A Facile Strategy to Prepare Shaped ZSM-5 Catalysts with Enhanced Para-Xylene Selectivity and Stability for Toluene Methylation: The Effect of In Situ Modification by Attapulgite.

A general strategy for preparing shaped toluene methylation catalysts with enhanced para-selectivity and stability is developed by extruding ZSM-5 zeolite with attapulgite as a binder. The novel attapulgite/ZSM-5 extrudate exhibited significantly higher para-selectivity and stability in comparison to the conventional alumina-bound ZSM-5 extrudate. The catalyst samples have been characterized by in situ X-ray diffraction, scanning electron microscope (SEM), NH3 temperature programmed desorption (TPD), thermogravimetric analysis (TGA) as well as n-hexane/cyclohexane physical adsorption. The enhanced catalytic performance of attapulgite/ZSM-5 extrudate is correlated with the in-situ modification of acid sites in the catalyst by mobile alkaline species, which is introduced via extrusion with attapulgite. Moreover, a higher para-selectivity was obtained over attapulgite-bound modified ZSM-5 extrudate. Such facile and universal strategy of extruding ZSM-5 catalysts with attapulgite as binder could pave a way for preparation of shaped zeolite-base catalyst with enhanced catalytic performance.

Dynamic structural evolution of iron catalysts involving competitive oxidation and carburization during CO2 hydrogenation.

Identifying the dynamic structure of heterogeneous catalysts is crucial for the rational design of new ones. In this contribution, the structural evolution of Fe(0) catalysts during CO2 hydrogenation to hydrocarbons has been investigated by using several (quasi) in situ techniques. Upon initial reduction, Fe species are carburized to Fe3C and then to Fe5C2. The by-product of CO2 hydrogenation, H2O, oxidizes the iron carbide to Fe3O4. The formation of Fe3O4@(Fe5C2+Fe3O4) core-shell structure was observed at steady state, and the surface composition depends on the balance of oxidation and carburization, where water plays a key role in the oxidation. The performance of CO2 hydrogenation was also correlated with the dynamic surface structure. Theoretical calculations and controll experiments reveal the interdependence between the phase transition and reactive environment. We also suggest a practical way to tune the competitive reactions to maintain an Fe5C2-rich surface for a desired C2+ productivity.

Effects of mechanical and chemical control on invasive Spartina alterniflora in the Yellow River Delta, China.

Spartina alterniflora is one of the most noxious invasive plants in China and many other regions. Exploring environmentally friendly, economic and effective techniques for controlling Spartina alterniflora is of great significance for the management of coastal wetlands. In the present study, different approaches, including mowing and waterlogging, mowing and tilling and herbicide application, were used to control Spartina alterniflora. The results suggest that the integrated approach of mowing and waterlogging could eradicate Spartina alterniflora, the herbicide haloxyfop-r-methyl could kill almost all the Spartina alterniflora, and the integrated approach of mowing and tilling at the end of the growing season was a perfect way to inhibit the germination of Spartina alterniflora in the following year. However, no matter which control approach is adopted, secondary invasion of Spartina alterniflora must be avoided. Otherwise, all the efforts will be wasted in a few years.

Statistical study of ductility-dip cracking induced plastic deformation in polycrystalline laser 3D printed Ni-based superalloy.

Ductility-dip cracking in Ni-based superalloy, resulting from heat treatment, is known to cause disastrous failure, but its mechanism is still not completely clear. A statistical study of the cracking behavior as a function of crystal orientation in a laser 3D-printed DL125L Ni-based superalloy polycrystal is investigated here using the synchrotron X-ray microdiffraction. The dislocation slip system in each of the forty crystal grains adjacent to the 300 µm long crack has been analyzed through Laue diffraction peak shapes. In all these grains, edge-type geometrically necessary dislocations (GNDs) dominate, and their dislocation line directions are almost parallel to the crack plane. Based on Schmid's law, the equivalent uniaxial tensile force direction is revealed normal to the trace of the crack. A qualitative mechanism is thus proposed. Thermal tensile stress perpendicular to the laser scanning direction is elevated due to a significant temperature gradient, and thus locations in the materials where the thermal stress exceeds the yield stress undergo plastic deformation mediated by GND activations. As the dislocations slip inside the crystal grains and pile up at the grain boundaries, local strain/stress keeps increasing, until the materials in these regions fail to sustain further deformation, leading to voids formation and cracks propagation.

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.

