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11.
Selective hydrogenation of benzene to cyclohexene on Ru-basecatalysts promoted with Mn and Zn 下载免费PDF全文
Ru-based catalysts promoted with Mn and Zn were prepared by a co-precipitation method. In liquid-phase hydrogenation of benzene, the Ru-Mn-Zn catalysts exhibited superior catalytic performance to the catalysts promoted with Zn or Mn alone. The optimum Mn/Zn molar ratio was determined to be 0.3. With the addition of 0.5 g NaOH, the Ru-Mn-Zn-0.3 catalyst, which was reduced at 150 ? C, afforded a cyclohexene selectivity of 81.1% at a benzene conversion of 60.2% at 5 min and a maximum cyclohexene yield of 59.9% at 20 min. Based on characterizations, the excellent performance of Ru-Mn-Zn catalyst was ascribed to the suitable pore structure, the appropriate reducibility and the homogenous chemical environment of the catalyst. 相似文献
12.
Xiaoli Wu Xulin Cui Wenjia Wu Jingtao Wang Yifan Li Zhongyi Jiang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(51):18695-18700
Lamellar membranes with well‐defined 2D nanochannels show fast, selective permeation, but the underlying molecular transport mechanism is unexplored. Now, regular robust MXene Ti3C2Tx lamellar membranes are prepared, and the size and wettability of nanochannels are manipulated by chemically grafted hydrophilic (?NH2) or hydrophobic (?C6H5, ?C12H25) groups. These nanochannels have a sharp difference in mass transfer behavior. Hydrophilic nanochannels, in which polar molecules form orderly aligned aggregates along channel walls, impart ultrahigh permeance (>3000 L m?2 h?1 bar?1), which is more than three times higher than that in hydrophobic nanochannels with disordered molecular configuration. In contrast, nonpolar molecules with disordered configuration in both hydrophilic and hydrophobic nanochannels have comparable permeance. Two phenomenological transport models correlate the permeance with the mass transport mechanism of molecules that display ordered and disordered configuration. 相似文献
13.
Ming Zhu Guanyao Wang Xing Liu Bingkun Guo Gang Xu Zhongyi Huang Minghong Wu Hua‐Kun Liu Shi‐Xue Dou Chao Wu 《Angewandte Chemie (International ed. in English)》2020,59(16):6596-6600
Sodium metal is an ideal anode material for metal rechargeable batteries, owing to its high theoretical capacity (1166 mAh g?1), low cost, and earth‐abundance. However, the dendritic growth upon Na plating, stemming from unstable solid electrolyte interphase (SEI) film, is a major and most notable problem. Here, a sodium benzenedithiolate (PhS2Na2)‐rich protection layer is synthesized in situ on sodium by a facile method that effectively prevents dendrite growth in the carbonate electrolyte, leading to stabilized sodium metal electrodeposition for 400 cycles (800 h) of repeated plating/stripping at a current density of 1 mA cm?2. The organic salt, PhS2Na2, is found to be a critical component in the protection layer. This finding opens up a new and promising avenue, based on organic sodium slats, to stabilize sodium metals with a protection layer. 相似文献
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Yi Yang Xueyi He Penghui Zhang Yassin H. Andaloussi Hailu Zhang Zhongyi Jiang Yao Chen Shengqian Ma Peng Cheng Zhenjie Zhang 《Angewandte Chemie (International ed. in English)》2020,59(9):3678-3684
Developing new materials for the fabrication of proton exchange membranes (PEMs) for fuel cells is of great significance. Herein, a series of highly crystalline, porous, and stable new covalent organic frameworks (COFs) have been developed by a stepwise synthesis strategy. The synthesized COFs exhibit high hydrophilicity and excellent stability in strong acid or base (e.g., 12 m NaOH or HCl) and boiling water. These features make them ideal platforms for proton conduction applications. Upon loading with H3PO4, the COFs (H3PO4@COFs) realize an ultrahigh proton conductivity of 1.13×10?1 S cm?1, the highest among all COF materials, and maintain high proton conductivity across a wide relative humidity (40–100 %) and temperature range (20–80 °C). Furthermore, membrane electrode assemblies were fabricated using H3PO4@COFs as the solid electrolyte membrane for proton exchange resulting in a maximum power density of 81 mW cm?2 and a maximum current density of 456 mA cm?2, which exceeds all previously reported COF materials. 相似文献
