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Proposed “dissolve and precipitate” reaction mechanism of WO3–STS catalyzed MO oxidative cleavage reaction.

Iron promotes the chemical equilibrium of the dealumination process by inducing the mobility and agglomeration of extra-framework aluminum, and further facilitates the formation of sillimanite at a lower temperature of 1000 °C.

Proton exchange membrane fuel cells (PEMFCs) are regarded as one of the promising new carbon mitigation strategies to realize carbon neutrality. However, efficient and robust electrocatalysts are vital for the commercialization of PEMFCs. Herein, three commercial Pt/C electrocatalysts were investigated including a carbon support and Pt nanoparticles (NPs) to identify their merits and disadvantages, which will help end users quickly select catalysts with excellent performances among the many brands of domestic and foreign catalysts to further better study and better utilize them. Subsequently, they were optimized for real automotive application for about 1800 h, and then the variations in the electrocatalysts on the MEA were analysed by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The mean Pt particle size of the catalysts after operating for 1800 h (cathode, 9.9 ± 3.2 nm) was nearly 4-fold that before use (2.5 ± 0.6 nm), greatly reducing the exposure of metal sites, which was due to the violent three-phase interfacial reaction (ORR) occurring at the cathode side. Also, this assertion was supported by the negative shift in the Pt 4f peaks in the XPS spectra. Moreover, to determine the coalescent evolution of the Pt particles, an

Rational design and fabrication of hierarchical zeolites with desired structures has long been of essential and practical interest to engineers and scientists. Featuring a hierarchical nano-shell and enclosed interior space, hollow nano ZSM-5 crystals exhibit excellent capability as the key catalyst in various important reactions. However, it has been an ever-increasing but challenging task to directly fabricate hierarchical hollow Al-rich nano ZSM-5 crystals since only limited mesoporosity in ZSM-5 zeolites with Si/Al < 15 can be generated by desilication. Here, a one-step Al-distribution regulated desilication approach combining the synthesis of an Al-rich parent ZSM-5 (Si/Al = 12.5) with locally concentrated Al (LCA) domains and a simple alkali-treatment step is presented. The existence of LCA domains and their impacts on the selective desilication process were validated by diffuse reflectance UV spectroscopy and filtrate analysis, and approximately 49% of Al atoms emerged in Z5-LCA samples as Al species in close contact. Compared with its parent zeolite, the hierarchical hollow nano ZSM-5 crystal exhibited increased catalytic activities as well as ∼2-fold improved selectivities for high-value light olefins (C2H4 and C3H6) in the catalytic cracking of decalin (a model bulky naphthene molecule) and a real naphtha feedstock. These findings expand our knowledge on achieving desirable zeolite structures by regulating framework Al distribution, and suggest a promising new catalyst toward highly selective production of light olefins from naphthene feedstocks.

A tungsten containing catalyst catalyzed oxidative cleavage of methyl oleate (MO) by employing H

Titanium silicalite-1 (TS-1) has been shown to be a heterogeneous catalyst with remarkable efficiency and selectivity; however, the nature of the active Ti site in the MFI framework remains elusive. Here we report combined experimental and theoretical research on Ti distribution in the 12 crystallographically distinct T sites of the MFI framework in high-Ti-loaded TS-1 (2.7 wt % in TiO2). Using a multishell fit to extended X-ray absorption fine structure, we show that T4 is the most populated site, in marked contrast to the preferential substitution sites and the definitely excluded sites assumed hitherto by diffraction studies. The identification is supported by a good agreement between calculated and experimental X-ray absorption near-edge structure studies and by full periodic density functional theory (DFT) computation. In spite of having the identical most favored site, the preference order for the remaining sites predicted by DFT does not fully match the experimental results. This suggests that Ti d...

Commercial deactivated HTS zeolite has been investigated by multiple characterization methods and catalytic evaluations. These indicate that structural and textural properties are not mainly ascribed to the irreversible deactivation, but some framework Ti species are transformed into Ti-rich nanoparticles. Both Bronsted and Lewis acid sites are observed in deactivated HTS zeolite, which agrees well with the spectroscopic characterization results and Tanabe’s acidity theory on mixed binary oxides. Hence the acidic Ti-rich aggregates are attributed to the amorphous TiO2–SiO2 nanoparticles located on the external surface of the zeolite. Furthermore, it is demonstrated that the catalytic performance of deactivated HTS zeolite in phenol hydroxylation is seriously dependent on its acidity properties, which can accelerate the decomposition of H2O2. As a consequence, we conclude that the irreversible deactivation of HTS zeolite in the ammoximation process is caused by the formation of acidic amorphous TiO2–SiO2 nanoparticles catalyzing the fast H2O2 decomposition reaction.

The effects of two Al2O3 phases, γ- and θ-Al2O3, and Cl component on the performances of Pt-Al2O3 catalysts in the dehydrogenation of propane were investigated in this work. The catalysts were systematically characterized by various techniques, such as scanning transmission electron microscopy (STEM), temperature-programmed desorption with ammonia as probe molecules (NH3-TPD) and temperature-programmed oxidation (TPO). The characterizations and catalytic results show that: (i) the pore structures and acid properties of the two Al2O3 phases can change the quantity, location and property of the carbon deposition, (ii) the existence of Cl plays a significant role on the agglomeration of Pt particles and carbon deposition, which further influence the catalytic performances of Pt-Al2O3 catalysts with different support phases for propane dehydrogenation.

