Limit Test and pH Determination of 5-Hydroxymethylfurfural in Jiulongteng Honey

[Objectives]To explore the effect of storage time on pH and 5-hydroxymethylfurfural content in Jiulongteng honey.[Methods]The pH of Jiulongteng honey was determined by neutralization titration with sodium hydroxide standard solution.The content of 5-hydroxymethylfurfural in Jiulongteng honey was determined by HPLC.Chromatographic conditions:ZORBAX SB-C 18 column(250 mm×4.6 mm,5μm)from Agilent Co.,Ltd.,acetonitrile-0.1%formic acid solution(5:95)as mobile phase,flow rate of 0.8 mL/min,5-hydroxymethylfurfural detection wavelength of 284 nm,guanosine detection wavelength of 254 nm.[Results]The pH of 12 batches of Jiulongteng honey was 3.70-3.84 in the new honey stage,3.92-4.05 in the old honey stage 1,and 4.25-4.53 in the old honey stage 2;5-hydroxymethylfurfural was not detected in the new honey stage,5-hydroxymethylfurfural was detected in FM-001 in the old honey stage 1,and 5-hydroxymethylfurfural was detected in most samples in the old honey stage 2.[Conclusions]The pH and 5-hydroxymethylfurfural content of 12 batches of Jiulongteng honey met the requirements within 3 years of storage.There was no 5-hydroxymethylfurfural in Jiulongteng honey,but with the extension of storage time,the detection amount of 5-hydroxymethylfurfural increased significantly even if Jiulongteng honey was stored at low temperature.Therefore,5-hydroxymethylfurfural can be used as an important indicator of honey freshness.

Oxygen-vacancy-rich MnO_(x)supported RuO_(x)for efficient base-free oxidation of 5-hydroxymethylfurfural and 5-methoxymethylfurfural to 2,5-furandicarboxylic acid

2,5-Furandicarboxylic acid(FDCA)is a promising biomass-derived polymeric monomer that serves as an attractive alternative to terephthalic acid derived from fossil resources.However,the green and efficient production of FDCA through the oxidation of 5-hydroxymethylfurfural(HMF)and its derivatives is still rudimentary under base-free conditions.In this work,oxygen-vacancy-rich Mn Oxwas prepared and displayed a strong adsorption and anchoring ability to Ru species that mainly exposed the(210)plane of RuO_(2),bringing about highly dispersed and active interfacial Ru-O-Mn structures.Experimental results and density functional theory calculations confirm that these above features greatly facilitate the adsorption/activation of oxygen and the dehydrogenation-oxidation of HMF/5-methoxymethylfurfural(MMF),which enables an efficient FDCA production under base-free and mild conditions.Notably,a desirable FDCA yield of 86.56%was still obtained from concentrated HMF(10 wt%)under base-free conditions over oxygen-vacancy-rich Mn Oxsupported Ru Ox(1.0 MPaO_(2),120℃,6 h).This work delineates a facile catalyst preparation strategy for HMF/MMF oxidation,and might open a new avenue for the green synthesis of FDCA under base-free conditions.

Uncovering the electrooxidation behavior of 5-hydroxymethylfurfural on Ni/Co electrodes

Biomass,derived from plant photosynthesis that captures carbon dioxide to form carbohydrates,offers vast renewable reserves.The electrooxidation of biomass,coupled with the hydrogen evolution reaction,enables the simultaneous production of biomass-based plastic monomers and green hydrogen,attracting significant scholarly interest.However,ambiguity remains regarding the adsorption mechanism at the catalyst surface(Langmuir-Hinshelwood or Eley-Rideal)and the adsorbed substrate groups.To address this,we prepared a Ni/Co electrode for the electrooxidation of 5-hydroxymethylfurfural(HMF)into 2,5-furandicarboxylic acid(FDCA)through a corrosion reaction and electro-reduction pathway.HMF conversion reached 100.00%,FDCA yield reached 96.82%,and Faradic efficiency(FE)reached 92.14%.Meaningfully,utilizing in-situ spectroscopy and electrochemical methods,this work provided valuable insights into active sites and catalyst surface adsorption.

