•Two highly active catalytic species are generated from the 2D Co-based MOFs.•The active species exhibit high activities for oxidative condensation of furfural.•A 99% selectivity of 3-(furan-2-yl-)-2-methylacrylaldehyde has been obtained.•The relationship between reaction activity and catalyst structure is discussed.•No Co leaches and the observed catalysis (ACS-I and ACS-II) is truly heterogeneous in nature.We report a facile method for gaining two different types of highly active species from the same 2D Co-based MOFs, which can effectively catalyze the selective transformation of biomass-derived furfural (FUR) in alcohols. Removal of the coordinated water molecules from the Co-based MOFs at 300 °C creates the open metal centers as catalytic active species (designated as ACS-I catalyst). Increasing the pyrolysis temperature to 700 °C, the derived multi-element carbon-matrix nanocomposite from the MOFs (designated as ACS-II catalyst) also shows highly catalytic performance. Both catalyst ACS-I and ACS-II exhibit high reactivity (84.9% conv.) and excellent selectivity (ca. 99.0%) in the oxidative condensation of FUR with n-propanol to produce 3-(furan-2-yl-)-2-methylacrylaldehyde (2) in the presence of molecular oxygen. The particular evidence for the role of metal Co centers in ACS-I and ACS-II is originated from the catalyst characterization and control experiments, in which Ni-I and Ni-II catalysts derived from isomorphrous 2D Ni-based MOFs show no catalytic activity on the transformation of FUR under the similar conditions.Download high-res image (119KB)Download full-size image

A highly efficient and selective oxidative condensation–hydrogenation process of renewable furfural with aliphatic alcohols catalyzed by metallic platinum in a one-pot reactor is developed. A series of supported platinum catalysts including Pt/FH, Pt/H, Pt/HT, Pt/Fe3O4, Pt/Al2O3 and Pt/ZrO2 are prepared and employed for the polarization of furfural in ethanol and n-propanol. It is found that, in the presence of Pt/FH and potassium carbonate, 93.9% conversion of furfural and 67.9% selectivity to furan-2-acrolein were obtained via oxidative condensation in the furfural–ethanol–O2 (FEO) system, and 90.1% conversion of furfural and 90% selectivity to 3-(furan-2-yl-)-2-methylacrylaldehyde were obtained via oxidative condensation in the furfural–n-propanol–O2 (FPO) system. Moreover, the oxygen in the FPO system is completely replaced by molecular hydrogen to allow the further conversion of 3-(furan-2-yl-)-2-methylacrylaldehyde, while the catalytic system was kept unchanged. During this process, 87.3% conversion of 3-(furan-2-yl-)-2-methylacrylaldehyde and 73.2% selectivity to 3-(furan-2-yl-)-2-methylpropanol were obtained via a hydrogenation reaction with the Pt/FH catalyst. Moreover, several common bases as promoters were investigated in detail. All the catalysts were characterized by XRD, TEM, SEM, TPD and BET methods to reveal their catalytic nature in the reaction.

The oxidative condensation of furfural with aliphatic alcohols catalyzed by the supported CoxOy–N catalysts is developed in the presence of molecular oxygen. For the oxidative condensation process of furfural, n-propanol and dioxygen, a 75.1% conversion of furfural and 92.8% selectivity of 3-(furan-2-yl-)-2-methylacryaldehyde was obtained when the CoxOy–N@K-10 and cesium carbonate was employed as catalytic system. Moreover, the reaction conditions were optimized and the oxidative condensation of furfural with different aliphatic alcohols was also investigated. The synergistic effect between the CoxOy–N@K-10 and basic additive was considered to be responsible for this cascade process. Furthermore, a possible reaction mechanism is proposed for oxidative condensation of furfural–n-propanol–O2 (FPO) system.Keywords: Biomass conversion; Furfural; Molecular oxygen; n-Propanol; Non-noble metal catalyst; Oxidative condensation

The tunable transformation of renewable furfural with aliphatic alcohols in the presence of O2 is developed. Based on a nano Au catalyst and potassium carbonate, a 91.8% yield of methyl 2-furoate with 98.7% selectivity is obtained via the oxidative esterification in a furfural–methanol–O2 system; while a 91.4% yield of 3-(furan-2-yl-)-2-methylacrylaldehyde with 97.2% selectivity is attained via the oxidative condensation in a furfural–n-propanol–O2 system.

