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Seakweng Vong Chenyang Shi Pin Lyu 《Numerical Methods for Partial Differential Equations》2019,35(2):493-508
Second order finite difference schemes for fractional advection–diffusion equations are considered in this paper. We note that, when studying these schemes, advection terms with coefficients having the same sign as those of diffusion terms need additional estimates. In this paper, by comparing generating functions of the corresponding discretization matrices, we find that sufficiently strong diffusion can dominate the effects of advection. As a result, convergence and stability of schemes are obtained in this situation. 相似文献
496.
AbstractOne new coumarin, muralatin R, was isolated from the leaves of Murraya alata Drake (Rutaceae). Its structure was elucidated by extensive analysis of the NMR and MS data, along with the specific rotation comparison. Muralatin R was found to be capable of activating the transient receptor potential vanilloid 1 (TRPV1) channel through desensitization mechanism. The results supply reference for clarification of the therapeutic basis and mechanism of action of Murraya plants for treating psychogenic pain or somatoform pain disorders. 相似文献
497.
Mu Xiao Lei Zhang Bin Luo Miaoqiang Lyu Zhiliang Wang Hengming Huang Songcan Wang Aijun Du Lianzhou Wang 《Angewandte Chemie (International ed. in English)》2020,59(18):7230-7234
Atomic co‐catalysts offer high potential to improve the photocatalytic performance, of which the preparation with earth‐abundant elements is challenging. Here, a new molten salt method (MSM) is designed to prepare atomic Ni co‐catalyst on widely studied TiO2 nanoparticles. The liquid environment and space confinement effect of the molten salt leads to atomic dispersion of Ni ions on TiO2, while the strong polarizing force provided by the molten salt promotes formation of strong Ni?O bonds. Interestingly, Ni atoms are found to facilitate the formation of oxygen vacancies (OV) on TiO2 during the MSM process, which benefits the charge transfer and hydrogen evolution reaction. The synergy of atomic Ni co‐catalyst and OV results in 4‐time increase in H2 evolution rate compared to that of the Ni co‐catalyst on TiO2 prepared by an impregnation method. This work provides a new strategy of controlling atomic co‐catalyst together with defects for efficient photocatalytic water splitting. 相似文献
498.
Pedro Laborda Yong‐Mei Lyu Fabio Parmeggiani Ai‐Min Lu Wen‐Jiao Wang Ying‐Ying Huang Kun Huang Juan Guo Li Liu Sabine L. Flitsch Josef Voglmeir 《Angewandte Chemie (International ed. in English)》2020,59(13):5308-5311
Chitin is one of the most abundant and cheaply available biopolymers in Nature. Chitin has become a valuable starting material for many biotechnological products through manipulation of its N‐acetyl functionality, which can be cleaved under mild conditions using the enzyme family of de‐N‐acetylases. However, the chemoselective enzymatic re‐acylation of glucosamine derivatives, which can introduce new stable functionalities into chitin derivatives, is much less explored. Herein we describe an acylase (CmCDA from Cyclobacterium marinum) that catalyzes the N‐acylation of glycosamine with a range of carboxylic acids under physiological reaction conditions. This biocatalyst closes an important gap in allowing the conversion of chitin into complex glycosides, such as C5‐modified sialosides, through the use of highly selective enzyme cascades. 相似文献
499.
Cu-ZnO is broadly used as a catalyst in CO2 reduction to produce methanol, but fabricating small-sized Cu-ZnO catalysts with strong Cu-ZnO interactions remains a challenge. In this work, a simple, low-cost method is proposed to synthesize small-sized Cu-ZnO/SiO2 with high activity and controllable Cu-ZnO interactions derived from copper silicate nanotubes. A series of Cu-ZnO/SiO2 samples with different amounts of ZnO were prepared. The activities of the as-prepared catalysts for methanol synthesis were tested, and the results revealed a volcano relationship with the weight fraction of ZnO. At 523 K, the methanol selectivity increased from 20% to 67% when 14% ZnO was added to the Cu/SiO2 catalyst, while the conversion of CO2 increased first and then decreased with the addition of ZnO. The optimum space time yield (STY) of 244 g·kg-1·h-1 was obtained on C-SiO2-7%ZnO at 543 K under 4.5 MPa H2/CO2. Furthermore, the synergistic effect of Cu and ZnO was studied by high resolution transmission electron microscopy (HRTEM), powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), in situ diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS), and temperature-programmed reduction (TPR) analyses. The HRTEM images showed that the Cu particles come in contact with ZnO more frequently with increased addition of ZnO, indicating that the catalysts with higher ZnO contents have a greater probability of formation of the Cu-ZnO interface, which promotes the catalytical activity of Cu-ZnO/SiO2. Meanwhile, the HRTEM images, XRD patterns, and TPR results showed that the addition of excess ZnO leads to an increase in the size of the Cu particles, which in turn decreases the total number of active sites and further degrades the activity of the catalysts. The activation energy (Ea) for methanol synthesis and reverse water gas shift (RWGS) was calculated based on the results of the catalytical test. With the addition of ZnO, Ea for methanol synthesis decreased from 72.5 to 34.8 kJ·mol-1, while that for RWGS increased from 61.3 to 102.7 kJ·mol-1, illustrating that ZnO promotes the synergistic effect of Cu-ZnO. The results of XPS and in situ DRIFTS showed that the amount of Cu+ species decreases with the addition of ZnO, indicating that the Cu-ZnO interface serves as the active site. The Cu surface area and the turnover frequency (TOF) of methanol were calculated based on the H2-TPR curves. The TOF of methanol on the Cu-ZnO/SiO2 catalysts at 543 K increased from 1.5 × 10-3 to 3.9 × 10-3 s-1 with the addition of ZnO, which further confirmed the promotion effect of the Cu-ZnO interface on the methanol synthesis. This study provides a method to construct Cu-ZnO interfaces based on copper silicate and to investigate the influence of ZnO on Cu-ZnO/SiO2 catalysts. 相似文献
500.
Dongni Liu Prof. Dongyun Chen Prof. Najun Li Prof. Qingfeng Xu Prof. Hua Li Prof. Jinghui He Prof. Jianmei Lu 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(11):4549-4554
BiOBr containing surface oxygen vacancies (OVs) was prepared by a simple solvothermal method and combined with graphitic carbon nitride (g-C3N4) to construct a heterojunction for photocatalytic oxidation of nitric oxide (NO) and reduction of carbon dioxide (CO2). The formation of the heterojunction enhanced the transfer and separation efficiency of photogenerated carriers. Furthermore, the surface OVs sufficiently exposed catalytically active sites, and enabled capture of photoexcited electrons at the surface of the catalyst. Internal recombination of photogenerated charges was also limited, which contributed to generation of more active oxygen for NO oxidation. Heterojunction and OVs worked together to form a spatial conductive network framework, which achieved 63 % NO removal, 96 % selectivity for carbonaceous products (that is, CO and CH4). The stability of the catalyst was confirmed by cycling experiments and X-ray diffraction and transmission electron microscopy after NO removal. 相似文献