Lihua Jia

MnOx–CeO2 supported on a three-dimensional and networked SBA-15 monolith for NOx-assisted soot combustion

This paper reports the preparation and characterization of MnOx–CeO2/SBA-15 monolith (MnCe/SM) catalysts for NOx-assisted soot combustion. The SM with a three-dimensional (3D) network structure was synthesized by a sol–gel method, in which the shearing force and the acidity of the solution were finely tuned to direct the formation and assembly of the primary particles. The MnCe/SM catalysts were further prepared by a facile isovolumetric impregnation method. The samples were characterized by nitrogen adsorption, scanning electron microscopy, energy dispersed spectroscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, H2 temperature-programmed reduction, O2 temperature-programmed desorption, NO temperature-programmed desorption, and NO temperature-programmed oxidation. It is found that the MnOx–CeO2 nanoparticles were dispersed in the channels or/and on the outer surface of the SM support depending on the loading, and had a strong synergistic effect. The MnCe/SM catalysts with an appropriate MnOx–CeO2 loading showed much higher catalytic performance for soot combustion than that of the unsupported MnOx–CeO2 mixture. This is attributed to the combination of the MnOx–CeO2 active component with the 3D network structure of SM. The later not only provides large surface area and high accessibility for the soot particulates to the active sites, but also acts as a particulate filter.

Highly stable Ni/SiC catalyst modified by Al2O3 for CO methanation reaction

It is still a great challenge to prevent sintering of supported Ni catalysts in highly exothermic reactions. To address this problem, in this work, highly thermal conductive and stable SiC is explored as a Ni catalyst support for CO methanation to produce synthetic natural gas; simultaneously, Al2O3 is utilized to modify the SiC surface to enhance the interaction between the metal and support and restrain the Ni active component from sintering or loss during the reaction. A series of Ni/Al2O3-SiC catalysts were successfully prepared by the co-deposition-precipitation method. The catalysts were investigated by N-2 adsorption, XRD, SEM/EDS, TEM, XPS, H-2-TPR, H-2-TPD and TG. The elemental mapping images indicated that the introduced Al2O3 particles were uniformly deposited on the surface of the SiC support, which evidently enhanced the interaction between Ni and the support by forming Ni-Al2O3 complexes as proved by H-2-TPR results. The Ni/Al2O3-SiC catalyst with an optimal amount of Al2O3 content showed a high catalytic activity and strong resistance to sintering, which can be attributed to two main factors: (1) the addition of Al2O3 can enhance the interactions between Ni and the support, thus inhibiting the migration of Ni particles on the support surface and improving the dispersion of them; (2) the superior heat conductivity of SiC can decrease the generation of hot spots in the catalyst bed.

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.

Preparation of high-surface-area Ni/α-Al2O3 catalysts for improved CO methanation

We have developed a simple approach for the preparation of alpha-Al2O3 with a high surface area (AH) (about 44 m(2) g(-1)) through deposition-precipitation of aluminum nitrate on a carbon black hard template. The AH support was impregnated with a Ni precursor to obtain the Ni/alpha-Al2O3 catalyst (Ni/AH-I). The above catalyst preparation method was further simplified by one-pot co-precipitation of the nickel and aluminum precursors on the carbon template to obtain the AH-supported Ni catalyst (Ni/AH-C). The samples were characterized by nitrogen adsorption, X-ray diffraction, transmission electron microscopy, thermogravimetric analysis, H-2 temperature-programmed reduction and H2 temperature-programmed desorption. The catalytic test results showed that the both Ni/AH-I and Ni/AH-C catalysts exhibited much more enhanced catalytic performance in syngas methanation than a Ni catalyst supported on low-surface-area alpha-Al2O3 at both atmospheric and high pressures, and at a weight hourly space velocity (WHSV) of 30 000 mL g(-1) h(-1), as well as a good stability in a 50 h high-pressure stability test at an extremely high WHSV of 120 000 mL g(-1) h(-1). The test of accelerated aging indicated that Ni/AH-C showed both better hydrothermal stability and stronger resistance to sintering. This work demonstrates AH can be prepared with high feasibility using carbon black as the hard template, and is suitable as a Ni catalyst support for CO methanation.

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.