An efficient and selective oxidation of 5-hydroxymethylfurfural (HMF) to produce 2,5-diformyl furan (DFF) has been achieved using a cheap copper(I) iodate as catalyst in dimethylsulfoxide solvent. The effect of different mediators including N-hydroxyphthalimide, 2,2,6,6-tetramethyl piperidine-1-oxyl radical, 1-hydroxybenzotriazole (HBT) and N-methylmorphilone N-oxide were investigated. It was found that the combination of CuI–HBT favors the generation of DFF in the oxidation. Moreover, the molecular oxygen as the oxidant is superior to tert-butyl hydroperoxide and hydrogen peroxide as oxidant in this catalytic process. For instance, a 93.2% conversion and 99% selectivity for DFF was obtained under 0.3 MPa of O2 at 130 °C for 10 h. The effects of catalyst amount, temperature and solvent were also discussed. Furthermore, a hypothetical reaction mechanism is proposed.

The selective conversion of d-fructose and inulin to produce 5-hydroxymethyl furfural (HMF) is achieved in the presence of a catalytic amount of graphite derivatives such as graphite oxide (GO), reduced graphite oxide (RGO) and sulfated reduced graphite oxide (G-SO3H). As a result, a HMF yield of up to 60.8 % from d-fructose and as much as 58.2 % from inulin was obtained in the presence of GO under suitable conditions. The effects of reaction temperature and the time in the dehydration of d-fructose and inulin are investigated in detail. Then, graphite derivatives are detected by IR and XRD techniques to confirm its structure and property. Moreover, GO was further treated by high temperature and strong base/acid which are respectively named as h-GO and n-GO, and their catalytic performances are increased a little in the d-fructose dehydration. This exhibits that graphite derivatives are a kind of promising metal-free catalysts for the selective conversion of biomass feedstocks.

•A new transition metal-free catalyst system for aerobic oxidation is developed.•The efficient oxidation of alcohols with molecular oxygen is achieved.•The catalytic system is composed of DDQ, NaNO2 and NBS.•76–99% yields of aldehydes are obtained from oxidation of aromatic alcohols.A highly efficient N-bromosuccinimide (NBS)-mediated transition metal-free catalytic system has developed for the efficient aerobic oxidation of aromatic alcohols. Various aromatic alcohols are successfully oxidized to the corresponding aldehydes or ketones under mild condition. For instance, benzyl alcohol is oxidized to benzaldehyde with 99% conversion in 94.5% selectivity with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)–NaNO2–NBS system under 0.3 MPa of O2 at 90 °C for 2 h. The effects of reaction time, catalyst amount and solvents are investigated in detail, and a possible reaction mechanism is proposed.

An efficient and tin-catalyzed production of 5-hydroxymethyl furfural (5-HMF) from carbohydrates is reported. The efficient conversion of glucose has been investigated using the combination of SnCl4 and different quaternary ammonium salts. It was found that tetrabutyl ammonium bromide (TBAB) was able to efficiently promote conversion of glucose to 5-HMF in the presence of SnCl4. For instance, a 69.1% yield of 5-HMF was obtained with SnCl4–tetrabutyl ammonium bromide (SnCl4–TBAB) system in DMSO for 2 h at 100 °C in air. The effects of catalyst amount, reaction time, and reaction temperature were investigated in detail. Furthermore, the SnCl4–TBAB was also employed to the conversion of fructose, sucrose, inulin, starch, and cellulose. The competitive results were obtained under mild conditions.Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Efficient production of 5-hydroxymethylfurfural from carbohydrates is achieved. ► A 69.1% yield of 5-hydroxymethylfurfural is obtained from glucose. ► The effects of reaction time, temperature, and catalyst amount are investigated. ► Conversion of sucrose, inulin, and starch is studied with SnCl4–TBAB system.

