Guoqing Yuan

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.

Temperature-dependent fatigue behaviors of ferroelectric Pb(Zr0.52Ti0.48)O3 and Pb0.75La0.25TiO3 thin films

The polarization switching fatigue of ABO(3)-perovskite ferroelectric thin-film Pb(Zr0.52Ti0.48)O-3 (PZT) prepared by metalorganic decomposition (MOD) and Pb0.75La0.25TiO3 (PLT) prepared by pulsed laser deposition (PLD), are investigated. The temperature as a degree of freedom is employed to modulate the switching fatigue and unveil the roles of oxygen vacancies associated with polarization switching. It is confirmed that the polarization fatigue is dominated by the long-range diffusion of oxygen vacancies, leading to a superior fatigue resistance at low temperature. More importantly, it is revealed that although PLD-prepared PLT films have a higher density of oxygen vacancies than MOD-prepared PZT films, the evaluated barrier for oxygen diffusion in PLD-prepared PLT films is similar to 1.3 eV, larger than similar to 1.0 eV, the barrier in MOD-prepared PZT films, responsible for a weaker fatigue behavior in PLD-prepared PLT films. (c) 2005 American Institute of Physics.

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.

A novel supported catalyst for the carbonylation of methanol

Abstract Porous carbon beads (Ys) prepared from poly(vinylidene chloride) are used as Rh supports for the carbonylation of methanol. TEM and STM images show that uniform pores spread over their surfaces. The optimum temperature for the pyrolysis is 1000°C. The special support has a specific surface area of 1000 m 2 /g with high mechanical strength and thermal stability. The average diameter of pore is in the range of 0.8–1.2 nm suitable for the fine spreading of Rh atoms. XPS spectra indicated that covalent bond is formed between carbon and rhodium in the catalyst, which makes the loss of rhodium become quite little. Catalytic carbonylation results show that the activity and selectivity of this catalyst very excellent. The influence of the external and internal diffusion on the methanol carbonylation was detected. The effect of varying the temperature, concentration of CH 3 I, content of Rh, initial partial pressure of CO and added acetic acid was examined.

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.