Bingfeng Chen

Integrated Catalytic Process to Directly Convert Furfural to Levulinate Ester with High Selectivity

Levulinic acid is an important platform molecule from biomass-based renewable resources. A sustainable manufacturing process for this chemical and its derivatives is the enabling factor to harness the renewable resource. An integrated catalytic process to directly convert furfural to levulinate ester was developed based on a bifunctional catalyst of Pt nanoparticles supported on a ZrNb binary phosphate solid acid. The hydrogenation of furfural and the following alcoholysis of furfuryl alcohol were performed over this catalyst in a one-pot conversion model. Mesoporous ZrNb binary phosphate was synthesized by a sol-gel method and had a high surface area of 170.1 m(2) g(-1) and a large average pore size of around 8.0 nm. Pt nanoparticles remained in a monodisperse state on the support, and the reaction over Pt/ZrNbPO4 (Pt loading: 2.0 wt%; Zr/Nb, 1:1) gave a very high selectivity to levulinate derivatives (91% in total). The sustainability of this conversion was greatly improved by the process intensification based on the new catalyst, mild reaction conditions, cost abatement in separation and purification, and utilization of green reagents and solvents.

Nanosheets of graphitic carbon nitride as metal-free environmental photocatalysts

Nanosheets of graphitic carbon nitride were prepared through direct heat treatment of guanidinium chloride at 450–600 °C in air. The resultant materials had a surface area of 109.9 m2 g−1 and their physicochemical properties were closely related to the condensation temperature. Decomposition of rhodamine (RhB) in aqueous solution was selected as the model reaction to investigate the photocatalytic performance of nanostructured graphitic carbon nitride. The sample with higher surface area exhibited better optical properties and had enhanced photocatalytic activity. These findings suggest that graphitic carbon nitride prepared from guanidinium chloride will be promising for use in pollutants degradation and solar energy utilization.

Cycloaddition of CO2 and epoxide catalyzed by amino- and hydroxyl-rich graphitic carbon nitride

Graphitic carbon nitride (g-C3N4) shows great application potential in the activation of CO2 due to its basic surface functionalities and highly specific electronic properties. Herein, to improve its catalytic performance, g-C3N4 was activated by protonation using H2SO4. The texture, surface chemistry and electronic properties of the as-prepared g-C3N4 were then studied. The synthesis of cyclic carbonate from the cycloaddition of CO2 and epoxide was selected as a model reaction to investigate the catalytic performance. The protonated g-C3N4 exhibited a much higher catalytic activity than the pristine g-C3N4. The generation of terminal amino and hydroxyl groups due to the hydrolysis of g-C3N4 under acidic conditions as well as the higher specific surface area are responsible for the enhanced catalytic performance.

Porous and low-defected graphitic carbon nitride nanotubes for efficient hydrogen evolution under visible light irradiation

Porous and low-defect graphitic carbon nitride (g-C3N4) nanotubes were fabricated through heating precursors synthesized by recrystallization from H2SO4/methanol. The textural and chemical structures of the as-prepared samples were well studied. Recrystallization and subsequent heating result in g-C3N4 nanotubes with developed porosity and high specific surface area. Unexpectedly, the nanotubes exhibit much ordered tri-s-triazine conjugated network and fewer defects. Compared to bulk g-C3N4 prepared by direct heating melamine, the nanotubes demonstrate enhanced photocatalytic activity for hydrogen evolution under visible light irradiation. Besides the improved textural and chemical structures, the optimized optical and electronic properties are contributed to the enhanced photocatalytic performance.

Recyclable and Selective Nitroarene Hydrogenation Catalysts Based on Carbon-Coated Cobalt Oxide Nanoparticles

Co/CoO nanoparticles coated with graphene layers (Co/CoO@Carbon) have been developed through direct heating treatment of cobalt oxide precursors incipiently deposited over nanographite materials. Cobalt oxides are partially reduced to active zero‐valent metal species and the simultaneous formation of carbon layers over the nanoparticles protects them from oxidation and deactivation. This nanocatalyst performs excellently in chemoselective hydrogenation of some challenging nitroarenes with reducible functionalities to the corresponding anilines. The catalyst is kept in active and selective performance in a ten‐run recycling test.

Hydrogen from Water over Openly-Structured Graphitic Carbon Nitride Polymer through Photocatalysis.

