Synthesis of discrete and dispersible MoS2 nanocrystals

MoS2 nanoparticles of size <5 nm have been synthesized via the reaction of Mo(CO)6 with elemental sulfur in trioctylphosphine oxide and 1-octadecene at temperatures from 270 to 330 degrees C. The MoS2 nanoparticles are discrete and dispersible in a variety of nonpolar organic solvents, including toluene, chloroform, and pyridine. The size of the particles can be effectively tuned by varying the temperature, yielding nearly monodisperse samples (<10% standard deviation) as evidenced by transmission electron microscopy (TEM). Additionally, larger (20-50 nm) onion- and tube-shaped MoS2 nanoparticles can be obtained by decreasing the amount of the coordinating solvent (trioctylphosphine oxide) relative to 1-octadecene. As-prepared samples are poorly crystalline, showing only weak contrast in the TEM and an absence of the first-order (00 l) reflection in powder X-ray diffraction that is indicative of regular MoS2 stacking. Samples heated in situ in the TEM are observed to develop contrast and lattice fringes as the temperature is raised to 550 degrees C. Ex-situ heated samples show the appearance of the first order (00l) reflection at temperatures >870 degrees C.     

碳包覆Pd/TiO2光催化产氢协同胺类选择性氧化合成亚胺(英文)

负载型金属纳米催化剂由于其优异的光催化性能,被广泛应用于光催化产氢协同胺类氧化偶联合成高附加值亚胺体系。但在反应过程中,金属表面对H原子和亚胺表现出较强的吸附能力,导致了亚胺易于发生自氢化反应而生成仲胺,显著降低了亚胺的选择性。在本文中,我们证实了在Pd/Ti O₂表面构建超薄碳层(Pd/Ti O₂@C)是一种解决上述问题的有效策略。在Pd/Ti O₂表面构筑的超薄碳层可以有效调控H原子和亚胺在其表面的吸附行为,避免了光催化氧化偶联过程中亚胺的自氢化。因此,Pd/Ti O₂@C光催化剂在光催化产氢协同胺类选择性氧化合成亚胺体系中展现出优异的亚胺选择性。本研究提供了一种便捷有效的策略推动负载型金属纳米催化剂在光催化产氢协同合成高附加值产物体系中的应用。     

金属有机骨架高温自还原制备高性能等级孔碳负载Co基催化剂

以钴基金属有机框架为前驱体, 利用一步高温碳化自还原法, 通过精确调控碳化过程, 实现等级孔道结构及钴纳米颗粒分散性的可控调节, 制备出高催化活性及产物选择性的等级孔碳负载Co基催化剂. 研究发现, 600 ℃碳化后的催化剂为具有高比表面积的等级孔道结构和高分散的钴纳米颗粒, 在选择性催化1,3-丁二烯加氢反应中, 丁二烯完全转化温度低至60 ℃, 对应丁烯的选择性高达61%, 实现了低温高选择性催化加氢.     

Fullerene-like (IF) Nb(x)Mo(1-x)S2 nanoparticles

IF-Mo1-xNbxS2 nanoparticles have been synthesized by a vapor-phase reaction involving the respective metal halides with H2S. The IF-Mo1-xNbxS2 nanoparticles, containing up to 25% Nb, were characterized by a variety of experimental techniques. Analysis of the powder X-ray powder diffraction, X-ray photoelectron spectroscopy, and different electron microscopy techniques shows that the majority of the Nb atoms are organized as nanosheets of NbS2 within the MoS2 host lattice. Most of the remaining Nb atoms (3%) are interspersed individually and randomly in the MoS2 host lattice. Very few Nb atoms, if any, are intercalated between the MoS2 layers. A sub-nanometer film of niobium oxide seems to encoat the majority of the nanoparticles. X-ray photoelectron spectroscopy in the chemically resolved electrical measurement mode (CREM) and scanning probe microscopy measurements of individual nanoparticles show that the mixed IF nanoparticles are metallic independent of the substitution pattern of the Nb atoms in the lattice of MoS2 (whereas unsubstituted IF-MoS2 nanoparticles are semiconducting). Furthermore the IF-Mo1-xNbxS2 nanoparticles are found to exhibit interesting single electron tunneling effects at low temperatures.     