Well-crystallized hexagonal NiS and rhombohedral Ni3S2 microcrystallines on spent S Zorb adsorbent were detected and verified by HRTEM for the first time. The depth distributions of different Ni species from surface to subsurface were elucidated via XPS combined with cluster argon ion sputtering. NiS and Ni3S2 are stable intermediate products rather than transition states during the desulfurization process. The results would provide important contributions to furthering the investigation on the desulfurization mechanism for the Ni/ZnO adsorbents.

The microstructure of air-sensitive Raney-type catalysts directly determines their activity and selectivity for a catalytic reaction. The fine structure of a rapidly quenched Ni-Al alloy doped with Fe and Cr (RQ Ni-Al-FC) was investigated by electron microscopy imaging and spectroscopic techniques, and its structure was successfully characterized by using a vacuum transfer holder in the transmission electron microscope. The microstructural comparison of pristine and passivated/combusted samples was discussed in detail. This work provides the structure of RQ Ni-Al based catalysts as a contribution to exploring their synthesis-structure-performance relationship.

The transformation from NaA (LTA) to MCM-49 (MWW) zeolite was achieved in the synergism of hexamethyleneimine (HMI), NaOH, and SiO2, in spite of no common composite build units between LTA (lta, sod, and d4r) and MWW (mel and d6r) structure. NaA (SiO2/Al2O3 = 2.0) was employed as the parent zeolite. The samples prepared at different crystallization stages were characterized by XRD, SEM, 29Si/27Al/13C MAS NMR, and STEM-EDS to investigate the intermediates during the transformation from NaA to MCM-49. As shown in SEM and STEM-EDS images, MCM-49 was proposed to be transformed gradually from the exterior to the interior of NaA, which was clearly observed by the core (LTA, low SiO2/Al2O3)–shell (MWW, high SiO2/Al2O3) coexisting zeolites as intermediates. With high relative crystallinity and the uniform sizes of crystals, the final MCM-49 was featured by Si enrichment on the external surface, which was proved by the shell (SiO2/Al2O3 = 45.4) wrapping around the core (SiO2/Al2O3 = 22.0). For transformed H-MCM-49...

Precisely controlling the microstructure and composition of each component in hybrid nanomaterials is critical for desired properties but very challenging. Herein, we demonstrate a new proof-of-concept method, or microtubing-based simple-programmed microfluidic processes (MT-SPMPs). MT-SPMPs preserve the ability for controlled hybridization by accurately adjusting the detailed microstructures and crystal phases of components using Sn–SnO2 nanoparticles as models, by coupling the synergistic effects of complex surfactants with the precise reaction kinetics control. Consequently, uniform Sn–SnO2 nanospheres with diameters from 2 nm to 14 nm or Sn@SnO2 nanorods with a diameter of 19 nm and length of 66 nm can be achieved. The SnO2 shell thickness can be well controlled at the Bohr exciton radius range. Particularly, the defect type and density in these nanospheres and nanorods can be tuned for unique ultraviolet emission at 347 nm or enhanced blue emission at 475 nm. Analysis on the detailed microstructure and crystal-phase dependent photoluminescences indicates that the quantum mechanical dipole-forbidden rule can be effectively conquered by the formation of Sn–SnO2 nanohybrids with controlled defects (oxygen vacancies or Sn interstitials).

Atom-resolved microstructure variations and deactivation effects on the commercial NiMo/&gamma, Al2O3 catalysts were revealed by aberration-corrected scanning transmission electron microscope (Cs-STEM) equipped with enhanced energy dispersive X-ray spectroscopy (EDS). Structural information parallel to and vertical to the electron beam provides definitive insight toward an understanding of structure&ndash, activity relations. Under the mild to harsher reaction conditions, &ldquo, fragment&rdquo, structures (like metal single atoms, metal clusters, and nanoparticles) of commercial NiMo/&gamma, Al2O3 catalysts, gradually reduces, while MoS2 nanoslabs get longer and thinner. Such a result about active slabs leads to the reduction in the number of active sites, resulting in a significant decrease in activity. Likewise, the average atomic ratio of promoter Ni and Ni/(Mo + S) ratio of slabs decrease from 2.53% to 0.45% and from 0.0788 to 0.0326, respectively, by means of EDS under the same conditions stated above, reflecting the weakening of the promotional effect. XPS result confirms the existence of NixSy species in deactivated catalysts. This could be ascribed to the Ni segregation from active phase. Furthermore, statistical data give realistic coke behaviors associated with the active metals. With catalytic activity decreasing, the coke on the active metals regions tends to increase faster than that on the support regions. This highlights that the commercial NiMo/&gamma, Al2O3 catalyst during catalysis is prone to produce more coke on the active metal areas.

The propagation of memes on online social networks often depends on the mechanism of social affirmation. Centola termed such social-affirmation-driven diffusion as complex contagion and partly validated it through an online experiment. However, for actual online meme propagation, the mechanism of social affirmation often takes effect in combination with various other factors and mechanisms. In this paper, we examine the combinatorial effects of social affirmation and the attractiveness and persistence of the meme by proposing and analyzing a UACI model, where an agent’s activities to receive and transfer a meme is associated with the transition between its four possible states of “Uninformed”, “Attended”,“Convinced” and “Immune”. The numerical simulations illustrate nontrivial patterns of propagation. Especially, it is revealed that the effects of simple and complex contagions co-exist and equilibrate in accordance with the joint functions of meme attractiveness and social affirmation. Furthermore, the low-persistence of the meme hinders the propagation-scale more remarkably on the regular network than on the random one, indicating that the persistence may be critical for retaining complex contagion.