Openly-structured g-C3 N4 microspheres (CNMS) are developed through a well-controlled strategy. These materials have unique features of open 3 D structure, ordered hierarchical porosity, and improved optical and electronic properties. Hydrogen evolution from water is performed under a 300 W Xe lamp with a cut-off filter (λ>420 nm) and Pt nanoparticles are used as the co-catalyst (3.0 wt%). The catalyst prepared at 600 °C (CNMS-600) has a hydrogen evolution rate (HER) of 392 μmol h(-1) (apparent quantum yield, AQY=6.3%) at 420 nm. This value is higher than that of g-C3 N4 nanosheets prepared through thermal oxidation, liquid exfoliation, or chemical exfoliation. The HER value is only 27 μmol h(-1) (AQY=0.43%) at 420 nm for bulk g-C3 N4 from melamine. The evolution of openly-structured CNMS was investigated by TEM, FTIR, and XRD. The improved optical and electronic properties were demonstrated through UV/Vis absorption spectra, valence-band X-ray photoelectron spectroscopy, photoluminescence spectroscopy, electron paramagnetic resonance spectroscopy, and electrochemical impedance spectroscopy.

Sustainable catalysts for methanol carbonylation

Methanol carbonylation is the most important process for manufacturing C2 molecules from methanol. The present industrial carbonylation has been proven to be the most successful process on economical grounds. However, there is a request to develop more sustainable and ‘green’ processes to overcome the inherent drawbacks. Well-designed cross-linked copolymers were prepared and used as support for the simultaneous immobilization of rhodium and iodide species. The resulting catalyst was proven to be highly active in CH3I-free methanol carbonylation and methyl acetate was the main product. Approximately 90% of methanol was converted after a two-hour reaction time at 120 °C under a CO pressure of 3.0 MPa. The immobilization strategy of the active species works efficiently and the present methanol carbonylation catalyst shows good recyclability. After regenerating the catalyst twice over a fifteen-batches test, the catalyst keeps an acceptable activity. The process based on the present catalyst is evidently a promising sustainable methanol carbonylation.

Nanoporous photocatalysts developed through heat-driven stacking of graphitic carbon nitride nanosheets

Nanoporous graphitic carbon nitride was prepared through direct heat treatment of guanidinium cyanurate at 550–600 °C in an air atmosphere. The BET surface area of the resulting materials can reach 200 m2 g−1. High porosity was developed through a heat-driven stacking of g-C3N4 nanosheets. The mechanism was revealed in detail through TEM and N2 adsorption measurements. Large-size g-C3N4 nanosheets are formed at 550 °C and stacked in a state similar to randomly creased paper slips. Further increase of treatment temperature to 600 °C results in curling and fragmentation of g-C3N4 nanosheets, which build up a highly porous matrix. Nanoporous graphitic carbon nitride with higher surface area exhibits better optical properties and has enhanced photocatalytic activity. The nanoporous g-C3N4 shows high photocatalytic activity for the decomposition of rhodamine (RhB) in an aqueous solution.

Sustainable catalytic oxidation of alcohols over the interface between air and water

Alcohols are oxidized to aldehydes or ketones in water by directly using air as the oxidant. The catalytic conversions are based on a hybrid nanocatalyst with monodispersed Au nanoparticles embedded in a polyoxometalate self-assembly matrix. The oxidation processes exhibit excellent activity and selectivity.

Highly Stable, Recyclable Copper Nanoparticles as Catalysts for the Formation of CN Bonds

