溶胶-凝胶法制备负载型纳米催化剂

本文介绍了过渡金属醇盐（TMA）溶胶-凝胶化学的基本知识，着重讨论了用溶胶-凝胶法制备纳米催化剂过程中的影响因素，并指出研究的重要意义和前景。     

活性炭负载金属催化剂的研究进展

活性炭作为一种优良的催化剂载体被广泛应用于催化领域,其经酸碱预处理或氧化预处理后表面可负载一种或多种金属催化剂,是优化各种金属催化剂性能的有效方法之一。为给今后活性炭载体催化剂的研发提供一些参考和方向,从单一金属催化剂负载和复合金属催化剂负载的制备、催化活性及应用着手,对近年来新制备的活性炭负载金属催化剂进行综述。     

金属氧化物纳米颗粒溶胶-凝胶合成概述

文章介绍了金属氧化物纳米颗粒的水溶胶-凝胶合成与非水溶胶-凝胶合成的一般工艺过程和影响合成工艺的主要因素,总结了常见合成反应的类型与简单反应机理.并对作水合成中的表面活性剂控制与溶剂控制两种方法的优缺点进行了比较.     

溶胶-凝胶法制备纳米尺度催化剂的研究进展

介绍了溶胶-凝胶法制备纳米尺度催化剂的基本过程和其最新研究进展。指出:将溶胶-凝胶法与其他技术相结合,从而提高纳米催化剂的稳定性,将是溶胶-凝胶法在纳米催化剂制备中的发展方向。     

溶胶-凝胶法制备Li_2ZrO_3纳米颗粒及其高温二氧化碳吸收性能

通过柠檬酸溶胶-凝胶法制备纳米级锆酸锂(Li_2ZrO_3)材料,利用扫描电子显微镜和X射线衍射仪对Li_2ZrO_3材料的形貌与结构进行表征,利用热重分析仪测试Li_2ZrO_3材料的高温CO_2吸收性能.结果表明,合成的Li_2ZrO_3材料具有良好的高温CO_2吸收性能.在CO_2分压为0.05 MPa、550℃、20min内吸收容量可达20%(质量分数);45 min内可达吸收平衡,平衡吸收量达27%(质量分数).经3次吸收解吸循环后其吸收性能没有明显下降,表明Li_2ZrO_3材料具有良好的稳定性.     

活性炭负载TiO2的制备及其光催化活性研究

采用溶胶-凝胶法制备TiO2/活性炭(AC)光催化剂,采用XRD分析了纳米TiO2晶型,SEM观察了活性炭负载前后表面形貌.正交试验分析了各因素对光催化降解甲基橙的影响.结果表明:制备的纳米TiO2为纯锐钛矿型,催化剂以不规则碎片包覆在活性炭表面.复合材料在TiO2浓度0.441 mol/L,50℃烘干后,pH=3的环境下降解甲基橙,脱色率达到95.5％.溶液pH值是催化降解的主要影响因素.     

溶胶-凝胶法制备纳米二氧化硅

本文通过溶胶一凝胶法制备纳米SiO2。考察了不同温度、pH值、催化剂对制备纳米SiO2的影响。并运用了TEN表征了纳米SiO2的粒径大小、分散度以及粒子性状，得出了制备纳米SiO2较好的工艺条件。     

溶胶-凝胶法负载型催化剂上糠醛加氢制备2-甲基呋喃

采用溶胶-凝胶法制备负载型Cu-Cr/SiO2催化剂,进行糠醛气相加氢合成2-甲基呋喃。在无梯度反应器中考察了Cu/Cr摩尔比、温度、氢醛摩尔比对催化加氢性能的影响。并通过X射线衍射探讨了催化剂的活性中心成分。     

溶胶-乳化-凝胶法合成纳米TiO2颗粒尺寸影响因素研究

以钛酸丁酯为原料,通过溶胶-乳化-凝胶法合成了纳米TiO2粉末。探讨了表面活性剂浓度、溶胶的pH值、水含量对粒径的大小和粒度分布的影响。用XTEM对纳米二氧化钛粉体的形貌进行了分析。研究表明:当表面活性剂达到临界胶束浓度时颗粒尺寸较小且分布较均匀,当溶胶的pH值为8～9,水溶液浓度为0.5 mol/L时颗粒尺寸基本保持不变。在氮气气氛下,400℃煅烧可达到最好的实用效果。     