Realizing efficient electrochemical oxidation of 5-hydroxymethylfurfural on a freestanding Ni(OH)_(2)/nickel foam catalyst

With the continuous improvement of solar energy production capacity,how to effectively use the electricity generated by renewable solar energy for electrochemical conversion of biomass is a hot topic.Electrochemical conversion of 5-hydroxymethylfurfural(HMF)to biofuels and value-added oxygenated commodity chemicals provides a promising and alternative pathway to convert re-newable electricity into chemicals.Although nickel-based eletrocatalysts are well-known for HMF oxidation,their relatively low intrinsic activity,poor conductivity and stability still limit the poten-tial applications.Here,we report the fabrication of a freestanding nickel-based electrode,in which Ni(OH)2 species were in-situ constructed on Ni foam(NF)support using a facile ac-id-corrosion-induced strategy.The Ni(OH)2/NF electrocatalyst exhibits stable and efficient electro-chemical HMF oxidation into 2,5-furandicarboxylic acid(FDCA)with HMF conversion close to 100%with high Faraday efficiency.In-situ formation strategy results in a compact interface between Ni(OH)2 and NF,which contributes to good conductivity and stability during electrochemical reac-tions.The superior performance benefits from dynamic cyclic evolution of Ni(OH)2 to NiOOH,which acts as the reactive species for HMF oxidation to FDCA.A scaled-up device based on a continu-ous-flow electrolytic cell was also established,giving stable operation with a high FDCA production rate of 27 mg h^(-1)cm^(−2).This job offers a straightforward,economical,and scalable design strategy to design efficient and durable catalysts for electrochemical conversion of valuable chemicals.

Transforming liquid flow fuel cells to controllable reactors for highlyefficient oxidation of 5-hydroxymethylfurfural to 2, 5-furandicarboxylic acid at low temperature

Highly-efficient oxidation of 5-hydroxymethylfurtural(HMF) to 2,5-furandicarboxylic acid(FDCA) at low temperature with air as the oxidant is still challenging.Herein,inspired by the respirato ry electron transport chain(ETC) of living cells mediated by electron carriers,we constructed artificial ETCs and transformed liquid flow fuel cells(LFFCs) to flexible reactors for efficient oxidation of HMF to produce FDCA under mild conditions.This LFFC reactor employed an electrodeposition modified nickel foam as an anode to promote HMF oxidation and(VO_(2))_(2)SO_(4) as a cathode electron carrier to facilitate the electron transfer to air.The reaction rate could be easily controlled by selecting the anode catalyst,adjusting the external loading and changing the cathodic electron carrier or oxidants.A maximal power density of 44.9 mW cm^(-2) at room temperature was achieved,while for FDCA production,short-circuit condition was preferred to achieve quick transfer of electrons.For a single batch operation with 0.1 M initial HMF,FDCA yield reached 97.1%.By fed-batch operation,FDCA concentration reached 144.5 g L^(-1) with a total yield of 96%.Ni^(2+)/Ni^(3+) redox couple was the active species mediating the electron transfer,while both experimental and DFT calculation results indicated that HMFCA pathway was the preferred reaction mechanism.