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<正>We present a novel method for realizing double-image encryption algorithm by combining the images in different transform domains.Two original images are encrypted into two interim images by fractional Fourier transform and gyrator transform,respectively.The two encrypted images can be obtained by means of the addition and subtraction of the two interim images.This is defined as a double-image sharing scheme,in which the original images are encrypted into two parts.The original images cannot be recovered only with any one of the two interim images.Numerical simulation experiments demonstrate the validity of the algorithm. 相似文献
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CO2的有效利用有助于解决环境和生态问题.碳酸酐酶(CA)等酶分子可精准活化CO2分子以降低反应能垒,为CO2的高效和高选择性转化提供了一种有前景的途径.然而,酶离开生物体后易失活,且难以重复利用.目前,包埋型固定化酶是常用且有效的提高酶稳定性与回用率的方法之一,但载体的存在会造成反应物CO2内扩散阻力增加,降低反应活性.此外,CO2酶促转化是一个气-液-固三相反应过程,反应体系中CO2的外扩散性能也需要加强.金属有机骨架(MOFs),特别是咪唑酯骨架(ZIFs),常被用作酶固定化的载体.ZIFs的拓扑结构可被设计成不同形貌,进而通过ZIFs的结构工程来加强分子向其中的内扩散.Pickering乳液是指以固体颗粒代替常规表面活性剂而稳定的乳液.当固体颗粒具有催化活性时,催化剂颗粒会扩大液-液-固或气-液-固三相接触面积,从而有效协调反应物在不同相中的扩散时间.如果酶被用作这些颗粒的活性中心,所制备的Pickering乳液也可能具备类似的特性,可加强底物分子向酶的外扩散.本文选择两种具有不同结构的ZIFs(ZIF-L和ZIF-8),原位包埋CA后形成CA@ZIFs颗粒以稳定Pickeirng乳液.ZIF-L和CA@ZIF-L颗粒显示出独特的二维层状堆叠结构.ZIF-8和CA@ZIF-8颗粒呈棱角清晰的十二面体结构.与CA@ZIF-8颗粒相比,CA@ZIF-L颗粒显示出更大的孔径和更宽的孔径分布,这有助于CO2从CA@ZIF-L颗粒表面扩散至酶活性中心.利用酶活测试来研究内扩散是否通过结构工程得到了加强,发现CA@ZIF-L颗粒的活性比CA@ZIF-8颗粒高22.3%,推测这是由于CA@ZIF-L颗粒特殊的十字花状结构会缩短CO2从颗粒表面扩散至酶活性中心的距离.同时,十字花状结构可暴露更多的酶活性位点(CA@ZIF-L颗粒的暴露面积是CA@ZIF-8颗粒的~8倍),从而提升了反应物浓度并显示出更高的催化活性.本文还设计了吸附实验来进一步验证上述假设,发现BSA@ZIF-L颗粒对香豆素的吸附率远高于BSA@ZIF-8颗粒,说明与ZIF-8相比,酶包埋于ZIF-L具有更强的捕获小分子的能力,表明CO2分子向CA@ZIF-L的扩散速度更快,即CA@ZIF-L的十字花状结构可强化系统的内扩散过程.进一步比较了PIBS和游离多酶体系的催化活性,将CO2通入每个系统,在反应前20 min,PIBS的pH值下降速度比游离体系快得多,说明PIBS通过在气相和液相间构建更大的界面,缩短了CO2向CA的扩散距离,从而提高了催化效率,促进了CO2转化.上述假设也通过扩散动力学的计算得到了验证.为进一步研究PIBS的CO2矿化能力,本文开展了CaCO3矿化反应,发现PIBS的CaCO3产量远高于游离多酶体系,表明构建的PIBS在强化内外扩散方面具有显著优势.最后,评估了PIBS在工业应用中的性能,由CA@ZIF-L和CA@ZIF-8颗粒构建的PIBS显示出较好的可回收性,在第8个循环后,PIBS仍可保持8.9 mg/5 min的CaCO3产量.综上,PIBS可为CO2的酶促转化和框架提供一个新方法和新平台. 相似文献
18.
采用共沉淀法制备了一系列不同Mn含量的纳米Ru-Mn催化剂,考察了纳米ZrO2作分散剂时它们催化苯选择加氢制环己烯的反应性能,并采用X射线衍射、透射电镜、N2物理吸附、X射线荧光、原子吸收光谱和俄歇电子能谱等手段对催化剂进行了表征.结果表明,Ru-Mn催化剂上Mn以Mn3O4存在于Ru的表面上.在加氢过程中,Mn3O4可以与浆液中ZnSO4发生化学反应生成一种难溶性的(Zn(OH)2)3(ZnSO4)(H2O)3盐.该盐易化学吸附在Ru催化剂表面上,从而在提高Ru催化剂上环己烯选择性起关键作用.当催化剂中Mn含量为5.4%时,环己烯收率为61.3%,同时具有良好的稳定性和重复使用性能. 相似文献
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Zhongyi Guo Jinmei Feng Keya Zhou Yanjun Xiao Shiliang Qu Jung-Ho Lee 《Applied Physics A: Materials Science & Processing》2012,108(3):639-644
The interactions between femtosecond (fs) laser pulses and a thin Au film deposited on a silica glass substrate were systematically investigated based on experimental data. Different structures, including microholes, nanoholes, and nanobumps, are obtained when pulses with different energies are incident on the surface of a gold film. The experimental results are discussed according to specific experimental parameters. Two physical models were constructed in order to explain the experimental results. The formation of nanoholes in a silica substrate is attributed to etching by higher order harmonic generations (HHG) when the femtosecond laser pulse interacts with the generated plasma layer, while the formation of nanobumps on the surface of an Au film is attributed to the elastic and plastic characteristics of the metal film under laser pulse irradiation. 相似文献