Real-time microstructure imaging by Laue microdiffraction: A sample application in laser 3D printed Ni-based superalloys.

Synchrotron-based Laue microdiffraction has been widely applied to characterize the local crystal structure, orientation, and defects of inhomogeneous polycrystalline solids by raster scanning them under a micro/nano focused polychromatic X-ray probe. In a typical experiment, a large number of Laue diffraction patterns are collected, requiring novel data reduction and analysis approaches, especially for researchers who do not have access to fast parallel computing capabilities. In this article, a novel approach is developed by plotting the distributions of the average recorded intensity and the average filtered intensity of the Laue patterns. Visualization of the characteristic microstructural features is realized in real time during data collection. As an example, this method is applied to image key features such as microcracks, carbides, heat affected zone, and dendrites in a laser assisted 3D printed Ni-based superalloy, at a speed much faster than data collection. Such analytical approach remains valid for a wide range of crystalline solids, and therefore extends the application range of the Laue microdiffraction technique to problems where real-time decision-making during experiment is crucial (for instance time-resolved non-reversible experiments).

Size-controlled silver nanoparticles stabilized on thiol-functionalized MIL-53(Al) frameworks.

A postsynthetic modification method was used to prepare thiol-functionalized metal-organic frameworks (MOFs) by the amidation of mercaptoacetic acid with the amine group, which is present in the frameworks of NH2-MIL-53(Al). By doing this, the thiol group has been successfully grafted on the MOF, which perfectly combined the highly developed pore structures of the MOF with the strong coordination ability of the thiol group. The resulting thiol-functionalized MIL-53(Al) showed a significantly high adsorption capacity for heavy metal ions like Ag(+) (182.8 mg g(-1)). Even more importantly, these grafted thiol groups can be used as anchoring groups for stabilizing metal nanoparticles (NPs) with controllable sizes. Taking silver as an example, monodispersed Ag NPs encapsulated in the cages of MIL-53(Al) have been prepared by using a two-step procedure. In addition, the particle size of the Ag NPs was adjustable to some extent by controlling the initial loading amount. The average size of the smallest Ag NPs is 3.9 ± 0.9 nm, which is hard to obtain for Ag NPs because of their strong tendency to aggregate.

A synchrotron study of microstructure gradient in laser additively formed epitaxial Ni-based superalloy.

Laser additive forming is considered to be one of the promising techniques to repair single crystal Ni-based superalloy parts to extend their life and reduce the cost. Preservation of the single crystalline nature and prevention of thermal mechanical failure are two of the most essential issues for the application of this technique. Here we employ synchrotron X-ray microdiffraction to evaluate the quality in terms of crystal orientation and defect distribution of a Ni-based superalloy DZ125L directly formed by a laser additive process rooted from a single crystalline substrate of the same material. We show that a disorientation gradient caused by a high density of geometrically necessary dislocations and resultant subgrains exists in the interfacial region between the epitaxial and stray grains. This creates a potential relationship of stray grain formation and defect accumulation. The observation offers new directions on the study of performance control and reliability of the laser additive manufactured superalloys.

Synthesis of yolk-shell HPW@Hollow silicalite-1 for esterification reaction.

HPW@Hollow S-1, a novel solid catalyst which can be reused in the synthesis of ethyl acetate, was successfully prepared by the ship-in-bottle approach. The catalyst simultaneously shows high activity that resembles homogeneous catalysts, and outstanding stability like that of heterogeneous catalysts.

Size- and morphology-controlled NH2-MIL-53(Al) prepared in DMF-water mixed solvents.

We present here a simple solvothermal method to fabricate metal-organic framework NH2-MIL-53(Al) crystals with controllable size and morphology just by altering the ratio of water in the DMF-water mixed solvent system without the addition of any surfactants or capping agents. With increasing the volume ratio of water in the mixed solvents, a series of NH2-MIL-53(Al) crystals with different sizes and morphologies were synthesized. The average size of the smallest crystal is 76 ± 20 nm, which provides us a simple and environmentally friendly way to prepare nanoscale MOFs. The largest BET surface area of these samples is 1882 m(2) g(-1) that is mainly contributed by its micropore surface area, and its corresponding micropore volume is 0.83 cm(3) g(-1), which have greatly extended its application in the fields of gas adsorption and postsynthetic modification. All these samples were characterized by SEM, XRD, N2 adsorption/desorption, TGA and FT-IR. Then a mechanism for the impact of the water ratio on the crystal size and morphology is presented and discussed.

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.