Platinum supported on reduced graphene oxide as a catalyst for hydrogenation of nitroarenes

Reduced graphene oxide (RGO)-supported platinum (Pt) catalyst was prepared by simple ethylene glycol (EG) reduction and used for hydrogenation of nitroarenes. Characterizations showed that EG as a reductant exhibited more advantages than the widely used hydrazine hydrate to fabricate monodispersed, small sized Pt nanoparticles on the surface of RGO. The yield of aniline over the Pt/RGO-_EG catalyst reached 70.2 mol-_AN/(mol-_Pt min) at 0 ^oC, which is 12.5 and 19.5 times higher than that of multi-walled carbon nanotube- and active carbon-supported Pt catalysts, respectively. When the reaction temperature was increased to 20 ^oC, the catalytic activity of Pt/RGO-_EG jumped to 1138.3 mol-_AN/(mol-_Pt min), and it was also extremely active for the hydrogenation of a series of nitroarenes. The unique catalytic activity of Pt/RGO-_EG is not only related to the well dispersed Pt clusters on the RGO sheets but also the well dispersion of Pt/RGO-_EG in the reaction mixture.     

Selective hydrogenation of cinnamaldehyde over reduced graphene oxide supported Pt catalyst

Highly dispersed platinum nanoparticles (NPs) were fabricated on the surface of few-layered reduced graphene oxide (Pt/RGO) via direct ethylene glycol reduction of PtCl₆^2 − in aqueous solution. This well-defined Pt/RGO catalyst was highly selective and active for the hydrogenation of cinnamaldehyde (CAL) to corresponding cinnamyl alcohol (COL) under mild conditions. It was found that the selectivity of COL remained 85.3% at 97.8% CAL conversion in ethanol. These results could be ascribed to the well dispersed Pt NPs on RGO sheets, well dispersion of Pt/RGO in ethanol and ethanol can inhibit the generation of acetals.     

POSS supported C2-symmetric bisprolinamide as a recyclable chiral catalyst for asymmetric Aldol reaction

POSS supported prolinamide-type catalysts were synthesized and used to catalyze asymmetric Aldol reactions between unmodified ketones and aldehydes. Immobilization of the prolinamide-type catalysts onto POSS resulted in good yields and improved diastereoselectivity as well as enantioselectivity. The POSS-supported catalysts were recycled simply by precipitation and filtration, and could be reused in five consecutive cycles without losing its effectiveness.     

Developing chiral ligands for asymmetric hydrogenation

This Account outlines our efforts in ligand development for asymmetric hydrogenation. The successful development of three classes of ligands is presented, including (1) ligands with phosphocyclic motifs, (2) ligands with atropisomeric backbones, and (3) bisphosphine ligands inspired by the structure of 2,3- O-isopropylidene-2,3-dihydroxyl-1,4-bis(diphenylphosphino)butane (DIOP). With this large ligand toolbox, we have prepared many pharmaceutically valuable chiral products efficiently.     

水热合成rGO负载的MoS2催化剂及其催化蒽加氢性能

采用水热法制备了一系列还原氧化石墨烯（rGO）负载的MoS₂催化剂（MoS₂/rGO）。通过SEM、XRD、EDX、拉曼光谱、HRTEM等手段表征了不同钼源制备的MoS₂/rGO催化剂中MoS₂的堆积层数、片层尺寸、分散性等纳米结构。表征结果显示水热法可以成功地将MoS₂高分散、均匀地负载在rGO表面,且可以通过调控钼源种类调变MoS₂/rGO催化剂中MoS₂催化加氢活性位。采用蒽作为重质油模型化合物评价了MoS₂/rGO催化剂的催化加氢性能,结果表明以四硫代钼酸铵为钼源水热法制备的MoS₂/rGO-ATTM催化剂蒽加氢率和八氢蒽选择性分别是浸渍法制备IM-MoS₂/rGO催化剂的2.0倍和4.2倍。MoS₂/rGO催化剂的催化加氢活性与比表面积无关,主要取决于其上MoS₂纳米片的堆积层数和片层长度。MoS₂/rGO-ATTM催化剂的高催化加氢活性可以归结于其上MoS₂纳米片的高催化加氢活性位暴露量、催化剂的高分散性和高悬浮性。     