Enhancing the Electrocatalytic Oxidation of 5-Hydroxymethylfurfural Through Cascade Structure Tuning for Highly Stable Biomass Upgrading

Electrocatalytic 5-hydroxymethylfurfural oxidation reaction(HMFOR)provides a promising strategy to convert biomass derivative to highvalue-added chemicals.Herein,a cascade strategy is proposed to construct Pd-NiCo_(2)O_(4)electrocatalyst by Pd loading on Ni-doped Co3O4 and for highly active and stable synergistic HMF oxidation.An elevated current density of 800 mA cm^(-2)can be achieved at 1.5 V,and both Faradaic efficiency and yield of 2,5-furandicarboxylic acid remained close to 100%over 10 consecutive electrolysis.Experimental and theoretical results unveil that the introduction of Pd atoms can modulate the local electronic structure of Ni/Co,which not only balances the competitive adsorption of HMF and OH-species,but also promote the active Ni^(3+)species formation,inducing high indirect oxidation activity.We have also discovered that Ni incorporation facilitates the Co2+pre-oxidation and electrophilic OH*generation to contribute direct oxidation process.This work provides a new approach to design advanced electrocatalyst for biomass upgrading.

Facet effect on the reconstructed Cu-catalyzed electrochemical hydrogenation of 5-hydroxymethylfurfural(HMF) towards 2,5-bis(hydroxymethy)furan (BHMF)

The electrochemical hydrogenation of HMF to BHMF is an elegant alternative to the conventio nal thermocatalytic route for the production of high-value-added chemicals from biomass resources.In virtue of the wide potential window with promising Faradic efficiency(FE) towards BHMF,Cu-based electrode has been in the center of investigation.However,its structure-activity relationship remains ambiguous and its intrinsic catalytic activity is still unsatisfactory.In this work,we develop a two-step oxidation-reduction strategy to reconstruct the surface atom arrangement of the Cu foam(CF).By combination of multiple quasi-situ/in-situ techniques and density functional theory(DFT) calculation,the critical factor that governs the reaction is demonstrated to be facet effect of the metallic Cu crystal:Cu(110) facet accounts for the most favorable surface with enhanced chemisorption with reactants and selective production of BHMF,while Cu(100) facet might trigger the accumulation of the by-product 5,5'-bis(hydroxy methy)hydrofurion(BHH).With the optimized composition of the facets on the reconstructed Cu(OH)_(2)-ER/CF,the performance could be noticeably enhanced with a BHMF FE of 92.3% and HMF conversion of 98.5% at a potential of -0.15 V versus reversible hydrogen electrode(vs.RHE) in 0.1 M KOH solution.This work sheds light on the incomplete mechanistic puzzle for Cu-catalyzed electrochemical hydrogenation of HMF to BHMF,and provides a theoretical foundation for further precise design of highly efficient catalytic electrodes.

Au^(δ-)-O_(v)-Ti^(3+):Active site of MO_(x)-Au/TiO_(2) catalysts for the aerobic oxidation of 5-hydroxymethylfurfural

Despite wide applications of noble metal-based catalysts in 5-hydroxymethylfurfural(HMF)oxidation,promoting the catalytic performance at low loading amounts still remains a significant challenge.Herein,a series of metal oxide modified MO_(x)-Au/TiO_(2)(M=Fe,Co,Ni)catalysts with low Au loading amount of 0.5 wt%were synthesized.Addition of transition metal oxides promotes electron transfer and generation of the Au^(δ-)-O_(v)-Ti^(3+)interface.A combination study reveals that the dual-active site(Au^(δ-)-O_(v)-Ti^(3+))governs the catalytic performance of the ratedetermining step,namely hydroxyl group oxidation.Au^(δ-) site facilitates chemisorption and activation of O_(2) molecules.At the same time,O_(v)-Ti^(3+) site acts as the role of“killing two birds with one stone”:enhancing adsorption of both reactants,accelerating the activation and dissociation of H_(2)O,and facilitating activation of the adsorbed O_(2).Besides,superoxide radicals instead of base is the active oxygen species during the rate-determining step.On this basis,a FDCA yield of 71.2% was achieved under base-free conditions,complying with the“green chemistry”principle.This work provides a new strategy for the transition metal oxides modification of Au-based catalysts,which would be constructive for the rational design of other heterogeneous catalysts.

