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Mixed oxide (ZnAlOx) supported heterogeneous Ni nanoparticle catalysts (Ni/ZnAlOx-600) for the direct synthesis of mono-N-methylamines from amines and methanol.

A superior carbocatalyst ultrahigh N-doped graphene (NG) was prepared by a novel self-sacrificial templating method of one-step annealing vitamin B9. The NG catalyst with pyrolysis temperature of 800 oC (abbreviated VB9-NG-800) has an ultrahigh nitrogen content of 13.5 wt.% and demonstrated the highest activity for the oxidation of bio-based alcohols and terpenes with molecular oxygen without any additives. Systematic characterizations and quantum-chemical calculations further manifested that high contents of graphitic N and pyridinic N species in VB9-NG-800 promoted the generation of •O2− active species from molecular oxygen effortlessly, resulting in excellent catalytic performance for aerobic oxidation.

N-heteroarenes represents one of the most important chemicals in pharmaceuticals and other bio-active molecules, which can be easily accessed from the oxidation of N-heterocycles over metal catalysts. Herein, the metal-free oxidative dehydrogenation of N-heterocycles into N-heteroarenes was developed using molecular oxygen as the terminal oxidant. The nitrogen-doped carbon materials were facilely prepared via the simple pyrolysis process using biomass (carboxymethyl cellulose sodium) and dicyandiamide as the carbon and nitrogen source, respectively, and they were discovered to be robust for the oxidative dehydrogenation of N-heterocycles into N-heteroarenes under mild conditions (80 °C under 1 bar O

Furfural is regarded as one of the most promising bio-based feedstocks in the bio-refinery industry. Selective hydrogenation of the carbonyl bond in furfural plays a vital role in its conversion to downstream products. Electrochemical hydrogenation (ECH) method provides a green and sustainable way for this reaction. Yet, it still suffers from harsh pH conditions and low selectivity for highly reduced products, such as 2-methylfuran. In this study, high faradaic efficiencies of over 90% for furfuryl alcohol and 60% for 2-methylfuran were obtained in a near-neutral environment (pH = 5) at −0.75 V and −0.90 V vs. the reversible hydrogen electrode, respectively. The key to this success is the integration of single atom copper active sites and the oxophilic phosphorus dopants in a single catalyst. Single atom Cu sites are found to be the active centers for this reaction and decreasing the size of Cu sites to a single atom enhances the efficiencies of the ECH reactions by suppressing the competing hydrogen evolution reaction. Phosphorus doping facilitates furfural hydrogenation to 2-methylfuran via a sequential two-step reduction process. This study opens up possibilities for the selective electrochemical hydrogenation of furfural to 2-methylfuran under mild conditions.

There has been a great deal of attention to the development of heterogeneous non-noble metal catalysts for the selective and mild hydrogenation of nitro compounds into primary amines. Herein, a biomass-derived carbon material supported Ni catalyst (Ni/C) was facilely prepared by a one-pot pyrolysis process, and the as-prepared Ni/C catalyst demonstrated a high catalytic activity for the hydrogenation of nitro compounds into primary amines at room temperature. The Ni/C catalyst not only demonstrated a high catalytic activity but also showed a good tolerance to other functional groups. Structurally diverse primary amines were achieved in yields from 92% to 99% within a few hours at room temperature under 5 bar H2. Furthermore, the Ni/C catalyst showed good reusability without the loss of its activity.

The development of new heterogeneous non-noble catalytic systems for the selective hydrogenation of nitriles into primary amines is a challenging task. In this study, a mesoporous Al2O3 supported Ni catalyst (denoted as Ni/Al2O3-600, where 600 represents the reduction temperature) demonstrated a high catalytic activity for the hydrogenation of nitriles under mild conditions (60–80 °C and 2.5 bar H2) with ammonia as the additive. This catalytic system has a wide substrate range and the Ni/Al2O3 catalyst demonstrated a good tolerance to other functional groups, which was possibly due to its high catalytic activity under mild conditions. A plausible reaction pathway was proposed for the hydrogenation of nitriles into primary amines, and it was found that ammonia played a great role in the enhancement of the selectivity of primary amines by the inhibition of the side reaction to generate secondary amines. In addition, the Ni/Al2O3-600 catalyst could be reused five times without activity loss through convenient magnetic recovery.

Nitrogen-doped carbon-supported cobalt–molybdenum bimetallic catalysts (abbreviated as Co–Mo/NC) are active for the hydrodeoxygenation of sulfoxides to sulfides under mild conditions (25–80 °C and 10 bar H2), which represents the first example of the use of heterogeneous non-noble metal catalysts for this transformation. MoO3 with Lewis acid sites assists the hydrodeoxygenation of sulfoxides into sulfides by hydrogen over cobalt nanoparticles.

