Discerning the Role of Ag–O–Al Entities on Ag/γ-Al₂O₃ Surface in NOx Selective Reduction by Ethanol

Alumina-supported silver catalysts (Ag/Al₂O₃) derived from AlOOH, Al­(OH)₃, and Al₂O₃ were investigated for the selective catalytic reduction of NOx by ethanol. In order to discern the role of support Al skeleton in anchoring silver species and reducing NOx, the series of alumina-supported silver catalysts calcined at different temperatures was characterized by means of <i>in situ</i> DRIFTS, XPS, UV–vis DRS, XRD, BET, and NMR. It was found that the NO_<i>x</i> reduction efficiency order as affected by alumina precursors could be generally described as AlOOH > Al₂O₃ ≫ Al­(OH)₃, with the optimum calcination temperature of 600 °C. XPS and UV–vis results indicated that silver ions predominated on the Ag/Al₂O₃ surface. Solid state NMR suggested that the silver ions might be anchored on Al tetrahedral and octahedral sites, forming Ag–O–Al_tetra and Ag–O–Al_octa entities. With the aid of NMR and DFT calculation, Al_octa was found to be the energetically favorable site to support silver ions. However, DFT calculation indicated that the Ag–O–Al_tetra entity can significantly adsorb and activate vital −NCO species rather than the Ag–O–Al_octa entity. A strongly positive correlation between the amount of Al_tetra structures and N₂ production rate confirms the crucial role of Al_tetra in NOx reduction by ethanol

Significant Enhancement of Thermal Conductivity in Polymer Composite via Constructing Macroscopic Segregated Filler Networks

The low efficiency of thermal conductive filler is an unresolved issue in the area of thermal conductive polymer composites. Although it is known that minimizing phonon or electron interfacial scattering is the key for achieving high thermal conductivity, the enhancement is generally limited by preparation methods that can yield the ideal morphology and interfaces. Herein, low temperature expandable graphite (LTEG) is added into a commercial impact modifier (Elvaloy4170), which is then coated onto poly­(butylene terephthalate) (PBT) particles with various sizes at millimeter scale between their melting temperatures. Thus, macroscopic segregated filler networks with several considerations are constructed: high LTEG loading leads to a short distance between fillers and a robust filler network; continuous Elvaloy-LTEG phase leads to a continuous filler network; and good interaction among filler and matrix leads to good interfacial interaction. More importantly, the rather large size of PBT particles provides the filler networks with low specific interfacial area, which minimizes the interfacial scattering of phonons or electrons. Relative to homogeneous composites with an identical composition, the thermal conductivity is enhanced from 6.2 to 17.8 W/mK. Such an enhancement span is the highest compared with results reported in the literature. Due to possible “shortcut” behavior, much higher effectiveness can be achieved for the current system than found in literature results when the Elvaloy-LTEG phase is considered as filler, with the effectiveness even exceeding the upper limit of theoretical calculation for highly loaded Elvaloy-LTEG phase with relatively large PBT particle sizes. This could provide some guidelines for the fabrication of highly thermal conductive polymer composites as well as multifunctional polymer composites

Formation of Conductive Networks with Both Segregated and Double-Percolated Characteristic in Conductive Polymer Composites with Balanced Properties

Morphological control of conductive networks involves the construction of segregated or double-percolated conductive networks is often reported to reduce the electrical percolation threshold of conductive polymer composites (CPCs) for better balance among electrical conductivity, mechanical properties, and filler content. Herein, the construction of conductive networks with both segregated and double-percolated characteristics is achieved based on polypropylene (PP)/polyethylene (PE) and multi-wall carbon nanotubes (CNTs). CNTs were firstly dispersed in PE; then PE/CNTs were compounded with PP particles well below the melting temperature of PP. It is observed that the percolation threshold (<i>p</i>_c) decreases with increasing PP particle size (size 3.6 mm, <i>p</i>_c = 0.08 wt %), which agrees with previous theoretical prediction and experiment in much smaller particle size range. To further study this, the amount of CNTs in PE is varied. It is shown that the degree of PE/CNTs coating on PP particles varies with CNTs as well as PE content in these composites, and have significant influence on the final electrical property. Furthermore, a model combines classical percolation theory and model for segregated network has been proposed to analyze the effect of particle size, degree of coating and thickness of coating on the percolation behavior of these CPCs. In such a model the percolation of CNTs in PE phase as well as PENT phase in the segregated structure can be described. Overall, through such method, a much better balance among mechanical property, conductivity, and filler content is achieved in these CPCs comparing with the results in literature

Asymmetric Construction of 3‑Azabicyclo­[3.1.0]­hexane Skeleton with Five Contiguous Stereogenic Centers by Cu-Catalyzed 1,3-Dipolar Cycloaddition of Trisubstituted Cyclopropenes

A highly diastereo- and enantioselective desymmetrization of prochiral cyclopropenes via a Cu­(CH₃CN)₄BF₄/Ph-Phosferrox complex catalyzed 1,3-dipolar cycloaddition of azomethine ylides was described. A variety of complex 3-azabicyclo­[3.1.0]­hexane derivatives bearing five contiguous stereogenic centers and two all-carbon quaternary stereogenic centers were directly synthesized as a single isomer in excellent yields (up to 99%) and enantioselectivities (97 → 99% ee). Notably, various functional groups (CO₂R, CN, CONMe₂, and Ph) of cyclopropenes were found to be well-tolerated in this transformation. The cycloadduct was conveniently converted to a biologically important GABA derivative via LiAlH₄ reduction and subsequent hydrolysis