Conversion of Cellulose to 5-Hydroxymethylfurfural in Water- Tetrahydrofuran and Byproducts Identification

Conversion of cellulose into platform chemical 5-hydroxymethylfurfural （HMF） in water-tetrahydrofuran （THF） co-solvents under acidic condition was studied. 38.6% of HMF was obtained with low cellulose concentration of 2.4wt%, but levulinic acid （LA） and solid humins became the main products with high cellulose concentration. The soluble byproducts were analyzed by high performance liquid chromatography/multiple stage tandem mass spec-trometry, and chemicals with formula of C9H16O4、 C10H14O4、 C11H12O4、C12H10O5 and C12H16O8 were detected. THF could participate in the reaction via ring-opening into 1,4-butanediol followed by esterification with LA into C9H16O4 or etherification with HMF into C10H14O4. C11H12O4 was formed by esterification of HMF with LA, C12H10O5 was formed by self-etherification of HMF, while C12H16O8 was formed by acetalization of HMF with glucose. Self-etherification of HMF and etherification of HMF with 1,4-butanediol were identified as two main side reactions.

Preparation of 5-Hydroxymethylfurfural from Cellulose via Fast Depolymerization and Consecutively Catalytic Conversion

The conversion of cellulose to 5-hydroxymethylfurfural （HMF） has been investigated by a one-pot consecutive reaction. At first, cellulose was depolymerised into glucose via a fast degradation of cellulose in molten ZnCI~ in the presence of hydrochloric acid, and the yield of glucose is 75% in 120 s at reaction temperature of 95 ℃. Then, DMSO was used as solvent and different kinds of metal chloride were added as catalysts, and the conversion was carried out continuously at 110-130 ℃ for 0.5-4 h. The yield of HMF was 53% when CrC13 were used as catalyst. The one-pot two steps conversion was carried out at atmosphere pressure, and it is a simple route to prepare HMF from lignocellulosic feedstock on a large scale.

2,5-Furandicarboxylic acid production via catalytic oxidation of 5-hydroxymethylfurfural:Catalysts,processes and reaction mechanism

Biomass conversion to value-added chemicals has received tremendous attention for solving global warming issues and fossil fuel depletion.5-Hydroxymethylfurfural(HMF)is a key bio-based platform molecule to produce many useful organic chemicals by oxidation,hydrogenation,polymerization,and ring-opening reactions.Among all derivatives,the oxidation product 2,5-furandicarboxylic acid(FDCA)is a promising alternative to petroleum-based terephthalic acid for the synthesis of biodegradable plastics.This review analytically discusses the recent progress in the thermocatalytic,electrocatalytic,and photocatalytic oxidation of HMF into FDCA,including catalyst screening,synthesis processes,and reaction mechanism.Rapid fundamental advances may be possible in non-precious metal and metal-free catalysts that are highly efficient under the base-free conditions,and external field-assisted processes like electrochemical or photoelectrochemical cells.

Efficient conversion of fructose to 5-hydroxymethylfurfural over sulfated porous carbon catalyst

Sulfated porous carbon （PC-SO3H） catalyst was successfully synthesized from one-pot treatment of porous polydivinylbenzene in H2SO4 at 250 ℃, which exhibited very good catalytic performances in the production of 5-hydroxymethylfurfural from fructose.

Functionalized metal-organic frameworks with strong acidity and hydrophobicity as an efficient catalyst for the production of 5-hydroxymethylfurfural

In the dehydration of fructose to 5-hydroxymethyl furfural(HMF),in situ produced water weakens the acid strength of the catalyst and causes the rehydration of HMF,causing unsatisfactory catalytic activity and selectivity.In this work,a class of benzenesulfonic acid-grafted metal-organic frameworks with strong acidity and hydrophobicity is obtained by the direct sulfonation method using 4-chlorobenzenesulfonic acid as sulfonating agent.The resultant MOFs have a specific surface area of greater than 250 m^(2)·g^(-1),acid density above 1.0 mmol·g^(-1),and water contact angle up to 129°.The hydrophobic MOF-PhSO_(3)H exhibits both higher catalytic activity and selectivity than MOF-SO_(3)H in the HMF synthesis due to its better hydrophobicity and olephilicity.Moreover,the catalyst has a high recycled stability.At last,fructose is completely converted,and 98.0%yield of HMF is obtained under 120℃ in a DMSO solvent system.The successful preparation of the hydrophobic acidic MOF provides a novel hydrophobic catalyst for the synthesis of HMF.

