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负载型金纳米颗粒催化剂在许多催化反应中展现出非常好的催化活性,但是金纳米颗粒在高温等反应条件下容易烧结团聚,极大地限制了金催化剂的应用。利用原子层沉积技术在Au/TiO2催化剂表面分别精确沉积了一层超薄的二氧化钛和氧化铝包裹层,并对比研究了包裹层对金纳米颗粒的热稳定性影响。原位红外漫反射CO吸附和x-射线光电子能谱数据证实了氧化物包裹层的存在。发现亚纳米厚的氧化铝包裹层能够在600 C完全避免金纳米颗粒的团聚;相反,二氧化钛包裹层对金纳米颗粒稳定性的提高没有明显效果。通过CO氧化探针反应的活性测试,发现随着煅烧温度的升高氧化铝包裹的Au/TiO2 催化剂的活性逐渐提高,表明高温处理可以促进被包裹金原子的暴露并表现出催化活性。提供了提高金纳米颗粒稳定性的有效方法,为拓展金催化剂在条件苛刻的反应中的应用奠定了技术基础. 相似文献
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采用初湿浸渍和溶胶凝胶法分别制备了Li/MgO催化剂和Li/MgO纳米催化剂. 比较两种Li/MgO催化剂对于甲烷氧化偶联反应的催化性能. 采用X射线衍射、BET吸附和透射电镜进行了表征.在973-1073 K和总压力为101 kPa下对催化剂进行了测试. 实验结果表明,Li/MgO纳米催化剂比普通催化剂对于甲烷氧化偶联反应表现为更高的甲烷转换率,较高选择性和较高的的主要产品(乙烷和乙烯)的产率. 相似文献
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《中国光学与应用光学文摘》2006,(5)
O644.12006054769纳米Ce1-xZrxO2催化剂上乙醇催化氧化发光研究=Cata-lytic oxidation cataluminescence of ethanol over catalystsCe1-xZrxO2[刊,中]/叶青(清华大学化学系,有机光电子与分子工程教育部重点实验室.北京(100084)),张新荣…//高等学校化学学报.—2006,27(4).—726-730研究了纳米Ce1-xZrxO2上乙醇催化氧化发光特性,重点考察了反应温度和催化剂组成[n(Ce)/n(Zr)]对发光强度的影响。在相近的反应条件下研究了纳米Ce1-xZrxO2上乙醇催化氧化反应的活性、选择性和可能的催化发光机理。结果表明,催化发光强度与催化反应中生成… 相似文献
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在pH 2.27的柠檬酸钠-盐酸缓冲溶液中,纳米金对氯金酸-盐酸羟胺生成较大粒径金颗粒这一慢反应具有较强的催化作用。较大粒径金颗粒在600~1 000 nm处有一个较宽的吸收峰。将纳米金标记羊抗人IgG获得免疫纳米金,免疫纳米金也具有相同催化效果。在一定条件下,金标记羊抗人IgG与IgG发生特异性结合生成纳米金免疫复合物。以16 000 rpm速度离心分离获得未反应的纳米金标抗上层溶液。以它作为催化剂催化氯金酸-盐酸羟胺微粒反应,700 nm处的吸光度A700 nm线性降低。其降低值ΔA700 nm与IgG在0.1~10 ng·mL-1范围内呈良好线性关系, 检出限为0.06 ng·mL-1。本法具有灵敏、快速和较高的特异性,用于定量分析人血清IgG,结果满意。 相似文献
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通过在三维还原氧化石墨烯孔径中原位生长ZIF-8纳米粒子,制备了三维金属有机骨架/石墨烯催化剂.这种ZIF-8/rGO纳米复合材料同时具有介孔和微孔,并且拥有高比表面积和大量催化位点,是生物质转化的理想催化剂.将纤维素溶解于氢氧化钠水溶液中,在水热条件下,使用这种催化剂,纤维素可以被充分降解转化.纤维素转化率可以达到100%,其主要产物是甲酸,产率最高可达93.66%.催化剂还可以被回收,重复使用依然具有很好的催化效果. 相似文献
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《化学物理学报》2018,(4)
电催化水分解的速率控制步骤是水的氧化反应.高活性的电催化剂可加速水氧化的反应速率从而提升水分解反应的整体效果.我们通过水热-热解法制备了一种高活性的Co304催化剂去高效电催化产氧气.电镜表征证实了Co3O4具有超薄的纳米片层结构,X射线光电子能谱及电子顺磁共振波谱确认了Co304纳米片中存在大量氧空位.大幅提高的比表面积有利于更多包括作为活性点位的氧缺陷在内的点位暴露.Co304纳米片可加速阳极与电解质之间的产氧气反应,以很低的过电势(310 mV)及电流密度(10 mA/cm~2)高效催化产氧气,在1.0 mol/L KOH中表现出突出的稳定性. 相似文献
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Advanced oxidation processes can potentially eliminate organic contaminants from industrial waste streams as well as persistent pharmaceutical components in drinking water. We explore for the first time the utilization of Cavitation Intensifying Bags (CIB) in combination with Pd/Al2O3 catalyst as possible advanced oxidation technology for wastewater streams, oxidizing terephthalic acid (TA) to 2-hydroxyterephthalic acid (HTA). The detailed characterization of this novel reaction system reveals that, during sonication, the presence of surface pits of the CIB improves the reproducibility and thus the control of the sonication process, when compared to oxidation in non-pitted bags. Detailed reaction kinetics shows that in the CIB reactor the reaction order to TA is zero, which is attributed to the large excess of TA in the system. The rate of HTA formation increased ten-fold from ~0.01 μM*min−1 during sonication in the CIB, to ~0.10 μM*min−1 for CIB in the presence of the Pd/Al2O3 catalyst. This enhancement was ascribed to a combination of improved mass transport, the creation of thermal gradients, and Pd/Al2O3 catalyst near the cavitating bubbles. Further analysis of the kinetics of HTA formation on Pd/Al2O3 indicated that initially the reaction underwent through an induction period of 20 min, where the HTA concentration was ~0.3 μM. After this, the reaction rate increased reaching HTA concentrations ~6 μM after 40 min. This behavior resembled that observed during oxidation of hydrocarbons on metal catalysts, where the slow rate formation of hydroperoxides on the metal surface is followed by rapid product formation upon reaching a critical concentration. Finally, a global analysis using the Intensification Factor (IF) reveals that CIB in combination with the Pd/Al2O3 catalyst is a desirable option for the oxidation of TA when considering increased oxidation rates and costs. 相似文献
