Minghui Tan

Pt Nanocatalysts Supported on Reduced Graphene Oxide for Selective Conversion of Cellulose or Cellobiose to Sorbitol

Pt nanocatalysts loaded on reduced graphene oxide (Pt/RGO) were prepared by means of a convenient microwave-assisted reduction approach with ethylene glycol as reductant. The conversion of cellulose or cellobiose into sorbitol was used as an application reaction to investigate their catalytic performance. Various metal nanocatalysts loaded on RGO were compared and RGO-supported Pt exhibited the highest catalytic activity with 91.5 % of sorbitol yield from cellobiose. The catalytic performances of Pt nanocatalysts supported on different carbon materials or on silica support were also compared. The results showed that RGO was the best catalyst support, and the yield of sorbitol was as high as 91.5 % from cellobiose and 58.9 % from cellulose, respectively. The improvement of catalytic activity was attributed to the appropriate Pt particle size and hydrogen spillover effect of Pt/RGO catalyst. Interestingly, the size and dispersion of supported Pt particles could be easily regulated by convenient adjustment of the microwave heating temperature. The catalytic performance was found to initially increase and then decrease with increasing particle size. The optimum Pt particle size was 3.6 nm. These findings may offer useful guidelines for designing novel catalysts with beneficial catalytic performance for biomass conversion.

Facile hydrothermal synthesis of SnO2/C microspheres and double layered core–shell SnO2 microspheres as anode materials for Li-ion secondary batteries

SnO2/C microspheres and double layered core–shell SnO2 microspheres have been synthesized by a facile hydrothermal method with a post heat-treatment. The soluble starch used as carbon source and the mass ratio of starch to SnCl4·5H2O play key roles in the formation of SnO2/C microspheres, and the hydrothermal synthesis mechanism of SnO2/C microspheres has been proposed. SnO2/C-1.0 microspheres (the mass ratio of soluble starch to SnCl4·5H2O is 1:1) with good spherical shape and 34.91 wt% of SnO2 exhibit superior rate capability and cyclic stability, while double layered core–shell SnO2 microspheres show improved electrochemical performance compared to SnO2 particles. The electrode based on SnO2/C-1.0 microspheres delivers a reversible discharge capacity of 568 mA h g−1 at a constant current density of 100 mA g−1 in the second cycle, and 379 mA h g−1 (67% retention) is retained after the 50th cycle, suggesting SnO2/C microspheres are promising candidates for energy storage.

Monodispersed Hollow SO3H-Functionalized Carbon/Silica as Efficient Solid Acid Catalyst for Esterification of Oleic Acid

SO3H-functionalized monodispersed hollow carbon/silica spheres (HS/C-SO3H) with primary mesopores were prepared with polystyrene as a template and p-toluenesulfonic acid (TsOH) as a carbon precursor and -SO3H source simultaneously. The physical and chemical properties of HS/C-SO3H were characterized by N2 adsorption, TEM, SEM, XPS, XRD, Raman spectrum, NH3-TPD, element analysis and acid-base titration techniques. As a solid acid catalyst, HS/C-SO3H shows excellent performance in the esterification of oleic acid with methanol, which is a crucial reaction in biodiesel production. The well-defined hollow architecture and enhanced active sites accessibility of HS/C-SO3H guarantee the highest catalytic performance compared with the catalysts prepared by activation of TsOH deposited on the ordered mesoporous silicas SBA-15 and MCM-41. At the optimized conditions, high conversion (96.9%) was achieved and no distinct activity drop was observed after 5 recycles. This synthesis strategy will provide a highly effective solid acid catalyst for green chemical processes.

Active and regioselective rhodium catalyst supported on reduced graphene oxide for 1-hexene hydroformylation

Alkene hydroformylation with syngas (CO + H2) to produce aldehydes is one of the most important chemical reactions. However, designing heterogeneous catalysts to realize comparable performance with mature homogeneous catalysts is challenging. In this report, a reduced graphene oxide (RGO) supported rhodium nanoparticle (Rh/RGO) catalyst was successfully prepared via a one-pot liquid-phase reduction method and first applied in 1-hexene hydroformylation. 1-Hexene hydroformylation reaction under different reaction conditions with this Rh/RGO catalyst was investigated in detail. Low reaction temperature and short reaction time effectively enhanced the n/i (normal to iso) ratio of heptanal in the products. The catalytic performance of the Rh/RGO catalyst was also compared with those of Rh supported on other carbon materials, including activated carbon and carbon nanotubes (Rh/AC and Rh/CNTs). The results showed that the Rh/RGO catalyst exhibited the highest 1-hexene conversion and the largest n/i ratio of 4.0 among the tested catalysts. The special 2D nanosheet structure of the Rh/RGO catalyst, rather than the 3D porous and 1D nanotube structures of Rh/AC and Rh/CNTs, respectively, principally contributed to its excellent catalytic performance. These findings disclosed that reduced graphene oxide could be a promising catalyst support for designing heterogeneous hydroformylation catalysts.

