Yongxia Zhu

Flower-like ZnO grown on urchin-like CuO microspheres for catalytic synthesis of dimethyldichlorosilane

We report the rational growth of flower-like ZnO on urchin-like CuO (f-ZnO@u-CuO) microspheres via a facile solvothermal method using copper nitrate and zinc nitrate as precursors in the presence of sodium nitrate and ethanol. A formation mechanism was proposed based on the observation of a series of reaction intermediates. The samples were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy with energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, inductively coupled plasma optical emission spectrometer, and temperature-programmed reduction. It was found that the morphology of the samples was highly dependent on the synthesis conditions, particularly the reaction time and the ammonia amount added. As a copper-based catalyst for dimethyldichlorosilane synthesis via the Rochow reaction, f-ZnO@u-CuO microspheres show better catalytic performance than the Cu-based catalysts physically mixed with ZnO promoter, probably because of the well-developed p-n heterojunction structures at the CuO and ZnO interfaces that generate a much strong synergistic effect. The work provides a simple method to synthesize hierarchical CuO/ZnO composites and would be helpful for understanding the catalytic mechanism of the Rochow reaction.

Controllably oxidized copper flakes as multicomponent copper-based catalysts for the Rochow reaction

The metallic Cu flakes prepared by milling metallic Cu powder were controllably oxidized in air at different temperatures to obtain the Cu-based catalysts containing multicomponents of Cu, Cu2O, and CuO. These catalysts are explored 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. The samples were characterized by X-ray diffraction, temperature-programmed reduction, thermogravimetric analysis, oxidimetry analysis, particle size analysis, transmission electron microscopy, and scanning electron microscopy. Compared to the metallic Cu powder and Cu flakes, the controllably oxidized Cu flakes containing Cu, Cu2O, and CuO species show much higher M2 selectivity and silicon conversion in the Rochow reaction. The enhanced catalytic performance may stem from the larger interfacial contact among the gas MeCl, solid Si particles, and solid Cu-based catalyst flakes, as well as the synergistic effect among the different Cu species. The work would be helpful to the development of novel Cu-based catalysts for organosilane synthesis.

Solvothermal synthesis of copper (I) chloride microcrystals with different morphologies as copper-based catalysts for dimethyldichlorosilane synthesis

CuCl microcrystals with different morphologies such as tetrahedra, etched tetrahedra, tripod dendrites, and tetrapods were synthesized using CuCl2⋅2H2O as the copper precursor in the mixed solvent of acetylacetone and ethylene glycol. The samples were characterized with X-ray diffraction, scanning electron microscopy, infrared spectroscopy, and transmission electron microscope. Cu(C5H7O2)2 was identified as the key intermediate, and the morphology and structure of the CuCl microcrystals were highly dependent on the reaction time and temperature, as well as the volume of the solvents. The catalytic properties of these CuCl microcrystals were explored in the dimethyldichlorosilane synthesis via Rochow reaction. Compared to the commercial CuCl microparticles with irregular morphology and dense internal structure, the obtained CuCl microcrystals possessed regular morphology and different exposed crystal planes and showed much higher dimethyldichlorosilane selectivity and Si conversion via the Rochow reaction because of the enhanced formation of active CuxSi phase and gas transportation within the dendritic structure, demonstrating the significance of regular morphology of the copper-based catalysts in catalytic organosilane synthesis.

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.

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.