Magnetically separable Pt catalyst for asymmetric hydrogenation

A magnetic Pt/SiO₂/Fe₃O₄ catalyst consisting of chirally modified platinum supported on silica coated magnetite nanoparticles was prepared using an easy synthetic route and successfully applied for the enantioselective hydrogenation of various activated ketones. The magnetic catalyst modified with cinchonidine showed a catalytic performance (activity, enantioselectivity) in the asymmetric hydrogenation of various activated ketones in toluene comparable to the best known Pt/alumina catalyst used for these reactions. The novel catalyst can be easily separated from the reaction solution by applying an external magnetic field and recycled several times with almost complete retention of activity and enantioselectivity.     

Preparation of supported skeletal Ni catalyst and its catalytic performance on dicyclopentadiene hydrogenation

Preparation and catalytic performance of skeletal Ni catalysts supported on Al₂O₃ were studied. The effects of alloy powder/pseudo-boehmite powder mass ratios and calcination temperatures of precursors on surface properties, compressive strength and catalytic performance were investigated. It was found that catalysts prepared by precursors which were molded with alloy powder/pseudo-boehmite powder mass ratio of 4/6 and calcinated at 860 °C in air atmosphere exhibited excellent compressive strength (16.11 N/mm), high dicyclopentadiene conversion (> 95%) and appropriate THDCPD selectivity (> 50%) during 1000-hour evaluation. The operational conditions were obtained as following: T = 120 °C, P = 2.0 MPa, LSHV = 2.0 h^− 1 and hydrogen–oil ratio = 300:1.     

Efficient new supported catalyst for asymmetric reductions

Heterogeneous catalysis is important for fine chemistry, especially for the synthesis of optically active molecules. Here, we present a new supported catalyst: the oxazaborolidine immobilised on silica. These molecules are well known in homogeneous conditions and provide excellent activity and selectivity for the reduction of ketones. The problems of the separation of the catalyst and product and the difficult recovery of the catalyst lead us to heterogenize this system.     

Reduced graphene oxide and ZnO decorated graphene for biomedical applications

The ability of graphene-based materials to enhance the conventional antibiotic resistance is well known and researchers have been interested in improving their antibacterial activity. The reduction of graphene oxide by eco-friendly reducing agents is of great interest on the basis of environmental and human health aspects. Herein we report the synthesis of two forms of graphene derivatives namely, reduced graphene oxide (RGO) through reduction using potato starch and zinc oxide decorated RGO (ZnO-RGO). In the case of ZnO-RGO, the reduction of graphene oxide and the conversion of ZnO to nano ZnO occur simultaneously. The characterization of all the graphene based materials and nanocomposites developed were carried out using FT-IR, XRD, Raman spectra and TEM techniques. The antibacterial activity of these modified materials against E. coli was also studied by well diffusion method. Our results show that ZnO-RGO is more efficient than RGO in their antibacterial properties which we attribute to the synergistic effect of ZnO and RGO towards the bacteria in the nanocomposite. Further we find that the antibacterial effect of ZnO-RGO towards E. coli is due to the disruption of the bacterial cell which could be confirmed by AFM images. Considering the fact that graphene-based materials are less toxic towards mammalian cells, both RGO and ZnO-RGO we have developed can find applications in the field of medicine and life sciences.     

