CAREER: Enhanced Catalytic Phenomena via Surface Plasmon Resonant Excitation

0846725 Cronin本提案由2009年美国复苏与再投资法案（公法111-5）资助。南加州大学的Stephen Cronin得到了工程理事会化学、生物工程、环境和运输系统部门的支持（数学和物理科学理事会化学部门的共同资助），以了解等离子体共振对催化性能的影响。将探讨两个主要假设：(i)等离子体感应电场对化学活性的影响，以及（ii）等离子体感应加热对催化的影响。方法：PI将在活性（例如TiO2）和非活性载体的顶部和嵌入中产生金属纳米结构阵列。用激光以等离子体共振频率照射这些等离子体/催化纳米结构将产生巨大的等离子体电荷和驱动催化过程所需的高温。等离子体诱导的电荷比标准光学吸收产生的电荷大几个数量级，因此有可能显著提高这些催化过程的效率。此外，纳米颗粒的局部加热会产生较大的温度梯度，从而通过允许不同的化学过程并行发生而创造新的途径。这些样品的催化活性将在一个自动化的微反应器系统中进行研究，该系统可以快速评估催化纳米结构，并允许在单个芯片上测试数千种实验条件。该系统使用质谱法和拉曼光谱法对反应副产物进行现场诊断，从而实现结构特性和催化性能之间的直接关联。各种催化和几何构型的高通量筛选将使我们能够研究有关增强催化机制的几个基本问题。本提案解决的基本问题：-催化增强是热介导的，电场介导的，还是其他方式？-纳米等离子体加热产生的大温度梯度的作用/重要性是什么？-带隙能量和掺杂水平如何影响催化活性？-使等离子体诱导电荷扩散到催化表面的金属氧化膜的临界厚度是多少？-反应物、副产物和自由基的表面结合如何影响催化活性和选择性？-通过表面等离子体共振激发，催化活性理论上的最佳增强是什么？智力上的优点是将等离子体过程的理解和应用扩展到化学领域。通过系统地解决这些基本问题，PI将能够确定等离子体增强的哪些特定方面将是最有用的，哪些化学反应将从中受益最大。等离子体辅助催化的领域充满了新的和有趣的现象，但仍然知之甚少。等离子体激发为寻找新的化学途径提供了额外的自由度，例如，为三环臭氧的产生提供了自由度。本提案中提出的系统研究可能会提供对未探索的催化现象的理解，并引入广泛适用于更大科学界的新概念。更广泛的影响：洛杉矶地区高中教师的外展计划将使未被充分代表的学生了解结果，更重要的是，这项拟议的研究和洛杉矶地区大学的其他前沿研究的兴奋。在这一努力中，PI将在南加州大学和邻近的高中之间建立长期的工作关系。为本科生提供的研究项目将使他们了解科学研究的创造性和直觉性，从而使他们有信心和灵感从事科学和工程方面的职业。新的课程将创造力融入到新的纳米科学课程中，将培养出有技能和知识的学生，他们能够应对纳米技术的下一代挑战。将课堂上的头脑风暴会议纳入传统技术课程的一般方案可以应用于物理科学和工程领域的广泛学科。催化在现代工业化学中的重要性怎么强调也不为过，它几乎影响着我们经济的每一个方面。这项拟议工作的成功完成将导致一些具有科学和工业意义的未来研究。本文研究的改进的催化过程可以应用于其他科学和工程领域，以增强各种重要的化学和电化学现象。或者，这些等离子体纳米粒子可以被整合到芯片上，以驱动与阳光的吸热反应来储存能量。等离子体加热和电场增强的局部特性是为氢和甲烷燃料电池创建集成燃料源的理想选择，而无需加热整个设备。面对全球能源危机，这项工作将为寻找新颖高效的化学过程提供新的突破口。

0846725 Cronin This proposal is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Prof. Stephen Cronin at the University of Southern California is supported by the Division of Chemical, Bioengineering, Environmental, and Transport Systems in the Engineering Directorate (with co-funding from the Division of Chemistry in the Directorate for Mathematics and Physical Sciences) to develop an understanding of the effect of plasmon resonance on catalytic performance. Two main postulates will be explored: (i) the effect of plasmon-induced electric field on chemical activity, and (ii) the effect of plasmon-induced heating on catalysis. Approach: The PI will produce arrays of metal nanostructures on top of and embedded in both active (e.g., TiO2) and non-active supports. Irradiating these plasmonic/catalytic nanostructures with a laser at their plasmon resonance frequency will generate immense plasmonic charge and high temperatures needed to drive the catalytic process. The plasmon-induced charge is orders of magnitude larger than that created by standard optical absorption and therefore has the potential to dramatically improve the efficiency of these catalytic processes. Also, the local heating of the nanoparticles generates large temperature gradients, which in turn create new pathways by allowing different chemical processes to occur side by side. The catalytic activity of these samples will be studied in an automated micro-reactor system that rapidly evaluates catalytic nanostructures and permits thousands of experimental conditions to be tested on a single chip. The system measures in situ diagnostics of the reaction byproducts using mass spectrometry and Raman spectroscopy, allowing direct correlation between structural properties and catalytic performance. High throughput screening of various catalytic and geometric configurations will enable us to investigate several fundamental questions about the enhanced catalytic