Selective oxidation of biomass derived 5-hydroxymethylfurfural to 2,5-diformylfuran using sodium nitrite

A mild and simple process for the effective oxidation of 5-hydroxymethylfurfural（HMF） into 2,5-diformylfuran（DFF） has been developed using Na NO2 as the oxidant. Some important reaction parameters were investigated to optimize the oxidation of HMF into DFF. It was found that the reaction solvent was very crucial for this reaction. Trifluoroacetic acid was the best solvent for the oxidation of HMF into DFF by Na NO2.Under the optimal reaction condition, almost quantitative HMF conversion and high DFF yield of 90.4% were obtained after 1 h at room temperature.

Highly efficient production of 2,5-dihydroxymethylfuran from biomass-derived 5-hydroxymethylfurfural over an amorphous and mesoporous zirconium phosphonate catalyst

The development of high-efficiency and low-cost catalysts is very crucial for the MeerweinPonndorf-Verley (MPV) reduction of biomass-derived 5-hydroxymethylfurfural (HMF) into 2,5-dihydroxymethylfuran (DHMF). In this work, an amorphous and mesoporous zirconium phosphonate catalyst (Zr-DTMP), which is a zirconium-containing organic-inorganic nanohybrid, was successfully designed and synthesized by the simple assembly of zirconium tetrachloride (ZrCl4) and diethylene triaminepenta(methylene phosphonic acid)(DTMP). Satisfactorily, when Zr-DTMP was employed for the MPV reduction of HMF in the presence of 2-butanol (secBuOH), DHMF yield could be achieved as 96.5% in 3 h under a relatively mild reaction temperature of 140℃. Systematic investigations indicated that this high catalytic activity should be mainly due to the cooperative role of enhancive Lewis acid site (Zr4+) and Lewis base site (O2-) in activating the carbonyl group of HMF and dissociating the hydroxyl group of secBuOH, respectively. Additionally, Zr-DTMP showed excellent catalytic stability, when it was successively used 5 recycles, its surface characteristics and textural properties still remained almost unchanged, and so, the catalytic activity was not obviously affected. More interestingly, Zr-DTMP could also be applied for the selective reduction of other biomass-derived carbonyl compounds, such as 5-methylfurfural (MF), furfural (FF), levulinic acid (LA), ethyl levulinate (EL) and cyclohexanone (CHN), into the corresponding products with high yields, which is beneficial to the effective synthesis of various valuable bio-based chemicals.

A Low-Cost and Easily Prepared Manganese Carbonate as an Effi cient Catalyst for Aerobic Oxidation of 5-Hydroxymethylfurfural to 2,5-Diformylfuran

A low-cost and easily prepared manganese carbonate(Mn CO_3) has been synthesized for catalytic conversion of 5-hydroxymethylfurfural(5-HMF) to 2,5-diformylfuran(DFF). The properties and morphology of the manganese carbonate were measured by SEM,XRD,TGA,BET and XPS. In this method,no harsh reaction conditions were required,and it was a simple and green process for the oxidation of 5-HMF into DFF. To achieve an optimum DFF yield,different reaction conditions,including reaction temperature,reaction time,catalyst amount,and solvents were investigated. Results from the experiments indicated that the highest DFF yield of 86.9% was obtained at 120 °C under atmospheric oxygen pressure after 6h. Finally,Mn CO_3 could be used at least five times with considerable stability.