5-Formyl-2-furancarboxylic acid (FFCA) is an important bio-blocks material, which has promising applications in synthesis, chemical intermediates, drugs, etc. However, the selective oxidation of 5-hydroxymethylfurfural (HMF) into FFCA seems very difficult, which has been rarely studied. In this study, we have developed a new method for the selective oxidation of HMF to FFCA over a Fe-Anderson type catalyst of Na3H6FeMo6O24·5H2O (abbreviated as FeMo6). The FeMo6 catalyst was prepared by the recrystallization method and systematically characterized by XRD, UV–vis, FT-IR, TG, ICP-AES, and XPS technologies. Mo5+ species and a large number of surface oxygen species were found to be close-knit associated with catalytic performances. The experiment found that the maximum FFCA yield can be obtained when n-methyl pyrrolidone (NMP) was used as the reaction solvent and the HMF and K2CO3 molar ratio was 0.5. Under the optimal conditions (HMF/ K2CO3/Catalyst = 1/0.5/0.08, T = 100 °C, 8 h), the oxidation of HMF over the FeMo6 catalyst could produce FFCA with a yield of 75% in the solvent of NMP. Most importantly, this catalyst was employed in this reaction under aerobic environment at atmospheric pressure, demonstrating a high catalytic activity.

A heterogeneous Ni catalyst was discovered to be active in the synthesis of secondary cross-imines via hydrogenative coupling of nitriles and amines. The mesoporous Al2O3-supported Ni nanoparticles...

Catalytic oxidative dehydrogenation of N-heterocyclic compounds has been considered to be an important route to access heteroarenes. In this study, a heterogeneous catalyst by the loading of cobalt...

The use of non-noble metal catalysts with high activity is of great importance for organic transformations. Herein, nitrogen-doped carbon supported cobalt catalysts with high surface area up to 981.2 m2/g were prepared via the simple pyrolysis of cobalt coordinated organic polymers with silica as the hard template. The pyrolysis temperature showed a great effect on the structure and properties of the as-prepared catalysts. The Co@NC-800 catalyst with the pyrolysis temperature of 800 °C demonstrated a high activity for the selective reductive amination of carbonyl compounds to primary amines with ammonia and hydrogen. Structurally-diverse primary amines with yields in the range from 81.8% to 100% were attained under the optimal conditions. The Co@NC-800 catalyst could be reused without the loss of its activity. The Co@NC-800 catalyst demonstrated comparable activity as the reported heterogeneous noble metal catalysts.

The development of new strategies for metal-free promoted reactions has recently received great interest from chemists because these processes benefit from the use of inexpensive catalysts and from avoidance of contamination of the desired products by the metal catalysts. In this study, a method for HNO3-promoted oxidation of biomass-derived 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF) was developed in the presence of nitrogen-doped carbon materials using molecular oxygen as the terminal oxidant under mild reaction conditions. The catalytic activity of the nitrogen-doped carbon materials was discovered to greatly increase with increasing pyrolysis temperature; it also depended on both the type of nitrogen atoms in the catalyst and the surface area of the catalyst. The NC-950 catalyst demonstrated unprecedented catalytic activity towards the oxidation of HMF to DFF. Several reaction parameters, such as the reaction solvent, the reaction temperature, the amount of HNO3, the catalyst loading and the oxygen pressure, have been investigated. The highest DFF yield of 95.1% was attained with full HMF conversion after 14 h at 100 °C under 10 bar oxygen pressure in the presence of a catalytic amount of HNO3. Control experiments indicated that the oxidation of HMF was initially promoted by HNO3, and O2 acted as a secondary oxidant for HNO3 recovery. In particular, the NC-950 catalyst had remarkable reusability without significant losses in its activity and selectivity after six consecutive usages.

The selective oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-diformylfuran (DFF) has attracted much attention in recent years. Cesium-doped manganese dioxide (Cs/MnOx) was prepared by a soft template method, and was found to be active for the selective oxidation of HMF to DFF with molecular oxygen. Various reaction conditions have been investigated, and DFF was attained with a high yield of 94.7% at a HMF conversion of 98.4% at 100 °C and 10 bar O2 in N,N-dimethylformamide. Cs/MnOx demonstrated much higher catalytic activity than un-doped MnOx, suggesting that the introduction of Cs into MnOx plays a crucial role in the oxidation of HMF to DFF. Kinetic studies demonstrated that the oxidation of HMF to DFF depends on both the HMF and oxygen concentration, with the reaction order being 0.44 and 0.53, respectively. Compared with other heterogeneous non-noble metal catalysts, Cs/MnOx demonstrated a much lower activation energy for the oxidation of HMF to DFF. The catalyst can be reused without much loss of catalytic activity, suggesting that the catalyst is highly stable. Furthermore, the direct production of HMF from fructose was also successfully realized by a one-pot reaction strategy via two consecutive steps.