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Y. Badr 《Journal of Physics and Chemistry of Solids》2007,68(3):413-419
The silica nanoparticles (SiO2 NPs), silver (Ag) NPs and gold (Au) NPs coated with SiO2 NPs (core-shell) were prepared. The sizes and morphology of the particles were indicated. The three prepared NPs were used for photocatalytic degradation of methyl orange (MO) dye by xenon lamp. Rate of photocatalytic degradation reaction constant and lifetime were calculated for each catalyst. Moreover, the mechanism of the photocatalytic reaction was studied. 相似文献
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Comparing the Contribution of Visible‐Light Irradiation,Gold Nanoparticles,and Titania Supports in Photocatalytic Nitroaromatic Coupling and Aromatic Alcohol Oxidation 下载免费PDF全文
Jian Zhao Xuebin Ke Hongwei Liu Yiming Huang Chao Chen Arixin Bo Xianliang Sheng Huaiyong Zhu 《Particle & Particle Systems Characterization》2016,33(9):628-634
Under visible‐light irradiation, gold nanoparticles (Au NPs) supported by titania (TiO2) nanofibers show excellent activity and high selectivity for both reductive coupling of nitroaromatics to corresponding azobenzene or azoxylbenzene and selective oxidation of aromatic alcohols to corresponding aldehydes. The Au NPs act as active centers mainly due to their localized surface plasmon resonance (LSPR) effect. They can effectively couple the photonic energy and thermal energy to enhance reaction efficiency. Visible‐light irradiation has more influence on the reduction than on the oxidation, lowering the activation energy by 24.7 kJ mol?1 and increasing the conversion rate by 88% for the reductive coupling, compared to merely 8.7 kJ mol?1 and 46% for the oxidation. Furthermore, it is found that the conversion of nitroaromatics significantly depends on the particle size and specific surface area of supported Au NPs; and the catalyst on TiO2(B) support outperforms that on anatase phase with preferable ability to activate oxygen. In contrast, for the selective oxidation, the effect of surface area is less prominent and Au NPs on anatase exhibit higher photo‐catalytic activity than other TiO2 phases. The catalysts can be recovered efficiently because the Au NPs stably attach to TiO2 supports by forming a well‐matched coherent interface observed via high‐resolution TEM. 相似文献
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Phyllanthin-assisted biosynthesis of silver and gold nanoparticles: a novel biological approach 总被引:2,自引:0,他引:2
Abstract The anisotropic gold and spherical–quasi-spherical silver nanoparticles (NPs) were synthesized by reducing aqueous chloroauric
acid (HAuCl4) and silver nitrate (AgNO3) solution with the extract of phyllanthin at room temperature. The rate of reduction of HAuCl4 is greater than the AgNO3 at constant amount of phyllanthin extract. The size and shape of the NPs can be controlled by varying the concentration of
phyllanthin extract and thereby to tune their optical properties in the near-infrared region of the electromagnetic spectrum.