Cluster-support interactions and morphology of MoS2 nanoclusters in a graphite-supported hydrotreating model catalyst

Supported MoS(2) nanoparticles constitute the active component of the important hydrotreating catalysts used for industrial upgrading and purification of the oil feedstock for the production of fossil fuels with a low environmental load. We have synthesized and studied a model system of the hydrotreating catalyst consisting of MoS(2) nanoclusters supported on a graphite surface in order to resolve a number of very fundamental questions related to the atomic-scale structure and morphology of the active clusters and in particular the effect of a substrate used in some types of hydrotreating catalysts. Scanning tunneling microscopy (STM) is used to image the atomic-scale structure of graphite-supported MoS(2) nanoclusters in real space. It is found that the pristine graphite (0001) surface does not support a high dispersion of MoS(2), but by introducing a small density of defects in the surface, highly dispersed MoS(2) nanoclusters could be synthesized on the graphite. From high-resolution STM images it is found that MoS(2) nanoclusters synthesized at low temperature in a sulfiding atmosphere preferentially grow as single-layer clusters, whereas clusters synthesized at 1200 K grow as multilayer slabs oriented with the MoS(2)(0001) basal plane parallel to the graphite surface. The morphology of both single-layer and multilayer MoS(2) nanoclusters is found to be preferentially hexagonal, and atom-resolved images of the top facet of the clusters provide new atomic-scale information on the MoS(2)-HOPG bonding. The structure of the two types of catalytically interesting edges terminating the hexagonal MoS(2) nanoclusters is also resolved in atomic detail in STM images, and from these images it is possible to reveal the atomic structure of both edges and the location and coverage of sulfur and hydrogen adsorbates.     

量子电动学诱导电磁辐射研究纳米催化剂

Gold has been regarded as a poor heterogeneous catalyst because it is generally considered a nonreactive metal. But as nanocatalysts,gold and other metals somehow significantly enhance reactivity. It is generally thought chemical bonds of reactants are weakened by adsorption to nanocatalysts thereby allowing reactions to proceed more rapidly,but how this reaction proceeds to completion is not well understood. Here gold nanocatalysts are treated as unsupported nanoparticles (NPs) in a solution of reactant molecules from which extensions are made to gold NPs supported on titanium dioxide. Whether the NPs are supported or unsupported,enhanced catalytic reactivity depends on absorbed thermal kT (k is Boltzmann's constant and T is absolute temperature) energy accumulated from prior collisions of reactant molecules. The accumulated kT energy is treated as electromagnetic thereby allowing frequency up-conversion by quantum electrodynamics (QED) to the confinement frequency of the NP,typically beyond the vacuum ultraviolet (VUV). By this theory,the chemical reaction of reactant molecules having bonds weakened by adsorption is completed by QED induced VUV photolysis.     

MoS2 nanoparticles grown on graphene: an advanced catalyst for the hydrogen evolution reaction

Advanced materials for electrocatalytic and photoelectrochemical water splitting are central to the area of renewable energy. In this work, we developed a selective solvothermal synthesis of MoS(2) nanoparticles on reduced graphene oxide (RGO) sheets suspended in solution. The resulting MoS(2)/RGO hybrid material possessed nanoscopic few-layer MoS(2) structures with an abundance of exposed edges stacked onto graphene, in strong contrast to large aggregated MoS(2) particles grown freely in solution without GO. The MoS(2)/RGO hybrid exhibited superior electrocatalytic activity in the hydrogen evolution reaction (HER) relative to other MoS(2) catalysts. A Tafel slope of ～41 mV/decade was measured for MoS(2) catalysts in the HER for the first time; this exceeds by far the activity of previous MoS(2) catalysts and results from the abundance of catalytic edge sites on the MoS(2) nanoparticles and the excellent electrical coupling to the underlying graphene network. The ～41 mV/decade Tafel slope suggested the Volmer-Heyrovsky mechanism for the MoS(2)-catalyzed HER, with electrochemical desorption of hydrogen as the rate-limiting step.     

Pt/oxide nanocatalysts synthesized via the ultrasonic spray pyrolysis process: engineering metal–oxide interfaces for enhanced catalytic activity

We show that Pt nanoparticles synthesized on oxide nanocatalysts exhibit catalytic activity enhancement depending on the type of the oxide support. To synthesize the Pt/oxide nanocatalysts, we employed a versatile synthesis method using Pt nanoparticles (NPs) supported on various metal oxides (i.e., SiO₂, CeO₂, Al₂O₃, and FeAl₂O₄) utilizing ultrasonic spray pyrolysis. Catalytic CO oxidation was carried out on these catalysts, and it was found that the catalytic activity of the Pt NPs varied depending on the supporting oxide. While Pt/CeO₂ exhibited the highest metal dispersion and active surface area, Pt/FeAl₂O₄ exhibited the lowest active surface area. Among the Pt/oxide nanocatalysts, Pt NPs supported on CeO₂ showed the highest catalytic activity. We ascribe the enhancement in turnover frequency of the Pt/CeO₂ nanocatalysts to strong metal–support interactions due to charge transport between the metal catalysts and the oxide support. Such Pt/oxide nanocatalysts synthesized via spray pyrolysis offer potential possibilities for large-scale synthesis of tailored catalytic systems for technologically relevant applications.     

