Size and Shape Control in Heterogeneous Catalysis Synthesis

传统上，温和的催化反应，如不饱和有机物中的双键加氢和异构化，被认为不依赖于催化剂表面的结构。然而，这一结论是基于对由大小和形状广泛分布的金属颗粒组成的定义不明确的催化剂的研究；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，温和催化反应中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。这项建议描述了利用新的纳米技术来开发选定催化剂的尺寸和形状的研究，以验证这一假设。具体地说，将开发新的胶体和溶胶凝胶合成路线，以生产尺寸分布窄、形状明确的负载型金属(铂)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尺寸和形状明确的金属颗粒，包括四面体和立方体。大小和形状将独立控制，以单独探讨它们对催化的影响。(2)下一步，这些颗粒将被分散在高比表面积的固体上，并被激活以用于多相催化。这里将首先尝试三种方法：浸渍，通过更容易去除的硫醇基团置换聚合物，以及在胶体颗粒存在的情况下氧化物的原位溶胶-凝胶生长。(3)最后，对这些催化剂进行了表征，并测试了它们对两个特定反应的促进作用：不饱和醛选择加氢为不饱和醇和烯烃中双键的顺反异构化。之所以选择这些反应，是因为人们认为它们可能被暴露在四面体粒子中的(111)表面(而不是终止立方体粒子的(100)面)选择性地促进。最终，我们的目标是将新的合成方法的使用与通过模型系统研究所获得的理解相结合，基于对其大小和形状的控制来设计用于温和催化过程的选择性金属载体催化剂。我们的工作产生的一般基础知识也可能应用于更广泛的合成和催化问题，涉及胶体和溶胶凝胶化学以及催化中的结构敏感性。我们方法的价值在于，它结合了胶体化学家、催化剂开发人员和表面科学家这三个不同群体开发的知识。如果我们的假设被证明是正确的，它可能会对新的工业工艺的设计产生巨大影响，例如，提高食品工业的脂肪生产(由于反式烯烃对健康的不利影响，应避免反式烯烃)，或推进精细化学合成的新路线。我们的项目还将有助于更好地了解负载型胶体颗粒的化学组成，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的实验技术，如合成定义明确的负载型催化剂。通过在本科生和研究生课堂上提供数据来说明固体合成和催化的基本原理，从这项工作中获得的知识也可能对教育目的有很大的帮助。将建立与拉丁美洲研究小组的合作，并将大力推动代表不足的群体(特别是拉美裔美国人)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.