手性膦配体在不对称催化氢化中的研究进展

综述了手性膦配体与Rh或Ru的配合物在活性羰基化合物手性催化氢化应用中的研究进展。     

一种具有温敏表面的氧化石墨烯负载钯催化剂的制备及催化性能

以过硫酸铵（APS）为引发剂,N-异丙基丙烯酰胺（NIPAM）为单体,在氧化石墨烯（GO）表面生长温敏高分子聚（N-异丙基丙烯酰胺）（PNIPAM）,获得复合载体GO-PNIPAM,并通过水相浸渍还原法制备具有温度敏感特性的Pd催化剂（Pd/GO-PNIPAM）。采用红外光谱、差示量热、热重、元素分析、透射电镜和电感耦合等离子原子发射光谱对复合载体GO-PNIPAM和Pd催化剂进行表征。结果表明,PNIPAM在GO上的接枝率约占60%。GO-PNIPAM显示出明显的温敏效应,其最低临界溶液温度约37℃。Pd/GO-PNIPAM上Pd纳米颗粒的平均粒径为(4.70±0.85)nm,远小于Pd/GO中Pd平均粒径(8.79±2.68)nm。因此,PNIPAM在GO上的接枝为金属纳米颗粒的沉积提供了大量的锚定位点,有助于金属纳米颗粒在其上的分散。Pd/GO-PNIPAM在高温下（80℃）肉桂醛（CAL）的选择性加氢反应中显示出优良的催化性能,初始转换频率（initial TOF）达192.3min^-1,高于GO负载Pd催化剂（Pd/GO,103.5min^-1）。Pd/GO-PNIPAM较高的Pd纳米颗粒分散性和高温下对CAL良好的吸附性能协同作用,导致其催化活性提高。     

Selective hydrogenation of nitroarenes using gum acacia supported Pt colloid an effective reusable catalyst in aqueous medium

An efficient green synthesis of Pt nanoparticles in water has been developed using gum acacia, both as reducing and stabilizing agent. The colloidal platinum efficiently catalyzes hydrogenation of nitroarenes to arylamines employing molecular hydrogen as the reductant. Excellent yields of products were obtained with a wide range of substrates and the catalyst was reused for several cycles with consistent activity.     

Reduced graphene oxide supported highly porous V2O5 spheres as a high-power cathode material for lithium ion batteries

Reduced graphene oxide (rGO) supported highly porous polycrystalline V(2)O(5) spheres (V(2)O(5)/rGO) were prepared by using a solvothermal approach followed by an annealing process. Initially, reduced vanadium oxide (rVO) nanoparticles with sizes in the range of 10-50 nm were formed through heterogeneous nucleation on rGO sheets during the solvothermal process. These rVO nanoparticles were oxidized to V(2)O(5) after the annealing process in air at 350 °C and assembled into polycrystalline porous spheres with sizes of 200-800 nm. The weight ratio between the rGO and V(2)O(5) is tunable by changing the weight ratio of the precursors, which in turn affects the morphology of V(2)O(5)/rGO composites. The V(2)O(5)/rGO composites display superior cathode performances with highly reversible specific capacities, good cycling stabilities and excellent rate capabilities (e.g. 102 mA h g(-1) at 19 C).     

Rhodium complexes containing chiral P-donor ligands as catalysts for asymmetric hydrogenation in non conventional media

Abstract  

Rhodium-catalysed asymmetric hydrogenation using P-donor ligands, such as new fluorinated (R)-BINOL and azadioxaphosphabicyclo[3.3.0]octane derivatives was carried out in different reaction media such as organic solvent (CH₂Cl₂), ionic liquid ([BMI][PF₆]), supercritical carbon dioxide (scCO₂) and [BMI][PF₆]/scCO₂ mixture. The best enantioselectivities were obtained in neat [BMI][PF₆], allowing a recycling up to ten times without activity loss. However, the enantioselectivity was lost due to ligand leaching. The ionic liquid phase containing rhodium molecular species was supported on functionalized multi-walled carbon nanotubes in order to improve the recycling, but unfortunately the asymmetric induction was lost upon catalyst immobilization.     