Fabricating amide functional group modified hyper-cross-linked adsorption resin with enhanced adsorption and recognition performance for 5-hydroxymethylfurfural adsorption via simple one-step

In this study,three kinds of amide functional group modified hyper-cross-linked adsorption resin were synthesized by alternating radical copolymerization in simple one-step and applied for 5-hydroxymethylfurfural(5-HMF)adsorption.The successful synthesis and properties of adsorbents were evaluated with Fourier transform infrared spectroscopy,scanning electron microscopy,nitrogen adsorption-desorption isotherms,thermogravimetric analysis,and elemental analysis.Poly(N,N’-4,4’-diphenyl methane-bismaleimide-alt-divinylbenzene)(poly(BDM-alt-DVB))resin exhibited highest adsorption capacity for 5-HMF(64.0 mg·g^(-1)wet resin)and excellent adsorption selectivity(a_(5-HMF/LA)=2.71±0.12,α_(5-HMF/FA)=13.88±0.15,α_(5-HMF/Glucose)=11.91±1.11)in the multi-component solution at 25℃.Langmuir isotherm model well fitted the equilibrium adsorption data within the initial 5-HMF concentration range of 0.5-10.0 g·L^(-1) with highest correlation coefficient.Furthermore,the thermodynamic parameters demonstrated that the adsorption of 5-HMF onto poly(BDM-alt-DVB)resin was spontaneous and exothermic.Kinetic study revealed that the adsorption process was fast,reaching equilibrium within12 min.Importantly,the poly(BDM-alt-DVB)resin also demonstrated excellent reusability.In summary,the poly(BDM-alt-DVB)resin will be useful in 5-HMF hydrolysate separation applications.

Adjacent acid sites cooperatively catalyze fructose to 5-hydroxymethylfurfural in a new, facile pathway

To study the effect of adjacent hydroxyl to the active sites, several acid catalysts, i.e. substituted benzoic acids with adjacent carboxyl are employed in the fructose dehydration to 5-hydroxymethylfurfural(HMF).Experimental results reveal that Br?nsted acid sites with adjacent carboxyl present higher catalytic ability than isolated ones. Computational results suggest that the adjacent sites lead to co-interaction on fructose, corresponding more stable transition state and faster HMF formation rate. Based on the enhancement from the adjacent sites, a novel ordered mesoporous carbon(OMC) full of carboxyls in surface is prepared and turns out to be an effective solid catalyst for HMF production from fructose derived from biomass.

Base-free oxidative esterification of 5-hydroxymethylfurfural to furan-2,5-dimethylcarboxylate over n-doped carbon-supported Co/Fe bimetallic catalyst under batch-operation or continuous-flow conditions

Developing an efficient and easily available catalyst for the selective conversion of biomass-derived 5-hydroxymethylfurfural(HMF)into furan-2,5-dimethylcarboxylate(FDMC),a valuable biomass-based monomer,remains a high demand but formidable challenge.Herein,a facile strategy for the synthesis of N-doped carbon-supported Co/Fe bimetallic catalyst(CoFe-NC)was developed,which provided an outstanding FDMC yield of 93%in a batch reactor(base-free,80℃,2 bar O_(2),4 h).Interestingly,CoFe-NC also gave a high FDMC yield of 91%under continuous-flow conditions for 80 h(5 bar O_(2),80℃,GHSV 1320 h^(-1),LHSV 0.6 h^(-1),base-free).Notably,it is the first time that a non-noble catalyst gave such a high FDMC yield under continuous-flow conditions.The introduction of Fe could greatly improve both the electron intensity of Co-N_(x)species and basicity of the catalyst,which endowed CoFe-NC with improved O_(2)activation capacity and enhanced dehydrogenation activity for the oxidation-esterification of HMF.This work delineates the efficient strategy on the construction of N-doped carbon-supported non-noble catalyst,which might open a new avenue for developing highly efficient catalyst for FDMC production.