Hezhi Liu

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.

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.