聚苯胺/贵金属复合纳米材料的可控合成及催化应用

导电高分子/贵金属复合纳米材料因其在催化、传感、表面增强拉曼、光热治疗等诸多领域的应用前景而受到广泛关注.本文主要介绍我们课题组近年来利用可控合成策略制备的负载型和包埋型两种结构聚苯胺/贵金属复合纳米材料,以及利用复合纳米材料的结构和功能特性,对其在多相催化领域的应用、结构与催化性能之间构效关系的探索.     

Composite surfactants aided solvothermal synthesis and catalytic hydrogenation property of oil soluble bimetallic CoMoS nanoparticles

Oil-soluble bimetallic CoMoS nanoparticles were successfully synthesized by a composite-surfactants-aided-solvothermal process. The surface hydrophilicity and functionality of the products were investigated through transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectra, and Ultraviolet (UV) spectra analysis. The catalytic performance of hydrogenation on the CoMoS nanoparticles was studied with naphthalene as a model compound. It was found that CoMoS catalysts supported on active carbon (AC) was more active than conventional MoS2/γ-Al2O3. The activity of CoMoS/AC can be tailored through the change of the Co/(Co+Mo) atomic ratio.     

燃料电池纳米催化剂的稳定化

低温燃料电池是理想的移动式电源,它所采用的电催化剂主要为Pt基贵金属纳米催化剂。提高纳米催化剂在电池内部环境中的稳定性、抑制其活性衰减,对于延长低温燃料电池的使用寿命和节约成本具有十分重要的意义。本文从三个方面综述了近年来在低温燃料电池纳米催化剂稳定化方面的研究进展。首先,通过载体效应实现催化剂的稳定化,包括碳载体的石墨化、碳载体的掺杂、表面功能化及其他载体的采用等。其次,通过空间效应实现催化剂的稳定化,包括催化剂粒子表面覆盖、催化剂粒子微孔嵌入、催化剂表面杂多酸单层自组装及聚合物电解质空间阻隔等。再其次,通过协同效应实现催化剂的稳定化,包括提升金属粒子的氧化电位、强化组分间的相互作用等。最后,对低温燃料电池纳米催化剂稳定化的发展前景进行了展望。     

复合半导体MoS_2/Cu_2O的制备及其光催化性能研究

采用两步法制备了MoS_2/Cu_2O催化剂,对其催化降解甲基橙(MO)性能进行了研究.首先,通过液相剥离和梯度离心获得少数层MoS_2纳米片,然后采用水热还原法在MoS_2纳米片上合成Cu_2O纳米颗粒,形成MoS_2/Cu_2O复合半导体,并分别通过扫描电子显微镜(SEM)、X射线衍射(XRD)、X射线光电子能谱(XPS)、UV-Vis紫外可见漫反射光谱(DRS)等手段对催化剂的结构进行表征.在可见光下,MoS_2/Cu_2O复合半导体降解MO的效率明显高于纯MoS_2和Cu_2O.为了获得最佳光催化活性,探究了MoS_2质量分数(5%、10%、20%、30%、40%、50%)对MoS_2/Cu_2O复合半导体光催化降解MO的影响.最后,经过5次循环实验,MoS_2/Cu_2O降解率下降为82.5%,循环稳定性有待进一步提高.     

Preparation and electrocatalytic properties of Pt-SiO2 nanocatalysts for ethanol electrooxidation

Due to their high stability in general acidic solutions, SiO(2) nanoparticles were selected as the second catalyst for ethanol oxidation in sulfuric acid aqueous solution. Pt-SiO(2) nanocatalysts were prepared in this paper. The micrography and elemental composition of Pt-SiO(2) nanoparticles were characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy, respectively. The electrocatalytic properties of Pt-SiO(2) nanocatalysts for ethanol oxidation were investigated by cyclic voltammetry. Under the same Pt loading mass and experimental conditions for ethanol oxidation, Pt-SiO(2) nanocatalysts show higher activity than PtRu/C (E-Tek), Pt/C (E-Tek), and Pt catalysts. Additionally, Pt-SiO(2) nanocatalysts possess good anti-poisoning ability. The results indicate that Pt-SiO(2) nanocatalysts may have good potential applications in direct ethanol fuel cells.     