Interactive Effect for Simultaneous Removal of SO₂, NO, and CO₂ in Flue Gas on Ion Exchanged Zeolites

A purification system for simultaneous removal of SO₂, NO, and CO₂ in flue gas was considered in this study. For improving the purification performance of candidate adsorbent NaX zeolite, ion exchange experiments were conducted with cation K⁺, Ca²⁺, Mn²⁺, and Co²⁺, respectively. The texture properties of series zeolites were examined by N₂ porosimetry, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analyses. Among the sorbents investigated, K–NaX zeolite exhibited the best result to remove SO₂, NO, and CO₂ all together. XPS results revealed that SO₂ has been oxidized to form SO₄^2– on the solid surface; however, species N and C have not been observed. In order to understand the coadsorption effects, pure component, binary, ternary components, and mimic flue gas breakthrough experiments were designed and carried out. It suggested that SO₂ and NO was bonded on the adsorbent surface with degradation of NO. A little competitive effect of CO₂ on SO₂ and NO adsorption system were found. Finally, monitoring of coadsorption venting gas, thermodynamic equilibrium species simulation, TPD experiment, and quantum chemical calculation technology were used to examine the interactive effect

β‑Silyl Acrylates in Asymmetric [3 + 2] Cycloadditions Affording Pyrrolidine Azasugar Derivatives

A highly efficient copper­(I)-catalyzed asymmetric 1,3-dipolar cycloaddition of azomethine ylides with 3-silyl unsaturated esters has been developed, providing elegant access to chiral 3-silylpyrrolidine derivatives bearing contiguous stereogenic centers in moderate-to-excellent yields (up to 99%) with high diastereo- and enantioselectivities (dr up to >99:1; ee up to 96%). Notably, the 3-silylpyrrolidines can easily be converted to pyrrolidine azasugar derivatives with potential biological activities by the reduction of two ester groups and carbon–silicon bond oxidation

Mechanism of Thermal Adaptation in the Lactate Dehydrogenases

The mechanism of thermal adaptation of enzyme function at the molecular level is poorly understood but is thought to lie within the structure of the protein or its dynamics. Our previous work on pig heart lactate dehydrogenase (phLDH) has determined very high resolution structures of the active site, via isotope edited IR studies, and has characterized its dynamical nature, via laser-induced temperature jump (T-jump) relaxation spectroscopy on the Michaelis complex. These particular probes are quite powerful at getting at the interplay between structure and dynamics in adaptation. Hence, we extend these studies to the psychrophilic protein cgLDH (<i>Champsocephalus gunnari</i>; 0 °C) and the extreme thermophile tmLDH (<i>Thermotoga maritima</i> LDH; 80 °C) for comparison to the mesophile phLDH (38−39 °C). Instead of the native substrate pyruvate, we utilize oxamate as a nonreactive substrate mimic for experimental reasons. Using isotope edited IR spectroscopy, we find small differences in the substate composition that arise from the detailed bonding patterns of oxamate within the active site of the three proteins; however, we find these differences insufficient to explain the mechanism of thermal adaptation. On the other hand, T-jump studies of reduced β-nicotinamide adenine dinucleotide (NADH) emission reveal that the most important parameter affecting thermal adaptation appears to be enzyme control of the specific kinetics and dynamics of protein motions that lie along the catalytic pathway. The relaxation rate of the motions scale as cgLDH > phLDH > tmLDH in a way that faithfully matches <i>k</i>_cat of the three isozymes

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Morphology Evolution of Polymer Blends under Intense Shear During High Speed Thin-Wall Injection Molding

The morphology evolution under shear during different processing is indeed an important issue regarding the phase morphology control as well as final physical properties of immiscible polymer blends. High-speed thin wall injection molding (HSTWIM) has recently been demonstrated as an effective method to prepare alternating multilayered structure. To understand the formation mechanism better and explore possible phase morphology for different blends under HSTWIM, the relationship between the morphology evolution of polymer blends based on polypropylene (PP) under HSTWIM and some intrinsic properties of polymer blends, including viscosity ratio, interfacial tension, and melt elasticity, is systematically investigated in this study. Blends based on PP containing polyethylene (PE), ethylene vinyl alcohol copolymer (EVOH), and polylactic acid (PLA) are used as examples. Compatibilizer has also been added into respective blends to alter their interfacial interaction. It is demonstrated that dispersed phase can be deformed into a layered-like structure if interfacial tension, viscosity ratio, and melt elasticity are relatively small. While some of these values are relatively large, these dispersed droplets are not easily deformed under HSTWIM, forming ellipsoidal or fiber-like structure. The addition of a moderate amount of compatibilizer into these blends is shown to be able to reduce interfacial tension and the size of dispersed phase, thus, allowing more deformation on the dispersed phase. Such a study could provide some guidelines on phase morphology control of immiscible polymer blends under shear during various processing methods

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