Anfeng Zhang

Hollow zeolite encapsulated Ni–Pt bimetals for sintering and coking resistant dry reforming of methane

Highly dispersed Ni–Pt bimetallic nanoparticles encapsulated in hollow silicalite-1 single crystals (1.5Ni–0.5Pt@Hol S-1) were a superior catalyst for sintering and coking resistant dry (CO2) reforming of CH4. Large Ni particles loaded on the surface of solid silicalite-1 crystals triggered coke formation, which simultaneously degraded the catalytic activity of small Ni particles. With Ni encapsulated in hollow crystals, the small Ni particles inhibited coke formation. The encapsulating shell prevented coke formed outside from degrading the activity of nickel on the inside, leading to stable high activity even in the presence of carbon. Compared with single metals (Ni or Pt), 1.5Ni–0.5Pt@Hol S-1 enhanced the dispersion of nickel and platinum. In the dry reforming of methane, the 1.5Ni–0.5Pt@Hol S-1 catalyst operated stably under high gaseous hourly space velocity (GHSV = 72 000 ml g−1 h−1) without any inert gas. Only 1.0 wt% carbon deposition was observed by thermogravimetric analysis (TGA) after 6 h of the reaction. Hollow zeolite crystals can reliably support coke resistant catalysts for dry reforming of CH4 and multi-metallic catalysts with well-dispersed nanoparticles.

Solvothermal synthesis of NH2-MIL-125(Ti) from circular plate to octahedron

The MOF material NH2-MIL-125(Ti) was synthesized through the solvothermal method, and the morphology can be controlled by simply modulating the concentration of the reactants during crystallization, which ranges from circular plate through tetragon to octahedron. All samples were characterized by SEM, XRD, FT-IR, UV Raman spectra, TGA, Ar adsorption/desorption and UV-vis spectra. In situ XRD results show that this Ti-incorporated MOF is highly thermostable until 290 °C. It is interesting to find that the light response of NH2-MIL-125(Ti) crystals is closely related to their morphology, and the absorption edges of different morphologies range from 480 nm to 533 nm with band gaps of 2.6 to 2.3 eV, making them potential candidates for photocatalytic applications.

Pd and Pd–CuO nanoparticles in hollow silicalite-1 single crystals for enhancing selectivity and activity for the Suzuki–Miyaura reaction

Pd and Pd–CuO nanoparticles were successfully encapsulated in hollow silicalite-1 single crystals by tetrapropylammonium hydroxide (TPAOH) hydrothermal treatment with an “impregnation-dissolution-recrystallization” process. The size and number of particles in the hollow zeolite depended mainly on the nature of the metal. For palladium, the palladium nanoparticles easily aggregated into larger particles in the hydrothermal process, which displays excellent substrate selectivity for the meta- and para-substituted aryl bromides in the Suzuki–Miyaura reaction. For Pd–CuO binary metals (oxide), introducing copper oxide prevents aggregation of palladium, which shows about 3 times higher activity than encapsulated single Pd catalyst for the above reaction. The strategy using a hollow zeolite crystal as a support is a more reliable method for preparing multi-metallic (oxide) catalysts with well-dispersed nanoparticles.

Hollow Alveolus-Like Nanovesicle Assembly with Metal-Encapsulated Hollow Zeolite Nanocrystals

Inspired by the vesicular structure of alveolus which has a porous nanovesicle structure facilitating the transport of oxygen and carbon dioxide, we designed a hollow nanovesicle assembly with metal-encapsulated hollow zeolite that would enhance diffusion of reactants/products and inhibit sintering and leaching of active metals. This zeolitic nanovesicle has been successfully synthesized by a strategy which involves a one-pot hydrothermal synthesis of hollow assembly of metal-containing solid zeolite crystals without a structural template and a selective desilication-recrystallization accompanied by leaching-hydrolysis to convert the metal-containing solid crystals into metal-encapsulated hollow crystals. We demonstrate the strategy in synthesizing a hollow nanovesicle assembly of Fe2O3-encapsulated hollow crystals of ZSM-5 zeolite. This material possesses a microporous (0.4-0.6 nm) wall of hollow crystals and a mesoporous (5-17 nm) shell of nanovesicle with macropores (about 350 nm) in the core. This hierarchical structure enables excellent Fe2O3 dispersion (3-4 nm) and resistance to sintering even at 800 °C; facilitates the transport of reactant/products; and exhibits superior activity and resistance to leaching in phenol degradation. Hollow nanovesicle assembly of Fe-Pt bimetal-encapsulated hollow ZSM-5 crystals was also prepared.

Effect of SiO2-coating of FeK/Al2O3 catalysts on their activity and selectivity for CO2 hydrogenation to hydrocarbons

SiO2-coated FeK/Al2O3 catalysts with different silica content were prepared and examined for the synthesis of hydrocarbons from CO2 hydrogenation. It was found that SiO2 coating affects both the activity for CO2 conversion and the selectivity to higher hydrocarbons, depending on the loading level. The catalyst with 9 wt% SiO2 coating showed both high CO2 conversion (63%) and high selectivity toward C2+ hydrocarbons (74%), while further higher coating led to suppression of catalyst activity. The analytical characterization of SiO2-coated catalysts confirmed the interactions of SiO2–Fe and SiO2–Al2O3, which largely reduced the metal–support interaction and decreased the reduction temperature of iron oxide. In addition, an increase of adsorption capacity for CO was observed with desired SiO2 coating. It is likely that SiO2-coating improved the catalyst hydrophobic property, thereby reducing the negative impact of water by-product and facilitating the reverse water gas shift reaction and subsequent hydrogenation towards higher CO2 conversion to higher hydrocarbons.

