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Novel techniques for the synthesis of three-way catalytic converter support materials.

机译：用于合成三元催化转化器载体材料的新技术。

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Current automobiles use catalytic converters, consisting of noble metals on an oxide support, to convert noxious engine exhaust pollutants into less harmful species. The development of mesoporous oxide supports with optimal pore geometries could enable these devises to decrease in size and weight and significantly reduce the metal loadings required to achieve optimal performance. Thus, in this work, I investigated a wide range of techniques for the synthesis of mesoporous oxides to determine if they could be adapted to ceria-zirconia-yttria mixed oxide (CZY) systems, which are the industry standard for the optimal oxide support for catalytic converter applications. Additionally, I compared and critically evaluated the catalytic performance of the CZY mixed oxides, which were synthesized from the various templating techniques. The catalytic performance test was broken up into two: catalyst activity test which was determined based on the light-off temperatures at which 50% conversion of the reacting species have been converted; and resistance to surface area loss under accelerated aging at heating rate of 20 ºC/min form 700 to 1000 ºC, with the final temperature being held fixed for 4 h.;To date, the most cost effective methods for preparing mesoporous materials are via techniques that employ templates or structure directing agents. These templates can be divided into two groups: endo-templates (i.e., soft templates, such as surfactants, dendrimers, and block copolymers) and exo-templates (i.e., hard templates, such as porous carbons and resins). The soft templating techniques generally involve both sol-gel and templating methods, while the hard templates required no sol-gel chemistry to achieve the desired templating effect. The precursors for ceria, zirconia, and yttria used were cerium (III) nitrate hexahydrate, zirconyl nitrate, and yttrium nitrate hexahydrate, respectively. The mesoporous CZY materials that were synthesized had surface area values that were between 40 and 120 m2/g and pore diameters that range from 2.2 to 9.0 nm after calcination in air from ambient temperature to 600 °C at heating rates varied from 1 to 20 °C /min, with the final temperature being maintained for 4 h.;The novel CZY oxides that were prepared from the different templating techniques were characterized using nitrogen physisorption to determine the Brunauer--Emmett--Teller (BET) surface area and the Barrett--Joyner--Halenda (BJH) pore size distribution. Samples that showed some promise were further examined by transmission electron microscopy (TEM) to study the morphology of the structure; scanning electron microscopy (SEM) to study the bulk surface structure; thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) to determine physical and chemical changes occurring during calcination; elemental analysis to determine composition; powder X-ray diffraction (PXD) to determine the existence of crystalline structure; and small angle X-ray diffraction (SAXD) to determine the occurrence of mesoscale ordering of repeating units. Finally, selected samples underwent catalytic testing under simulated exhaust conditions. The results of the tests showed that CZY materials synthesized using sol-gel methods with the Pluronic P123 soft template were the most active (i.e., had the lowest light off temperature), while CZY material with least loss of surface area after accelerated aging from 700 to1000 ºC was the polymeric resin templated CZY materials.
机译：当前的汽车使用由在氧化物载体上的贵金属组成的催化转化器将有害的发动机废气污染物转化为危害较小的物质。具有最佳孔几何形状的中孔氧化物载体的开发可使这些装置减小尺寸和重量，并显着降低获得最佳性能所需的金属负载。因此，在这项工作中，我研究了多种合成介孔氧化物的技术，以确定它们是否可以适应二氧化铈-氧化锆-氧化钇混合氧化物（CZY）系统，这是获得最佳氧化物支持的工业标准。催化转化器的应用。此外，我比较并严格评估了由各种模板技术合成的CZY混合氧化物的催化性能。催化性能测试分为两部分：催化剂活性测试，其基于起燃温度确定，在该起燃温度下，反应物种的转化率已转化为50％。以及在700至1000℃的20℃/ min加热速率下加速老化时的表面积损失抗性，最终温度保持固定4 h 。；迄今为止，制备中孔材料最经济有效的方法是通过技术使用模板或结构指导代理。这些模板可以分为两组：内模板（即，软模板，例如表面活性剂，树状聚合物和嵌段共聚物）和外模板（即，硬模板，例如多孔碳和树脂）。软模板技术通常涉及溶胶-凝胶和模板方法，而硬模板不需要溶胶-凝胶化学即可达到所需的模板效果。所使用的二氧化铈，氧化锆和氧化钇的前体分别是六水合硝酸铈（III），硝酸氧锆和六水合硝酸钇。合成的介孔CZY材料的表面积值介于40至120 m2 / g之间，在环境温度至600°C的空气中以1至20°的升温速率煅烧后，其孔径范围为2.2至9.0 nm。 C / min，最终温度保持4小时;使用氮物理吸附法对由不同模板技术制备的新型CZY氧化物进行表征，以确定Brunauer-Emmett-Teller（BET）表面积和Barrett --Joyner--Halenda（BJH）孔径分布。表现出某些希望的样品通过透射电子显微镜（TEM）进行了进一步检查，以研究结构的形态。扫描电子显微镜（SEM）研究整体表面结构；热重分析（TGA）和差示扫描量热法（DSC）确定煅烧过程中发生的物理和化学变化；元素分析以确定组成；粉末X射线衍射（PXD）以确定晶体结构的存在；和小角度X射线衍射（SAXD）来确定重复单元的中尺度有序化。最后，选定的样品在模拟排气条件下进行了催化测试。测试结果表明，使用溶胶凝胶法与Pluronic P123软模板合成的CZY材料活性最高（即起燃温度最低），而加速老化后的CZY材料（从700开始老化）损失最小。聚合树脂模板化的CZY材料达到1000ºC。

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