There is a great impetus for the development of “green” catalytic techniques, that is to say, catalysts that are environmentally friendly and designed for easy separation from the reaction system with the ability to be recycled without loss of catalytic efficiency. To achieve this goal, catalyst development needs to break the strict borderline between heterogeneous catalysis and homogeneous catalysis. Metal nanoparticles provide new research horizons for this goal. Metal nanoparticles with high catalytic activity exist as nanoscale clusters containing between ten to several thousands of metal atoms, and are up to a few nanometers in diameter. They can mimic the metal surface activation and catalysis of heterogeneous catalysts. The high fraction of the metal atoms exposed at the surface, combined with electron quantum-confinement in very small metal particles, bestows attractive catalytic properties. Metal nanoparticles can also be handled as molecular compounds, which are soluble in many classic solvents and can be subsequently applied as catalysts in homogeneous systems. Through fixation of catalysts onto heterogeneous supports, homogeneous systems can be heterogenized. Metal nanoparticles are the bridge between heterogeneous catalysis and homogeneous catalysis, and, as such, their preparation, stabilization, and catalytic application are areas of significant attention. There are many excellent reviews covering this topic. However, many of the fundamental issues with the development of practical, recyclable colloidal catalysis are not fully appreciated. In this work, stable, recyclable colloidal Cu nanoparticles (CuNPs) were developed for use as catalysts, and the C N formation reaction was selected as the model reaction to test their activity and recyclability. 4-Dimethylaminopryidine (DMAP) is a good stabilizing ligand for metal nanoparticles and can transfer metal nanoparticles from organic phase to aqueous solution. DMAP-stabilized Cu nanoparticles (DMAPCuNPs) were prepared through a well-designed method. These materials are soluble in polar solvents such DMF, DMA (N,N-dimethylacetamide), and DMSO and can be easily separated by adding ether or toluene into the solution. DMAP-CuNPs catalyze the reaction as a homogeneous system and can be separated and recycled as in heterogeneous catalysis. Cu-catalyzed Ullmann coupling is a key reaction in the formation of carbon-heteroatom bonds in organic synthesis. Numerous efficient homogeneous Cu-catalyzed C N coupling reactions have been developed, but few recyclable catalysts for C N coupling under heterogeneous conditions have been reported. Majoral et al. reported an iminopyridine ligand grafted onto phosphorus dendrimers for supporting Cu, which catalyzed the coupling of aryl iodides or vinyl bromides with pyrazole at 25–80 8C. Ligands or Cu complexes supported over silica, the apatite support, and magnetic nanoparticles have been designed for the coupling of N-heterocycles with aryl halides. Cu or Cu2O nanoparticles are another type of active heterogeneous catalyst for the C N coupling reaction. In our previous work, nitrogen-enriched polymer-supported Cu nanoparticles were proven to be active and recyclable catalysts for arylation of N-heterocycles. In this investigation, it is demonstrated that DMAP-CuNPs are highly active and recyclable catalysts for C N Ullmann coupling reaction and some complex molecules were synthesized over this recyclable colloidal catalyst. DMAP-CuNPs were prepared through controlled decomposition of a DMAP-Cu(acac)2-carbohydrazide complex (acac = acetylacetonate) in anhydrous ethanol. The solvent was removed by evaporation and the dried DMAP-CuNPs can be stored in dry Ar for several months without deactivation. Figure 1 a is a TEM image of fresh DMAP-CuNPs; they remain monodisperse and of regular spherical shape and have a narrow size distribution (mainly 4–7 nm in diameter) (Figure 1 b). The chemical states of the CuNPs were measured by X-ray photoelectron spectroscopy (XPS). The binding energy of Cu 2p3/2 is 931.6 eV, which is about 0.8 eV lower than that of zero-valent bulk copper. This is caused by the strong electron donor effect of DMAP, which stabilizes the CuNPs. The difference between the two spin-orbit splitting peaks (Cu 2p3/2, Cu 2p1/2) is 19.8 eV, which is indexed to zero-valent copper species (Figure 1 c). The coupling reactions of hexylamine and imidazole with aryl halide were selected as model reactions for testing the catalytic activity of DMAP-CuNPs. The reactions were carried out in DMF at 100 8C for 6 h, with CsCO3 as a base. DMAPCuNPs show mild catalytic activity for phenyl chloride and very high activity for phenyl bromide and iodide (Figure 2 a). There is a slight difference in catalytic coupling activity between hexylamine and imidazole. Recyclable colloidal DMAP-CuNPs exhibit catalytic activity nearly equal to homogeneous Cu catalysts and have marked advantages over other heterogeneous Cu catalysts (Figure 2 b). The recyclability of DMAP-CuNPs was investigated through the coupling reaction between imidazole and phenyl bromide, [a] B. Chen, Dr. F. Li, Z. Huang, F. Xue, T. Lu, Y. Yuan, Prof. G. Yuan Beijing National Laboratory of Molecular Science Laboratory of New Materials, Institute of Chemistry Chinese Academy of Sciences Beijing, 100190 (P. R. China) Fax: (+ 86) 10-62559373 E-mail : lifb@iccas.ac.cn yuangq@iccas.ac.cn [b] B. Chen, Z. Huang, F. Xue, T. Lu, Y. Yuan Graduate University of Chinese Academy of Sciences Beijing, 100049 (P. R. China) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cctc.201200312.