Synthesis of green nanocatalysts and industrially important green reactions

Abstract

There is a growing interest in applying green chemistry for nanocatalysis applications. On the basis of a Scifinder Scholar search, the field of applying green chemistry to catalysis with nanoparticles has undergone an explosive growth from year 2002 to present. It can be seen that green chemistry applied to nanocatalysis is a relatively hot area with much room for growth. I discuss several review articles written about the use of green nanocatalysts as well as green reactions. I discuss studies involving the synthesis of green nanocatalysts and application of metal nanocatalysts in green reactions. I have organized the discussion of green nanocatalysts by the type of nanoparticles that are synthesized and used as catalysts. I have organized discussions of green reactions by the type of green reaction that is being conducted. Overall, our review article discusses developments in new types of green nanocatalysts as well as developments in green catalytic reactions.     

Model catalysts of supported Au nanoparticles and mass-selected clusters

In surface science, much effort has gone into obtaining a deeper understanding of the size-selectivity of nanocatalysts. In this article, electronic and chemical properties of various model catalysts consisting of Au are reported. Au supported by oxide surfaces becomes inert towards chemisorption and oxidation as the particle size became smaller than a critical size (2-3 nm). The inertness of these small Au nanoparticles is due to the electron-deficient nature of smaller Au nanoparticles, which is a result of metal-substrate charge transfer. Properties of Au clusters smaller than ～20 atoms were shown to be non-scalable, i.e., every atom can drastically change the chemical properties of the clusters. Moreover, clusters with the same size can show dissimilar properties on various substrates. These recent endeavours show that the activity of a catalyst can be tuned by varying the substrate or by varying the cluster size on an atom-by-atom basis.     

聚苯并噁嗪固载钯基纳米催化剂在芳香醇氧化反应中的应用

以球状聚苯并噁嗪为载体, 采用浸渍热解法合成了钯炭纳米催化剂. 通过透射电子显微镜观察发现, 钯纳米粒子几乎全部均匀分布在载体上, 且尺寸均一, 平均直径约为3.5 nm. 结果表明, 载体表面含有丰富的含氮含氧官能团, 氮和氧原子与钯之间存在相互作用, 从而使聚苯并噁嗪能够有效固载钯纳米粒子. 采用相同的方法进一步合成Pd-Au/C和Pd-Pt/C双金属催化剂, Pd-Au和Pd-Pt纳米粒子也展现出良好的分散性, 无明显团聚现象, 平均直径分别为4.3和4.2 nm, 进一步说明聚苯并噁嗪对金属活性组分的有效固载. 将催化剂应用于苯甲醇氧化反应, 其中Pd₁-Au₁/C在2 h的转化率为98%, 对产物苯甲醛的选择性大于99%, 该催化剂经过焙烧可恢复催化活性, 表现出良好的循环稳定性, 并能将不同取代基的芳香醇氧化为相应的醛, 是一种良好的醇氧化催化剂.     

Based on MFe2O4 (M=Co,Cu, and Ni): Magnetically recoverable nanocatalysts in synthesis of heterocyclic structural scaffolds

Abstract

Catalysis research under magnetically recoverable nanocatalysts is a well-known topic in organic synthesis. In recent times, catalysis research has clearly experienced a renaissance in the area of utility of ferrite nanoparticles based on their ability to recovery and reusability. In this review, the focus is on the fabrication, characterization and of application the MFe₂O₄ (M=Co, Cu, and Ni) nanocatalysts in synthesis of heterocyclic structural scaffolds.     

Ultrastable Au nanocatalyst supported on surface-modified TiO2 nanocrystals

The surfaces of TiO2 nanocrystals were modified with amorphous aluminum-oxide layers using a surface sol-gel process to control the interaction between supports and metal particles. Ultrastable Au nanocatalysts were prepared by the deposition of Au nanoparticles on the surface-modified TiO2 nanocrystals using a deposition-precipitation (DP) method. The TEM analysis showed that the Au nanoparticles on the surface-modified nanocrystal supports were highly stable with a sinter-resistant capability during high-temperature calcination. The HRTEM analysis revealed that the surface of the TiO2 nanocrystals was covered by an amorphous aluminum-oxide layer and the Au nanoparticles were primarily anchored to this amorphous layer. This amorphous aluminum-oxide layer played an extremely important role in the stabilization of the supported Au nanoparticles without affecting catalytic activities. The surface modification of nanocrystal supports highlights new opportunities in tailoring the stability and activity of supported nanocatalyst systems.     

Copper Based Nanoparticles-Catalyzed Organic Transformations

Copper (Cu) based nanoparticles mediated organic transformations have been focused worldwide because these methodologies afford industrially important fine chemicals under mild conditions. Moreover, Cu is environment friendly and relatively inexpensive. This review highlights the important developments of Cu based nanocatalysts for organic transformations.