Efficient synthesis and sulfonation of ordered mesoporous carbon materials

Ordered mesoporous carbons (OMCs) with hexagonal structure were efficiently synthesized via cooperative self-assembly of phenol/formaldehyde resol and surfactant F127 under acidic aqueous conditions. Induced by HCl, a gel phase mainly containing phenol/formaldehyde resol and F127 was obtained within several hours. X-ray diffraction (XRD), transmission electron microscope (TEM) and nitrogen adsorption isotherms indicated that the synthesized samples possess 2-D hexagonal mesostructure. The influence of the synthesis conditions, including acid concentration and mass ratio of resol to F127, was investigated. When the acid concentration was fixed in the range of 0.6-2.0 M and the mass ratio of resol to F127 in the range of 3.5-4.0, highly ordered mesoporous carbon could be synthesized. The synthesized OMCs could be easily sulfonated in concentrated sulfuric acid at elevated temperature. The results indicate that the mesostructural stability and the content of the surface sulfonic acid (SO(3)H) groups depend mainly on the pyrolysis temperature of the OMCs and the sulfonation temperature, suggesting that the combination of pyrolysis and sulfonation temperature is essential for developing OMCs with high densities of SO(3)H groups.

二次法（同晶取代）快速合成Sn-β沸石用于葡萄糖异构制果糖

Sn-beta zeolites were facilely synthesized by a post-synthesis method consisting of two steps, i.e., heteroatom removal and isomorphous substitution by reaction with sncl4. this significantly shortened the sn-beta zeolite preparation time from the previously reported 40 d to less than 1 d. it was shown that sn-beta samples prepared using the post-synthesis method had higher sn contents than that prepared using a hydrothermal method. the as-synthesized sn-beta zeolites were tested in the isomerization of glucose to fructose in aqueous media. the effects of reaction temperature, reaction time, catalyst amount, solvent, and halide additive on the isomerization reaction over sn-al-beta zeolites were studied in detail. under the optimized conditions, the yield of fructose reached a maximum of similar to 43%. the catalysts can be reused without loss of activity after regeneration by calcination. (c) 2014, dalian institute of chemical physics, chinese academy of sciences. published by elsevier b.v. all rights reserved.

A facile strategy for enhancing FeCu bimetallic promotion for catalytic phenol oxidation

The mesoporous ZSM-5 zeolite obtained from alkaline treatment was found to be a superior support of bimetallic FeCu, minimizing the nanoparticle size, enhancing the bimetallic interaction, and promoting catalytic oxidation of phenol. The physicochemical characteristics of the as-prepared FexCuy/ZSM-5 samples were evaluated by XRD, TEM, Ar adsorption, H2-TPR, and 57Fe Mossbauer spectroscopy which revealed a strong bimetallic interaction. Meanwhile, phenol oxidation was applied as a probe reaction under mild conditions. By supporting FeCu bimetallic oxides on mesoporous ZSM-5, the obtained Fe5Cu5/ME displayed the highest activity, which can be attributed to both the minimized nanoparticle size and the enhanced bimetallic interaction. The mesoporous ZSM-5 support used in this work was obtained from alkaline treatment, which led to a rough mesoporous surface. This surface sufficiently enhanced the dispersion and prohibited metal migration, therefore preventing nanoparticle aggregation and enhancing the bimetallic interaction. The strategy of using mesoporous ZSM-5 obtained from alkaline treatment as a support is a reliable method for preparing multi-metallic catalysts with well-dispersed nanoparticles.

Facile synthesis of zeolite-encapsulated iron oxide nanoparticles as superior catalysts for phenol oxidation

Meso-ZSM-5 modified by polyethyleneimine has been found to be an excellent support for iron oxide with improved physicochemical properties of iron oxide particles including size and chemical state. The resulting ZSM-5 encapsulated iron nanoparticles exhibit superior catalytic activity for phenol oxidation.

Facile one-step synthesis of hierarchical porous carbon monoliths as superior supports of Fe-based catalysts for CO2 hydrogenation

A versatile strategy involving one-step desilication of coke-deposited spent zeolite catalyst was successfully developed to prepare hierarchical porous carbon monoliths (HPCMs). Such a strategy avoids the use of hard or soft templates and carbon sources, eliminates high temperature carbonization, simultaneously minimizing the emissions from processing spent catalysts. The resulting carbon exhibits a controlled morphology such as three-dimensional networks, hollow spheres or nanosheets, a high degree of graphitization and a multi-level porous structure. Its mesopore (2–50 nm) surface area can reach 522 m2 g−1 and both mesopore and macropore (50–350 nm) volumes are more than 1.0 cm3 g−1. Such hierarchical porous carbon was found to be a superior support for minimizing the nanoparticle size and enhancing the synergism of the Fe–K catalyst for promoting CO2 hydrogenation. Using such a catalyst results in increased conversion of carbon dioxide and enhanced selectivity of high value olefins (C2–4) and long-chain hydrocarbons (C5+).