等离子体制备负载型金属纳米催化剂的研究进展

等离子体主要是由离子、电子等粒子组成的呈电中性且高度离子化的气体。可在室温条件下,利用等离子体中的高能粒子对化学物质进行还原,避免高温条件下粒子发生团聚,易得到粒径小、分散性好的纳米颗粒。对近年来等离子体技术制备负载型金属纳米催化剂及其催化性能进行了综述。     

Optimization of particle size,dispersity, and conductivity of 8 mol% Y2O3 doped tetragonal zirconia polycrystalline nanopowder prepared by modified sol-gel method via activated carbon absorption

8 mol% Y₂O₃ doped tetragonal zirconia polycrystalline (8Y-TZP) ceramic nanopowders were synthesized via a novel modified sol-gel method employing zirconium carbonate basic as zirconium resources. The activated carbon as a dispersant was added to the precursor solution during the formation of the sol. The phase behavior, thermal decomposition, microstructure morphology, and electrochemical performance of nanopowders with the addition of activated carbons were investigated by X-ray diffraction (XRD), differential thermal analysis (DTA), scanning electron microscopy (SEM), particles size distribution, and electrochemical impedance spectroscopy analysis (EIS). After adding the activated carbon, the average crystallite size of 8Y-TZP nanopowders decreased from about 53.16–33.51 nm when calcined at 900 ℃, and the 8Y-TZP nanopowders were produced loosely agglomerated. Meanwhile, compacts prepared by pressing the as-obtained 8Y-TZP nanopowders sintered to 98.8% relative density at 1600 ℃ and exhibited an average grain size of 0.89 µm, which brought a positive effect on ionic conductivity (0.079 S·cm^?1).     

溶胶-自蔓延法制备La0.8Sr0.2Mn0.8Ni0.2O3催化剂的优化条件

采用溶胶-凝胶-自蔓延法合成较大比表面积的钙钛矿型复合氧化物La_0.8Sr_0.2Mn_0.8Ni_0.2O₃催化剂,研究了pH、苹果酸用量和焙烧温度对催化剂的影响,通过XRD、BET和SEM等分析手段对催化剂进行了表征。结果表明,pH=3、苹果酸用量为金属离子总物质的量2倍和焙烧温度600 ℃为最佳制备工艺条件。催化剂在低温对CO催化燃烧显示出良好的催化活性。     

Effect of heat treatment of activated carbon supports on the loading and activity of Pt catalyst

The study has been done on the effect of heat treatment of activated carbon at 1573-1773 K on its structural and electronic properties as a catalyst support. The X-ray diffraction result indicated that a partly graphitized structure was formed when the activated carbon was heated to a high temperature (1673 K). From the X-ray photoelectron spectroscopy result, it was found that Pt⁰ concentration was increased, but PtO and PtO₂ concentrations were decreased with an increase in the heat treatment temperature. From the van Dam’s model applied to this result, it might be concluded that more “π-sites” are created as the heat treatment temperature becomes higher. From the CO-chemisorption result, the highest loading was observed in case of Pt/AC1673 sample. This improved loading ability could be explained by the special interaction of the graphitic planes (π-sites) with the metal particles. Based on the catalytic activity, CO-chemisorption and XPS results, it is concluded that the well-loaded Pt⁰ species mainly contribute to the catalytic activity. Moreover, it was found that different degrees of graphitization of heat treated activated carbon could cause different surface Pt⁰ and improve the resistance of carbon support against gasification under air oxidation.     

Fabrication of metal nanoparticles on highly dispersed pristine carbon nanotubes

A convenient approach to fabricate metal (i.e. gold, platinum, and palladium) nanoparticles on highly dispersed pristine carbon nanotubes (CNTs) was developed using a conjugated block copolymer of poly(3-hexylthiophene)-b-poly(vinylpyrrolidone) (P3HT-b-PVP). P3HT-b-PVP not only provides a stable dispersion of pristine CNTs through the π–π interactions between P3HT block and CNTs, but also introduces PVP groups on CNT surfaces to induce the heterogeneous nucleation of metal nanoparticles and protect them from aggregating. The density of metal nanoparticles on CNT surfaces was controlled by the metal salt/CNT feed ratio. The simple processing procedure, versatility in synthesizing various metal nanoparticles, high metal nanoparticle loading capacity, and excellent dispersibility and processability of the product make this approach a promising method to fabricate metal nanoparticles on CNTs.     

