Yongjun Ji

Yolk Bishell MnxCo1-xFe2O4 Hollow Microspheres and Their Embedded Form in Carbon for Highly Reversible Lithium Storage

The yolk-shell hollow structure of transition metal oxides has many applications in lithium-ion batteries and catalysis. However, it is still a big challenge to fabricate uniform hollow microspheres with the yolk bishell structure for mixed transition metal oxides and their supported or embedded forms in carbon microspheres with superior lithium storage properties. Here we report a new approach to the synthesis of manganese cobalt iron oxides/carbon (MnxCo1-xFe2O4 (0 ≤ x ≤ 1)) microspheres through carbonization of Mn(2+)Co(2+)Fe(3+)/carbonaceous microspheres in N2, which can be directly applied as high-performance anodes with a long cycle life for lithium storage. Furthermore, uniform hollow microspheres with a MnxCo1-xFe2O4 yolk bishell structure are obtained by annealing the above MnxCo1-xFe2O4/carbon microspheres in air. As demonstrated, these anodes exhibited a high reversible capacity of 498.3 mAh g(-1) even after 500 cycles for Mn0.5Co0.5Fe2O4/carbon microspheres and 774.6 mAh g(-1) over 100 cycles for Mn0.5Co0.5Fe2O4 yolk bishell hollow microspheres at the current density of 200 mA g(-1). The present strategy not only develops a high-performance anode material with long cycle life for lithium-ion batteries but also demonstrates a novel and feasible technique for designed synthesis of transition metal oxides yolk bishell hollow microspheres with various applications.

Synergistic effect in bimetallic copper–silver (CuxAg) nanoparticles enhances silicon conversion in Rochow reaction

The oleylamine thermal reduction process was employed to prepare bimetallic copper–silver (CuxAg (0 ≤ x ≤ 50)) nanoparticles, such as Cu, Cu50Ag, Cu20Ag, Cu10Ag, Cu5Ag, CuAg, CuAg2, and Ag, by using Cu(CH3COO)2 and AgNO3 as the precursors. The samples were characterized by X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy. The CuxAg hybrid nanostructure showed good particle dispersion, and Cu and Ag metals were well mixed. The catalytic properties of these bimetallic CuxAg nanoparticles as model catalysts for the Rochow reaction were explored. Compared to monometallic Cu and Ag nanoparticles, bimetallic CuxAg nanoparticles resulted in a much higher silicon conversion, which is attributed to the synergistic electronic effect between Cu and Ag metals. For example, the Cu atom was observed to have a lower electron density in the CuxAg bimetallic nanoparticle than that in monometallic Cu nanoparticles, which enhanced the formation of methylchlorosilanes on the silicon surface with chloromethane, demonstrating the significance of the CuxAg bimetallic catalysts in catalytic reactions during organosilane synthesis. The insights gained in this study should be conducive to the design of good Cu-based catalysts for the Rochow reaction.

One-dimensional Cu-based catalysts with layered Cu–Cu2O–CuO walls for the Rochow reaction

A series of copper catalysts with a core–shell or tubular structure containing various contents of Cu, Cu2O, and CuO were prepared via controlled oxidation of Cu nanowires (NWs) and used in the synthesis of dimethyldichlorosilane (M2) via the Rochow reaction. The Cu NWs were prepared from copper (II) nitrate using a solution-based reduction method. The samples were characterized by X-ray diffraction, thermogravimetric analysis, temperature-programmed reduction, X-ray photoelectron spectroscopy, transmission electron microscopy, and scanning electron microscopy. It was found that the morphology and composition of the catalysts could be tailored by varying the oxidation temperature and time. During the gradual oxidation of Cu NWs, the oxidation reaction initiated on the outer surface and gradually developed into the bulk of the NWs, leading to the formation of catalysts with various structures and layered compositions, e.g., Cu NWs with surface Cu2O, ternary Cu–Cu2O–CuO core–shell NWs, binary Cu2O–CuO nanotubes (NTs), and single CuO NTs. Among these catalysts, ternary Cu–Cu2O–CuO core–shell NWs exhibited superior M2 selectivity and Si conversion in the Rochow reaction. The enhanced catalytic performance was mainly attributed to improved mass and heat transfer resulting from the peculiar heterostructure and the synergistic effect among layered components. Our work indicated that the catalytic property of Cu-based nanoparticles can be improved by carefully controlling their structures and compositions.