The highly efficient and selective production of 5-hydroxymethylfurfural (HMF) from sucrose has been achieved in the presence of metal chlorides and ammonium halides under mild conditions. Notably, an 87% yield of HMF from sucrose was obtained with a catalyst system composed of CrCl3 and NH4Br at 100 °C for 1.0 h in N,N-dimethylacetamide (DMAc) solvent. The effect of the reaction temperature and time was investigated in detail, and a possible mechanism for this catalytic process has been proposed. In addition, NH4Br is an effective promoter in the conversion of glucose and fructose to HMF.Graphical abstractHighlights► Efficient production of 5-hydroxymethylfurfural from sucrose is achieved. ► The catalytic system includes ammonium bromide and chromium chloride. ► An 87% yield of 5-hydroxymethylfurfural has been obtained. ► Possible reaction mechanism is proposed.

The influences of Lewis acids and substituents on carbonyl-ene reactions between formaldehydes and propenes have been studied using density functional theory (DFT) calculations. Twelve different Lewis acids including AlCl3, MeAlCl2, Me2AlCl, Me3Al, Al(OMe)3, BF3, CoCl3, SnCl4, TiCl4, YCl3, ZnCl2 and ZrCl4 were chosen as promoters, and CF3, COOCH3, NO2, F, Cl, Br, Ph, CH2CH-, t-Bu, CH3 and OCH3 groups were employed as monosubstituents for formaldehyde or propene. The DFT results show that in the presence of a Lewis acid, the activation energy for carbonyl-ene reactions greatly decreases with the endergonic process becoming exergonic. The frontier molecular orbital energies were also investigated to evaluate the influence of Lewis acids, and AlCl3 was found to be the most efficient for the carbonyl-ene reaction of formaldehyde with propene. In addition, it was found that the electronic, conjugative and steric effects of the substituent have significant influence on the activation and free energy changes for the carbonyl-ene reaction. Moreover, the structures of the transition states and the corresponding bond lengths have been discussed. It is found that the substituent effects are quite different from those of the Diels–Alder reaction.

A highly efficient and selective oxidative condensation–hydrogenation process of renewable furfural with aliphatic alcohols catalyzed by metallic platinum in a one-pot reactor is developed. A series of supported platinum catalysts including Pt/FH, Pt/H, Pt/HT, Pt/Fe3O4, Pt/Al2O3 and Pt/ZrO2 are prepared and employed for the polarization of furfural in ethanol and n-propanol. It is found that, in the presence of Pt/FH and potassium carbonate, 93.9% conversion of furfural and 67.9% selectivity to furan-2-acrolein were obtained via oxidative condensation in the furfural–ethanol–O2 (FEO) system, and 90.1% conversion of furfural and 90% selectivity to 3-(furan-2-yl-)-2-methylacrylaldehyde were obtained via oxidative condensation in the furfural–n-propanol–O2 (FPO) system. Moreover, the oxygen in the FPO system is completely replaced by molecular hydrogen to allow the further conversion of 3-(furan-2-yl-)-2-methylacrylaldehyde, while the catalytic system was kept unchanged. During this process, 87.3% conversion of 3-(furan-2-yl-)-2-methylacrylaldehyde and 73.2% selectivity to 3-(furan-2-yl-)-2-methylpropanol were obtained via a hydrogenation reaction with the Pt/FH catalyst. Moreover, several common bases as promoters were investigated in detail. All the catalysts were characterized by XRD, TEM, SEM, TPD and BET methods to reveal their catalytic nature in the reaction.

The tunable transformation of renewable furfural with aliphatic alcohols in the presence of O2 is developed. Based on a nano Au catalyst and potassium carbonate, a 91.8% yield of methyl 2-furoate with 98.7% selectivity is obtained via the oxidative esterification in a furfural–methanol–O2 system; while a 91.4% yield of 3-(furan-2-yl-)-2-methylacrylaldehyde with 97.2% selectivity is attained via the oxidative condensation in a furfural–n-propanol–O2 system.