The case of low concentration of extract with HAuCl4 offers slow reduction rate along with the aid of electron-donating group containing extract leads to formation of hexagonal-
or triangular-shaped gold NPs. Transmission electron microscopy (TEM) analysis revealed that the shape changes on the gold
NPs from hexagonal to spherical particles with increasing initial concentration of phyllanthin extract. The Fourier transform
infrared spectroscopy and thermogravimetric analyses reveal that the interaction between NPs and phyllanthin extract. The
cyclic voltammograms of silver and gold NPs confirms the conversion of higher oxidation state to zero oxidation state.
Graphical abstract Anisotropic gold and silver nanoparticles were synthesized by a simple procedure using phyllanthin extract as reducing agent.
The rate of bioreduction of AgNO3 is lower than the HAuCl4 at constant concentration of phyllanthin extract. The required size of the nanoparticles can be prepared by varying the concentration
of phyllanthin with AgNO3 and HAuCl4.
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Two-dimensional (2D) hexagonally close-packed arrays of water-dispersed gold nanoparticles (NPs) on highly hydrophilic sputter-deposited SiO2 surfaces were fabricated via an evaporation-induced self-assembly process. Using a non-ionic amphiphilic glycol derivative with the thiol head group, 1-mercapto-3,6,9-trioxodecane, as a stabilization ligand, high-concentration Au NPs were stably dispersed in water, and self-assembled into μm-sized well-ordered 2D arrays on SiO2 surfaces during the solvent evaporation on SiO2 surfaces. Due to the non-ionic character of the ligand, the particle–particle interactions may only depend on the capillary and van der Waals forces, and not on the electric double-layer forces that change with ion/electrolyte concentrations during the solvent evaporation. This study provides an approach to fabrication of close-packed 2D arrays of water-dispersed NPs instead of using toxicological organic solvent or complex water-organic phase transfer process. Meanwhile, this approach will make it easier to study their self-assembly mechanisms in a variety of solvents by simplifying ambiguous particle–particle interactions. 相似文献
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Several bimetallic NiAg catalysts for the lignin hydrogenolysis reaction are evaluated. NiAg catalysts are either prepared by wet chemical reduction, in which a mixture of AgNO3 and Ni(NO3)2 or a mixture of AgOAc and Ni(OAc)2 is reduced by NaBH4 and stabilized by polyvinylpyrrolidone in water, or by the decomposition–precipitation method to obtain NiAg/SiO2. These three catalysts exhibit distinct performances in hydrogenolysis of a lignin β‐O‐4 model compound. For colloidal catalyst from co‐reduction of AgOAc and Ni(OAc)2, separate growths of Ag and Ni nanoparticles (NPs) are observed, and the system exhibits an undesired selectivity of 31.5% toward dimer products. On the other hand, NiAg NPs are dominant after the reduction of nitrate precursors, although the NP size is not sufficiently small (6.7 nm), resulting in high selectivity but a low reaction rate (12.6% conversion with 12.1% monomers yield). Bimetallic NiAg active phase with excellent dispersion (≈1.5 nm) is obtained on NiAg/SiO2, which enables 72.7% substrate conversion and 65.6% yield of target monomer compounds. From these results, NiAg bimetallic catalyst is indeed superior to monometallic Ni in lignin hydrogenolysis, however, the formation of bimetallic NiAg catalyst is highly sensitive to the preparation conditions—proper selection of precursors, reductant, and support/stabilizer are all crucial. 相似文献
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Two-dimensional (2D) hexagonally close-packed arrays of water-dispersed gold nanoparticles (NPs) on highly hydrophilic sputter-deposited SiO2 surfaces were fabricated via an evaporation-induced self-assembly process. Using a non-ionic amphiphilic glycol derivative with the thiol head group, 1-mercapto-3,6,9-trioxodecane, as a stabilization ligand, high-concentration Au NPs were stably dispersed in water, and self-assembled into μm-sized well-ordered 2D arrays on SiO2 surfaces during the solvent evaporation on SiO2 surfaces. Due to the non-ionic character of the ligand, the particle–particle interactions may only depend on the capillary and van der Waals forces, and not on the electric double-layer forces that change with ion/electrolyte concentrations during the solvent evaporation. This study provides an approach to fabrication of close-packed 2D arrays of water-dispersed NPs instead of using toxicological organic solvent or complex water-organic phase transfer process. Meanwhile, this approach will make it easier to study their self-assembly mechanisms in a variety of solvents by simplifying ambiguous particle–particle interactions.This revised version was published online in August 2005 with a corrected issue number. 相似文献