Synthesis of secondary amines direct from the coupling of two aldehydes was first reported in the presence of NH3 and H2 molecules. A magnetic material supported palladium catalyst (γ-Fe2O3@HAP-Pd) was found to be active for this transformation at room temperature and atmospheric hydrogen pressure, providing structurally diverse secondary amines with good to excellent yields (70.0–92.3%).

Nitrogen-doped reduced graphene oxide-supported Mn3O4 nanoparticles (N-RGO/Mn3O4) were prepared by solvothermal method and characterized by several physical techniques such as TEM images, XRD, XPS, and N2 adsorption–desorption techniques. The as-made N-RGO/Mn3O4 catalyst was used for the oxidation of vanillyl alcohol to vanillin. Several important reaction parameters were investigated such as reaction solvent, oxygen concentration, reaction temperature, and catalyst loading. N,N-Dimethylformamide was found to be the best solvent, affording both high conversion and vanillin selectivity. 92.5 % conversion of vanillyl alcohol and 91.4 % selectivity of vanillin were achieved after 12 h at 120 °C under oxygen balloon by the use of 40 mg of the N-GO/Mn3O4 catalyst. Kinetic studies revealed that the active energy for the oxidation of vanillyl alcohol to vanillin over N-GO/Mn3O4 catalyst was 39.67 kJ.mol−1. More importantly, the catalyst was stable and could be reused for 6 times without the significant loss of its catalytic activity.

In this study, a new ruthenium catalyst was used for the oxidation of biomass derived 5-hydroxymethylfurfural (HMF) under mild conditions, which was prepared by the exchange of Ru3+ with H+ in the structure of the zirconium phosphate (ZrP). The as-prepared ZrP–Ru catalyst showed high catalytic activity towards the oxidation of HMF, affording 100% of HMF conversion at 130 °C after 12 h under atmospheric oxygen pressure. 2,5-Furandicarboxylic acid (FDCA) and 2,5-diformylfuran (DFF) were detected to be the major oxidation products.

In this study, magnetic γ-Fe2O3@HAP-Mo catalyst was successfully prepared and characterized. The activity of the as prepared γ-Fe2O3@HAP-Mo catalyst was evaluated by the oxidation of 5-hydroxymethylfurfural (HMF) with molecular oxygen. Some important reaction parameters were investigated and it was found that both the solvent and the reaction temperature showed great effect on HMF conversion and products selectivity. The highest HMF conversion of 95.8% was obtained in 4-chlorotoluene at the reaction temperature of 120 °C for 12 h, and the corresponding 2,5-diformylfuran, 2,5-furandicarboxylic acid and 5-hydroxymethyl-2-furancarboxylic acid yields were 67.5, 19.6 and 8.7%, respectively. The γ-Fe2O3@HAP-Mo catalyst could be easily separated from the reaction mixture and reused several times without the loss of its catalytic activity.

In this study, we have developed an effective method for the conversion of carbohydrates into liquid biofuels 5-ethoxymethylfurfural (EMF) over a magnetic solid acid catalyst (Fe 3 O 4 @C SO 3 H). The as-prepared magnetic Fe 3 O 4 @C SO 3 H catalyst showed high catalytic activity toward the synthesis of EMF from carbohydrates. The etherification of 5-hydroxymethylfurfural (HMF) with ethanol over Fe 3 O 4 @C SO 3 H catalyst produced EMF with a high yield of 88.4%. The Fe 3 O 4 @C SO 3 H catalyst also showed high activity toward the one-pot conversion of fructose based carbohydrates into EMF. EMF was obtained in a yield of 67.8% from fructose, and that was 58.4% from inulin. The Fe 3 O 4 @C SO 3 H catalyst could be easily collected by an external magnet and reused for several times without the significant loss of its catalytic activity.

Magnetic γ-Fe2 O3 nanocrystallites encapsulated by hydroxyapatite (HAP), HAP@γ-Fe2 O3 , were prepared followed by cation exchange of Ca(2+) on the external HAP surface with Ru(3+) to give the γ-Fe2 O3 @HAP-Ru catalyst. The structure of the as-prepared catalyst was characterized, and its catalytic activity was studied in the aerobic oxidation of 5-hydroxymethylfurfural (HMF). γ-Fe2 O3 @HAP-Ru showed a high catalytic activity for the aerobic oxidation of HMF into 2,5-diformylfuran (DFF). A high DFF yield of 89.1 % with an HMF conversion of 100% was obtained after 4 h at 90 °C. Importantly, the synthesis of DFF from fructose was realized by two consecutive steps. The dehydration of fructose in the presence of a magnetic acid catalyst (Fe3 O4 @SiO2-SO3 H) produced HMF in a yield of 90.1%. Then the Fe3 O4 @SiO2 SO3 H catalyst was removed from the reaction solution with a permanent magnet, and HMF in the resulting solution was further oxidized to DFF with a yield of 79.1% based on fructose. The synthesis of DFF from fructose by two steps avoids the tedious separation of the intermediate HMF, which saves time and energy.