The loss rate by sublimation of mercuric chloride adsorbed on activated carbon

This paper reports on the directly measured loss rate by sublimation of mercuric chloride supported on the surface of activated carbon in the process of synthesizing vinyl chloride. An equation is derived for the sublimation rate. The result coincides with the practice in production and the data in literature. The desorption heat was calculated from the desorption equilibrium data by means of the Clausius—Clapeyron equation. It was found that the desorption heat is related to the degree of coverage of mercuric chloride and the average heat value is identical with the evaporation heat. This research provides some fundamental data for research into catalyst deactivation caused by the loss of active species.     

Reduction of NO by activated carbon in the presence of vanadium

The NO reduction characteristics of a vanadium supported activated carbon catalyst have been examined without addition of reducing agent (i.e., ammonia, NH₃). The catalyst was prepared from commercial coconut activated carbon that was impregnated with 2.8 wt.% vanadium. The NO reduction reactions were conducted under conditions with 3% O₂ and without O₂ in a fixed bed reactor. In the condition with O₂, 84% NO conversion resulted at 360 °C, though the catalyst began to burnout at a temperature higher than 300 °C and with large quantities of CO and CO₂ being emitted. In the condition without O₂, the burnout of the catalyst was insignificant and resulted in small amounts of CO and CO₂. The NO conversion increased gradually with the reaction temperature reaching 78% at 450 °C. SEM photographs and BET measurements are useful tools for understanding the burnout phenomena with the catalyst. The burnout in the condition with O₂ resulted in the catalyst rapidly losing its activity. However, in the condition without O₂, the catalyst gradually lost its activity and finally approached a steady state. Moreover, the modified mechanism scheme of the NO reduction reactions without NH₃ and with the catalyst is described and the global rate equation for the reaction without O₂ is obtained.     

The role of carbon surface chemistry in N2O conversion to N2 over Ni catalyst supported on activated carbon

The effect of acidic treatments on N₂O reduction over Ni catalysts supported on activated carbon was systematically studied. The catalysts were characterized by N₂ adsorption, mass titration, temperature-programmed desorption (TPD), and X-ray photoelectron spectrometry (XPS). It is found that surface chemistry plays an important role in N₂O-carbon reaction catalyzed by Ni catalyst. HNO₃ treatment produces more active acidic surface groups such as carboxyl and lactone, resulting in a more uniform catalyst dispersion and higher catalytic activity. However, HCl treatment decreases active acidic groups and increases the inactive groups, playing an opposite role in the catalyst dispersion and catalytic activity. A thorough discussion of the mechanism of the N₂O catalytic reduction is made based upon results from isothermal reactions, temperature-programmed reactions (TPR) and characterization of catalysts. The effect of acidic treatment on pore structure is also discussed.     

竹制活性炭作为催化剂载体的研究

利用SEM、N₂-物理吸附和联碱滴定法等表征手段系统比较了竹质活性炭和普通竹炭与其他材质活性炭在物化性能方面的异同,同时利用CO-化学吸附考察了这些材料作为催化剂载体对负载钯催化剂金属钯分散度的影响。实验结果表明,竹质活性炭在比表面积、孔结构、灰分含量和表面基团等物化性能方面都已具备作为催化剂载体的条件,显示出成为新催化剂载体的潜力。     

Synthesis of magnetically separable adsorbents through the incorporation of protected nickel nanoparticles in an activated carbon

We present a simple and versatile route to prepare magnetically separable porous carbons from commercial activated carbons. The magnetic properties of the composite are provided by nickel nanoparticles (around 8-15 nm), which are produced within the porous network by means of the thermal treatment at 600 °C of an activated carbon impregnated with a nickel salt and sucrose. This synthetic strategy allows the magnetic nanoparticles to be protected against acid attack. The magnetic composite thus obtained exhibits a large surface area and a high pore volume. An important advantage of this composite is that exhibits, at room temperature, low coercivity (∼0.1 kOe), allowing it to be easily manipulated by means of low external magnetic fields.     

Activated carbon supported Ni-Ca: Influence of reaction parameters on activity and stability of catalyst on methane reformation

The objective of the present work was to study the influence of some reaction parameters (temperature, chemical nature of pre-treatment gas, mass catalyst) on the yield of methane reforming with carbon dioxide on Ni (5%)-Ca (1%)/AC at atmospheric pressure. The obtained results show that the best system was pre-treated under He flow at 650 °C and then following the reaction at the same temperature. It was also detected that Ca plays a co-support role inhibiting the deactivation of catalyst at long periods of reaction. It can be concluded that it is possible to employ activated carbon as support for methane dry reformation obtaining representative methane conversions up to 40% at mild experimental conditions.