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Pulsed laser ablation of Aluminium (Al) in pure water rapidly forms a thin alumina (Al2O3) layer which drastically modifies surface plasmon resonance (SPR) absorption characteristics in deep-UV region. Initially, pure aluminium nanoparticles (NPs) are generated in water without any stabilizers or surfactants at low laser fluence which gradually transform to stable Al-Al2O3 core-shell nanostructure with increasing either residency time or fluence. The role of laser wavelength and fluence on the SPR properties and oxidation characteristics of Al NPs has been investigated in detail. We also present a one-step in situ synthesis of oxide-free stable Al NPs in biocompatible polymer solutions using laser ablation in liquid method. We have used nonionic polymers (PVP, PVA and PEG) and anionic surfactant (SDS) stabilizer to suppress the Al2O3 formation and studied the effect of polymer functional group, polymeric chain length, polymer concentration and anionic surfactant on the incipient embryonic aluminium particles and their sizes. The different functional groups of polymers resulted in different oxidation states of Al. PVP and PVA polymers resulted in pure Al NPs; however, PEG and SDS resulted in alumina-modified Al NPs. The Al nanoparticles capped with PVP, PVA, and PEG show a good correlation between nanoparticle stability and monomeric length of the polymer chain. 相似文献
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Juan Carlos F. Rodríguez-Reyes Cynthia M. Friend Robert J. Madix 《Surface science》2012,606(15-16):1129-1134
Benzyl alcohol has received substantial attention as a probe molecule to test the selectivity and efficiency of novel metallic gold catalysts. Herein, the mechanisms of benzyl alcohol oxidation on a gold surface covered with atomic oxygen are elucidated; the results show direct correspondence to the reaction on gold-based catalysts. The selective, partial oxidation of benzyl alcohol to benzaldehyde is achieved with low oxygen surface concentrations and takes place through dehydrogenation of the alcohol to form benzaldehyde via a benzyloxy (C6H5–CH2O) intermediate. While in this case atomic oxygen plays solely a dehydrogenating role, at higher concentrations it leads to the formation of intermediates from benzaldehyde, producing benzoic acid and CO2. Facile ester (benzyl benzoate) formation also occurs at low oxygen concentrations, which indicates that benzoic acid is not a precursor of further oxidation of the ester; instead, the ester is produced by the coupling of adsorbed benzyloxy and benzaldehyde. Key to the high selectivity seen at low oxygen concentrations is the fact that the production of the aldehyde (and esters) is kinetically favored over the production of benzoic acid. 相似文献
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Yingju Yang Jing Liu Zhen Wang Yingni Yu 《Proceedings of the Combustion Institute》2021,38(3):4317-4325
Experiments and density functional theory calculations were conducted to uncover the reaction chemistry of Hg0 oxidation during SO2/SO3 conversion over V2O5/TiO2 catalyst. The results show that SO2 promotes Hg0 oxidation over V2O5/TiO2 catalyst with the assistance of oxygen. The promotional effect is dependent on the reaction temperature, and is associated with the bimolecular reaction between Hg0 and SO3 over V2O5/TiO2 catalyst. SO2 can be oxidized to SO3 which has high oxidation ability for Hg0 oxidation. SO2/SO3 conversion proceeds through a three-step reaction process in the sequence of SO2 adsorption → SO2 oxidation → SO3 desorption. SO2 oxidation presents an activation energy barrier of 223.84 kJ/mol. HgSO4 species is formed from the bimolecular reaction between Hg0 and SO3 over V2O5/TiO2 catalyst. Hg0 oxidation by SO3 over V2O5/TiO2 catalyst occurs through three reaction pathways, which are energetically favorable for HgSO4 formation. SO2* → SO3* is identified as the rate-determining step of HgSO4 formation. During Hg0 oxidation by SO3 over V2O5/TiO2 catalyst, HgSO4 desorption is a highly endothermic reaction process and requires a higher external energy. The proposed skeletal reaction network can be used to well understand the reaction mechanism of Hg0 oxidation during SO2/SO3 conversion over V2O5/TiO2 catalyst. 相似文献