strong magnetism [magnetic saturation, Ms = 19.5 Am(2) kg(-1)]. The screened catalyst (C-SO3H/Fe3O4) was used to hydrolyze ball-milled cellulose in a microwave reactor with total reducing sugar (TRS) yield of 25.3% under the best conditions at 190 °C for 3.5 h. It was cycled for at least seven times with high catalyst recovery rate (92.8%), acid density (0.63 mmol g(-1)) and magnetism (Ms = 12.9 Am(2) kg(-1)), as well as high TRS yield (20.1%) from the hydrolysis of ball-milled cellulose. The catalyst was further successfully tested for the hydrolysis of tropical biomass with high TRS and glucose yields of 79.8% and 58.3% for bagasse, 47.2% and 35.6% for Jatropha hulls, as well as 54.4% and 35.8% for Plukenetia hulls.

One-step Conversion of Furfural into 2-Methyltetrahydrofuran under Mild Conditions

One-step direct conversion of biomass-derived furfural to 2-methyltetrahydrofuran was realized under atmospheric pressure over a dual solid catalyst based on two-stage-packed Cu-Pd in a reactor; this is the first report that one-step conversion of furfural resulted in high yield of 2-methyltetrahydrofuran (97.1 %) under atmospheric pressure. This strategy provided a successive hydrogenation process, which avoids high H2 pressure, uses the reactor efficiently, and eliminates the product-separation step. Therefore, it could enhance the overall efficiency as a result of low cost and high yield.

Tuning the surface properties of novel ternary iron(III) fluoride-based catalysts using the template effect of the matrix

Sol-gel prepared ternary FeF3-MgF2 materials have become promising heterogeneous catalysts due to their porosity and surface Lewis/Brønsted acidity (bi-acidity). Despite the good catalytic performance, nanoscopic characterisations of this type of material are still missing and the key factors controlling the surface properties have not yet been identified, impeding both a better understanding and further development of ternary fluoride catalysts. In this study, we characterised the interaction between the bi-acidic component (FeF3) and the matrix (MgF2) on the nano-scale. For the first time, the formation pathway of FeF3-MgF2 was profiled and the template effect of MgF2 during the synthesis process was discovered. Based on these new insights two novel materials, FeF3-CaF2 and FeF3-SrF2, were established, revealing that with decreasing the atomic numbers (from Sr to Mg), the ternary fluorides exhibited increasing surface acidity and surface area but decreasing pore size. These systematic changes gave rise to a panel of catalysts with tuneable surface and bulk properties either by changing the matrix alkaline earth metal fluoride or by adjusting their ratios to Fe or both. The template effect of the alkaline earth metal fluoride matrix was identified as the most probable key factor determining the surface properties and further influencing the catalytic performance in ternary fluoride based catalysts, and paves the way to targeted design of next-generation catalysts with tunable properties.

Quantification of acidic sites of nanoscopic hydroxylated magnesium fluorides by FTIR and 15N MAS NMR spectroscopy

A new method is described for the calculation of molar extinction coefficients for quantitative FTIR measurements of acidic surface sites.

Beta zeolite: a universally applicable catalyst for the conversion of various types of saccharides into furfurals

Beta zeolite having both Lewis and Brønsted acid sites universally promoted direct conversion of various types of saccharides into furfurals.

Nanoscale metal fluorides: a new class of heterogeneous catalysts

Nanoscale metal fluorides and hydroxide fluorides prepared according the fluorolytic sol–gel synthesis represent a powerful class of bi-acidic heterogeneous catalysts.

Antireflective coatings with adjustable refractive index and porosity synthesized by micelle-templated deposition of MgF2 sol particles

Minimizing efficiency losses caused by unwanted light reflection at the interface between lenses, optical instruments and solar cells with the surrounding medium requires antireflective coatings with adequate refractive index and coating thickness. We describe a new type of antireflective coating material with easily and independently tailorable refractive index and coating thickness based on the deposition of colloidal MgF2 nanoparticles. The material synthesis employs micelles of amphiphilic block copolymers as structure directing agent to introduce controlled mesoporosity into MgF2 film. The coatings thickness can be easily adjusted by the applied coating conditions. The coatings refractive index is determined by the materials porosity, which is controlled by the amount of employed pore template. The refractive index can be precisely tuned between 1.23 and 1.11, i.e., in a range that is not accessible to nonporous inorganic materials. Hence, zero reflectance conditions can be established for a wide range of substrate materials.

Dehydration of xylose and glucose to furan derivatives using bifunctional partially hydroxylated MgF2 catalysts and N2-stripping

The current furfural production yield is low due to the use of non-selective homogeneous catalysts and expensive separation.