Size and Shape Control in Heterogeneous Catalysis Synthesis

传统上，不饱和有机物中的温和催化反应，如双键氢化和异构化，被认为不依赖于催化剂表面的结构。然而，这一结论是基于使用由尺寸和形状分布广泛的金属颗粒组成的不明确催化剂的研究；最近的催化和表面科学实验表明，这些体系实际上可能表现出一定的结构敏感性。我们的假设是，轻度催化反应的选择性可以通过精心设计具有明确结构的催化剂来控制。该提案描述了通过使用新的纳米技术来开发尺寸和形状选定催化剂的研究，以验证这一假设。具体而言，将开发新的胶体和溶胶-凝胶合成路线，以生产具有窄分布尺寸和明确形状的支撑金属（Pt）颗粒。这项工作将分三个阶段进行。(1)首先，根据El-Sayed教授的研究小组最近的一份报告，将使用胶体程序制备具有明确大小和形状的金属颗粒，包括四面体和立方形状。大小和形状将被独立控制，以便单独探测它们对催化的影响。(2)接下来，这些颗粒将分散在高表面积固体上，并被激活进行多相催化。这里将首先尝试三种方法：浸渍，用更容易去除的巯基取代聚合物，以及在胶体颗粒存在的情况下原位溶胶-凝胶生长氧化物。(3)最后，将对这些催化剂进行表征，并测试它们对两个特定反应的促进作用：不饱和醛选择性加氢成不饱和醇，以及烯烃双键的顺反异构化。之所以选择这些反应，是因为人们相信，暴露在四面体粒子中的（111）表面可能会选择性地促进这些反应（与终止立方粒子的（100）平面相反）。最终，我们的目标是将新型合成方法的使用与从模型系统研究中获得的理解相结合，在控制其尺寸和形状的基础上，为轻度催化过程设计选择性金属负载催化剂。我们的工作所产生的一般基础知识也可能适用于更广泛的合成和催化问题，包括催化中的胶体和溶胶-凝胶化学以及结构敏感性。我们的方法的价值在于，它结合了三个不同领域的知识：胶体化学家、催化剂开发人员和表面科学家。如果我们的假设被证明是正确的，它可能会对新的工业流程的设计产生巨大的影响，例如，提高食品工业的脂肪生产（在食品工业中，反式烯烃因其对健康不利而被避免使用），或推进精细化学合成的新路线。我们的项目也将有助于更好地理解支撑胶体颗粒的化学性质，以及影响表面选择性的化学动力学因素。将开发具有潜在广泛吸引力的新实验技术，如合成定义良好的负载催化剂。从这项工作中获得的知识也可以用于教育目的，通过提供数据来说明本科和研究生课程中基本的固态合成和催化原理。将加强与拉丁美洲研究小组的合作，并将大力鼓励来自代表性不足群体（特别是西班牙裔）的学生参与研究。

CBET-0752142ZaeraTraditionally, mild catalytic reactions such as double-bond hydrogenations and isomerizations in unsaturated organics have been assumed to not depend on the structure of the surface of the catalyst. However, that conclusion has been based on studies using ill-defined catalysts consisting of metal particles with wide distributions of sizes and shapes; recent catalysis and surface-science experiments indicate that these systems may in fact display some structure sensitivity. Our hypothesis is that selectivity in mild catalytic reactions may be controlled by careful design of catalysts with well-defined structures.This proposal describes research to develop size and shape selected catalysts by using new nanotechnologies in order to test that hypothesis. Specifically, novel colloidal and sol-gel synthetic routes will be developed to produce supported metal (Pt) particles with narrow distributions of sizes and well-defined shapes. This work will be performed in three stages. (1) First, metal particles with well-defined sizes and shapes, including tetrahedral and cubic forms, will be prepared using colloidal procedures deriving from a recent report by the research group of Prof. El-Sayed. Size and shape will be independently controlled in order to individually probe their effect on catalysis. (2) Next, those particles will be dispersed on high-surface-area solids and activated for heterogeneous catalysis. Three approaches will be attempted here at first: impregnation, polymer displacement by easier-to-remove thiol groups, and in-situ sol-gel growth of oxides in the presence of the colloidal particles. (3) Finally, these catalysts will be characterized, and tested for the promotion of two specific reactions: the selective hydrogenation of unsaturated aldehydes to unsaturated alcohols, and the cis-trans isomerization of double bonds in olefins. These reactions have been chosen because it is believed that they may be selectively promoted by the (111) surface facets exposed in tetrahedral particles (in contrast with the (100) planes that terminate the cubic particles).Ultimately, we aim to combine the use of novel synthetic methods with the understanding achieved from studies with model systems to design selective metal supported catalysts for mild catalytic processes based on control of their size and shape. The general basic knowledge generated by our work is also likely to apply to a broader set of synthetic and catalytic issues involving colloidal and sol-gel chemistry and structure sensitivity in catalysis. The value of our approach is that it combines knowledge developed by three separate communities, colloidal chemists, catalyst developers, and surface scientists.If our hypothesis is proven true, it may have great repercussions on the design of new industrial processes, to, for instance, improve fat production in the food industry (where trans olefins are to be avoided because of their adverse health effects), or advance new routes for fine chemical synthesis. Our project will also contribute to the development of a better basic understanding of the chemistry of supported colloidal particles, and of the chemical kinetic factors that affect selectivity on surfaces. New experimental technology with potential broad appeal such as the synthesis of well-defined supported catalysts will be developed. The knowledge deriving from this work may also be of great use for educational purposes by providing data to illustrate basic solid-state synthesis and catalysis principles in undergraduate and graduate classes. Collaborations with Latin American research groups will be forged, and student participation from underrepresented groups in research (Hispanics in particular) will be strongly pursued.