Rapid oxidation and immobilization of arsenic by contact glow discharge plasma in acidic solution.

Arsenic is a priority pollutant in aquatic ecosystem and therefore the remediation of arsenic-bearing wastewater is an important environmental issue. This study unprecedentedly reported simultaneous oxidation of As(III) and immobilization of arsenic can be achieved using contact glow discharge process (CGDP). CGDP with thinner anodic wire and higher energy input were beneficial for higher As(V) production efficiency. Adding Fe(II) in CGDP system significantly enhanced the oxidation rate of As(III) due to the generations of additional OH and Fe(IV) species, accompanied with which arsenic can be simultaneously immobilized in one process. Arsenic immobilization can be favorably obtained at solution pH in the range of 4.0-6.0 and Fe(II) concentration from 250 to 1000 μM. The presence of organics (i.e., oxalic acid, ethanol and phenol) retarded the arsenic immobilization by scavenging OH or complexing Fe(III) in aqueous solution. On the basis of these results, a mechanism was proposed that the formed ionic As(V) rapidly coprecipitated with Fe(III) ions or was adsorbed on the ferric oxyhydroxides with the formation of amorphous ferric arsenate-bearing ferric oxyhydroxides. This CGDP-Fenton system was of great interest for engineered systems concerned with the remediation of arsenic containing wastewater.

Designing auto-reduced Cu@CNTs catalysts to realize the precisely selective hydrogenation of dimethyl oxalate

An autoreduced catalyst that comprised Cu nanoparticles encapsulated inside the nanochannels of carbon nanotubes (Cu@CNTs) was designed and prepared. As a result of the interaction of Cu species with the electron‐deficient interior surface of the CNTs, calcination could realize the autoreduction of copper oxide directly with CNTs as the reductant. In the hydrogenation of dimethyl oxalate (DMO), the autoreduced Cu@CNTs catalyst, which did not need to be prereduced, exhibited an excellent catalytic activity, high target product selectivity, and high catalytic efficiency. Furthermore, the effect of the calcination temperature on the autoreduction degree of Cu@CNTs and the product selectivity in DMO hydrogenation were investigated in detail. The results showed that the autoreduction degree could be tuned easily by changing the calcination temperature, and the highest selectivity of ethanol could be obtained over the catalyst calcined at 500 °C. The findings obtained will inspire the development of other autoreduced catalysts, the reduction degree and catalytic performance of which can be tuned as desired.

Preparation and modification of high performance porous carbons from petroleum coke for use as supercapacitor electrodes

Abstract As a byproduct of oil refining, petroleum coke with a high carbon content (about 90 wt%) has been shown to be a good raw material for porous carbons (PCs). PCs with high specific surface areas were derived from petroleum coke by KOH activation. The effect of KOH/coke mass ratio on the pore structure of the PCs and their electrochemical performance as electrodes of electric double layer capacitors were investigated. Results showed that the specific surface area and pore size distribution of the PCs could be efficiently controlled by the KOH/coke ratio. The pore sizes of the PCs increase with increasing KOH/coke ratio, and the largest specific surface area was as high as 2964 m 2 ·g −1 . A PC-5 electrode prepared with a KOH/coke ratio of 5:1 has a high specific surface area of 2 842 m 2 ·g −1 and mesoporosity of 67.0 %, and has the largest specific capacitance at all investigated current densities among the PCs examined. This is ascribed to its high specific surface area and high mesoporosity. Hydrothermal modification of PC-3 (KOH/coke ratio at 3:1) in ammonia at 200 o C increases its specific capacitance, especially at high discharge current densities. This improved electrochemical performance can be attributed to nitrogen-doping that occurs during the process, and this can induce pseudo-capacitance and improve the hydrophilicity of the PC electrode to the electrolyte. KOH activation combined with ammonia hydrothermal modification is a simple yet efficient approach to prepare cost-effective PCs for supercapacitors with excellent electrochemical performance.