Heterojunctions generated in SnO2-CuO nanocatalysts for improved catalytic property in the Rochow reaction

We report the improved catalytic performance of SnO2-CuO hybrid nanocatalysts synthesized by rationally designing and controlling the local heterojunction structure. The SnO2 nanoparticle (NP) decorated CuO nanorods (NRs) (SnO2-CuO) with a mace-like structure and with various CuO : SnO2 ratios were prepared via depositing pre-synthesized SnO2 NPs on CuO NRs in the presence of polyvinylpyrrolidone molecules. The CuO NRs were obtained by a facile hydrothermal reaction using Cu(NO3)(2)center dot 3H(2)O as the precursor. The samples were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and temperature-programmed reduction analyses. The results indicated that in the SnO2-CuO hybrid nanostructures, the heterojunctions were well generated as the SnO2 NPs were well dispersed on the CuO NRs. Their catalytic performances were then explored via the Rochow reaction, in which solid silicon (Si) reacts with gaseous methyl chloride (MeCl) to produce dimethyldichlorosilane (M2). Compared to separate CuO and SnO2 as well as their physical mixture, the SnO2-CuO hybrids exhibit significantly enhanced M2 selectivity and Si conversion because of the enhanced synergistic interaction between SnO2 and CuO due to the generated heterojunctions. This work demonstrates that the performance of heterogeneous catalysts can be improved by carefully designing and controlling their structures even when their composition remains unchanged.

Rambutan-like hierarchically heterostructured CeO2-CuO hollow microspheres: Facile hydrothermal synthesis and applications

Hierarchically heterostructured hollow spheres are of great interest for a wide range of applications owing to their unique structural features and properties. However, the fabrication of well-defined hollow spheres with highly specific morphology for mixed transition metal oxides on a large scale remains challenging. In this work, uniform rambutan-like heterostructured CeO2-CuO hollow microspheres with numerous copper–ceria interfacial sites and nanorods and nanoparticles as building blocks are prepared via a facile hydrothermal method followed by calcination. Importantly, this approach can be readily scaled up and is applicable to the synthesis of various CuO-based mixed metal oxide complex hollow spheres. The as-prepared CeO2-CuO hollow rambutans exhibit superior performance both as electrode materials for supercapacitors and as Cu-based catalysts for the Rochow reaction, mainly due to the small primary nanoparticle constituents, high surface area, and formation of numerous interior heterostructures.

Morphology-dependent catalytic properties of nanocupric oxides in the Rochow reaction

Four kinds of CuO catalysts with well-controlled leaf-like (L-CuO), flower-like (F-CuO), sea-urchin-like (U-CuO), and oatmeal-like (O-CuO) morphologies were synthesized by a facile precipitation method assisted by various chelating ligands. High-resolution transmission electron microscopy and fast Fourier transform infrared spectroscopy indicated that the dominant crystal facets of L-CuO, F-CuO, U-CuO, and O-CuO were {001}, {1̅10}, {001}, and {110}, as well as {001} and {1̅10}, respectively. When tested for the Rochow reaction, it was found that their catalytic performances were dependent on their structures. Among the four CuO catalysts, L-CuO exhibited the best catalytic property, along with the strongest adsorption ability for oxygen and highest reducibility, which are mainly because of its largely exposed {001} facet and large specific surface area. In addition, the amount of the Cu3Si alloy phase, which is the most important reaction intermediate that generated in the reacted region of the Si surface, was measured for the different catalysts. Based on the findings, a detailed reaction mechanism was proposed. This work demonstrates that shape-controlled synthesis of oxide catalysts could be an effective strategy to design and develop efficient catalysts.

Porous (CuO)xZnO hollow spheres as efficient Rochow reaction catalysts

Nowadays, how to achieve both high dimethyldichlorosilane selectivity and silicon conversion in the Rochow reaction still remains a major challenge in the organosilane industry, in which silicon and chloromethane are converted into methylchlorosilanes on Cu-based catalysts mixed with ZnO promoter. Therefore, this calls for the development of outstanding catalysts with both high activity and selectivity for the Rochow reaction and also for a deep fundamental understanding of the catalytic mechanism. In this work, we designed and synthesized a series of copper oxide–zinc oxide catalysts ((CuO)xZnO (0 ≤ x ≤ 49)) with a distinct porous hollow spherical structure for the reaction. These porous hollow spherical catalysts composed of CuO and ZnO nanoparticles were prepared through co-adsorption of Cu2+ and Zn2+ in the interior and outer surfaces of the hydrothermally synthesized carbonaceous spheres, followed by a new hydrothermal treatment and calcination in air. The catalytic properties of the (CuO)xZnO hollow spheres for dimethyldichlorosilane synthesis via the Rochow reaction was investigated, and a deeper understanding of the catalytic mechanism was obtained. As compared to pure CuO hollow spheres, the prepared (CuO)19ZnO hollow spheres exhibited much higher dimethyldichlorosilane selectivity and silicon conversion, which are clearly related to the synergistic electronic effect between Cu and ZnO and to the distinct catalyst structures which allow intimate contact of the reactant molecules with the active component and the efficient transport of the molecules. This work opens a new way for the fabrication of efficient and integrated Cu-based catalysts for the Rochow reaction.