Benzene selective hydrogenation over supported Ni (nano-) particles catalysts: Catalytic and kinetics studies

This report aims to reduce the benzene in a mixture of benzene and toluene as a model reaction using catalytic hydrogenation. In this research, we developed a series of catalysts with different supports such as Ni/HMS, Ni/HZSM-5, Ni/HZSM5-HMS, Ni/Al_2O_3 and Ni/SiO_2. Kinetic of this reaction was investigated under various hydrogen and benzene pressures. For more study, two kinetic models have also been selected and tested to describe the kinetics for this reaction. Both used models, the power law and Langmuir–Hinshelwood, provided a good fit toward the experimental data and allowed to determine the kinetic parameters. Among these catalysts, Ni/Al_2O_3 showed the maximum benzene conversion(99.19%) at 130 °C for benzene hydrogenation. The lowest toluene conversion was observed for Ni/SiO_2. Furthermore, this catalyst presented high selectivity to benzene(75.26%)at 130 °C. The catalytic performance(activity, selectivity and stability) and kinetics evaluations were shown that the Ni/SiO_2 is an effective catalyst to hydrogenate benzene. It seems that the surface properties particularly pore size are effective parameter compared to other factors such as acidity and metal dispersion in this process.     

负载型Ni-Pt-B非晶态合金催化剂的制备及其苯加氢性能

以拟薄水铝石、丝光沸石为原料制备载体,采用浸渍-化学还原法制备了负载型Ni-Pt-B非晶态合金催化剂,并对催化剂进行XRD、BET和H2-TPR表征。以苯加氢制环己烷反应为探针,考察Pt、还原物溶剂碱浓度、浸渍顺序等因素对催化剂加氢活性的影响。结果表明,以H2PtCl6·6H2O为原料添加的微量Pt能促进NiO的还原,并显著提高催化剂苯加氢活性;还原物溶剂为蒸馏水,采用Ni、Pt共浸渍并干燥后还原的方法制备的催化剂活性最好。在反应压力0.5MPa、氢苯摩尔比4∶1,质量空速1.0h-1的条件下,反应温度高于120℃时,环己烷产率达到100%。     

Reduced chemically modified graphene oxide for supercapacitor electrode

An efficient active material for supercapacitor electrodes is prepared by reacting potassium hydroxide (KOH) with graphene oxide followed by chemical reduction with hydrazine. The electrochemical performance of KOH treated graphene oxide reduced for 24 h (reduced chemically modified graphene oxide, RCMGO-24) exhibits a specific capacitance of 253 F g^-1 at 0.2 A g^-1 in 2 M H₂SO₄ compared to a value of 141 F g^-1 for graphene oxide reduced for 24 h (RGO-24), and good cyclic stability up to 3,000 cycles. Interestingly, RCMGO-24 demonstrated a higher specific capacitance and excellent cycle stability due to its residual oxygen functional groups that accelerate the faradaic reactions and aid in faster wetting. This non-annealed strategy offers the potential for simple and cost-effective preparation of an active material for a supercapacitor electrode.     

Thiol-functionalized magnetite/graphene oxide hybrid as a reusable adsorbent for Hg2+ removal

A thiol-functionalized magnetite/graphene oxide (MGO) hybrid as an adsorbent of Hg²⁺ was successfully synthesized by a two-step reaction. It exhibited a higher adsorption capacity compared to the bare graphene oxide and MGO due to the combined adsorption of thiol groups and magnetite nanocrystals. Its capacity reached 289.9 mg g^-1 in a solution with an initial Hg²⁺ concentration of 100 mg l^-1. After being exchanged with H⁺, the adsorbent could be reused. The adsorption of Hg²⁺ by the thiol-functionalized MGO fits well with the Freundlich isotherm model and followed pseudo-second-order kinetics.     

负载型纳米金催化剂在乙炔选择性加氢反应中的研究进展

介绍了乙炔选择性加氢制乙烯催化剂的研究和开发进展。针对负载型纳米金催化剂的发展趋势及其对乙炔加氢反应产物中乙烯的独特选择性,重点对比单金属纳米金催化剂及合金型催化剂的催化性能差异,发现合金型纳米金催化剂具有较高的乙炔转化率和稳定性。影响催化性能的主要因素有纳米粒子的大小及活性组分之间的相互协同作用。分析积炭的形成以及导致催化剂失活的原理。展望低温条件下具有高转化率与高稳定性的合金型纳米金催化剂的应用前景。