mechanism. Fundamental Questions Addressed in this Proposal: - Is the catalytic enhancement heat mediated, electric field mediated, or otherwise? - What is the role/importance of the large temperature gradients created by nanoplasmonic heating? - How does the bandgap energy and doping level affect the catalytic activity? - What is the critical thickness of the metal oxide film that enables the plasmon-induced charge to diffuse to the catalytic surface? - How does surface binding of reactants, byproducts, and free radicals affect the catalytic activity and selectivity? - What is the theoretical optimum enhancement in catalytic activity achievable through surface plasmon resonant excitation? The intellectual merit is to expand the understanding and applicability of plasmonic processes into the field of chemistry. By systematically addressing these fundamental questions, the PI will be able to identify which particular aspects of the plasmon enhancement will be most useful and which chemical reactions will benefit most from it. The area of plasmon assisted catalysis is rich with new and interesting phenomena that remain poorly understood. Plasmonic excitation opens up additional degrees of freedom in the search for new chemical pathways, for example, for the production of tricyclic ozone. The systematic studies put forth in this proposal will likely provide an understanding of unexplored catalytic phenomena and introduce novel concepts that are widely applicable to the larger scientific community. Broader Impacts: The outreach program to Los Angeles area high school teachers will expose underrepresented students to the results and, more importantly, the excitement of this proposed research and other cutting-edge research at universities in the Los Angeles area. In this effort, the PI will develop a long-term, working relationship between USC and its neighboring high schools. Research projects for undergraduate students will introduce them to the creative and intuitive nature of scientific research, thereby giving them the confidence and inspiration to pursue careers in science and engineering. The novel curriculum, which integrates creativity into a new nanoscience course, will produce skilled and knowledgeable students able to address the next generation of challenges in nanotechnology. The general scheme of incorporating in-class brainstorming sessions into traditionally technical curriculum can be applied to a wide range of subjects in the physical sciences and engineering. The importance of catalysis in modern industrial chemistry cannot be overstated, impacting nearly every aspect of our economy. The successful completion of this proposed work will lead to a number of future studies with scientific and industrial relevance. The improved catalytic processes investigated herein may be applicable to other fields of science and engineering to enhance various important chemical and electrochemical phenomena. Alternatively, these plasmonic nanoparticles can be incorporated onto a chip to drive endothermic reactions with sunlight for energy storage. The localized nature of plasmonic heating and electric field enhancement is ideal for creating an integrated fuel source for hydrogen and methane fuel cells, without having to heat up the entire device. In the face of the global energy crisis, this work will provide new inroads in the critical search for novel and efficient chemical processes.