Honeycomb-like CuO/ZnO hybrid nanocatalysts prepared from solid waste generated in the organosilane industry

We report the preparation of honeycomb-like CuO/ZnO (CZx/y) nanocatalysts with CuO nanospheres (NSs) adhered with ZnO nanoparticles (NPs) for the Rochow reaction. The synthesis was carried out via adsorption of Cu2+/Zn2+ ions on carbon black (CB) which acted as both the agglomeration inhibitor and the hard template, and followed by calcination in air. The low cost Cu2+/Zn2+ ions were recovered from the solid waste generated in the organosilane industry via a simple ammonia leaching treatment. The samples were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and temperature-programmed reduction. The as-obtained CZx/y nanohybrids had a honeycomb-like structure with large voids and openings among the CuO NSs. When re-used as a Cu-based catalyst for the Rochow reaction, the CZx/y NPs sample with an optimized ratio showed significantly improved dimethyldichlorosilane (M2) selectivity and silicon (Si) conversion as compared with the CuO/ZnO NPs prepared in the absence of CB, discrete CuO or ZnO NPs and the CuO/ZnO NPs with different compositions, mainly due to the unique honeycomb-like structure, smaller crystal size and synergistic electronic effect at the interface between Cu and ZnO in CZx/y NPs.

Controllable wet synthesis of multicomponent copper-based catalysts for Rochow reaction

This work aims to provide a facile, low-cost and scalable method for the preparation of multicomponent Cu-Cu2O-CuO catalysts, which are of high interest to the organosilane industry. A series of submicrometer-sized and Cu-based catalysts containing CuO, Cu2O and Cu, or some combination of them, were synthesized by a simple low-temperature wet chemical method using CuSO4 center dot 5H(2)O as the precursor and N2H4 center dot H2O as a reducing agent. The samples were characterized by X-ray diffraction, thermogravimetric analysis, temperature-programmed reduction, X-ray photoelectron spectroscopy, transmission electron microscopy, and scanning electron microscopy techniques. It was observed that the composition of the samples could be tailored by varying the amount of reducing agent at a given reaction temperature and time. These catalysts were then tested in the Rochow reaction, using silicon powder and methyl chloride (MeCl) as reactants to produce dimethyldichlorosilane (M2), which is the most important organosilane monomer in the industry. Compared with bare CuO and Cu particles, the ternary CuO-Cu2O-Cu catalyst displayed much improved M2 selectivity and Si conversion, which can be attributed to the smaller copper particle size and the synergistic effect among the different components in the CuO-Cu2O-Cu catalyst. This catalyst preparation method is expected to yield efficient and low-cost copper catalysts for the organosilane industry.

Diffusion-controlled synthesis of Cu-based for the Rochow reaction

The properties of materials are strongly dependent on their structures. The diffusion effect is a main kinetic factor that can be used to regulate the growth and structure of materials. In this work, we developed a systematic and feasible strategy to synthesize Cu2O solid spheres and hexahedrons by controlling the diffusion coefficients. These Cu2O products can be successively transformed into corresponding Cu hollow spheres and hexahedrons as well as CuO porous spheres and hexahedrons by controlling hydrogen diffusion in hydrazine hydrate solution and controlling oxygen diffusion in air, respectively. The formation of these transformations was also discussed in detail. Tested for Rochow reaction, the as-prepared Cu2O solid and CuO porous spheres exhibit higher dimethyldichlorosilane selectivity and Si conversion than Cu hollow spheres, which is attributed to the active sites for CH3Cl adsorption formed in CuxSi phase after the removal of oxygen atoms in Cu2O and CuO in the formation of dimethylchlorosilane. The present work not only develops a feasible method for preparing well shape-defined Cu2O solid spheres and hexahedrons but also clarifies the respective roles of Cu, Cu2O and CuO in dimethyldichlorosilane synthesis via Rochow reaction.摘要大多数材料的功能和性质取决于它们的结构, 而扩散机制是调控材料生长和结构的一个主要动力学因素. 本工作提出了一条系统且可行的策略即通过控制扩散系数来制备Cu2O固体球和六面体, 且这些Cu2O产物可以分别通过水合肼溶液中氢原子扩散控制和空气中氧原子扩散控制, 转变成相应的Cu中空球和六面体, 以及CuO多孔球和六面体. 此外, 对转变过程的微观机制作了详尽的讨论; 用固定床评价了这些材料在用来合成有机硅行业广泛使用的单体的Rochow反应中的催化性能. 结果表明, 相较于Cu中空球, Cu2O固体球和CuO多孔球表现出了更高的二甲基二氯硅烷选择性和硅粉原料转化率, 这主要归因于在形成CuxSi活性相的过程中, Cu2O和CuO中的晶格氧去除以后形成的表面氧缺陷可以作为反应物CH3Cl的吸附活性位. 该工作不仅提出一种制备规整Cu2O固体球和六面体的可行方法, 而且揭示了Rochow反应合成单体二甲基二氯硅烷中Cu, Cu2O和CuO各自的催化作用.