Temperature Jump Infrared Electrochemical Spectroscopy (TIR-SEC) of Catalytic Intermediates

在这个由化学系化学结构、动力学和机制-A(CSDM-A)计划资助的项目中，宾夕法尼亚州立大学的约翰·阿斯伯里教授正在使用先进的激光技术来了解如何控制催化材料表面的复杂反应。许多缓慢的化学反应可以通过在催化剂上施加电压来加速--催化剂是用来指导反应过程的材料。在这个项目中，开发了催化剂来加速和指导反应，这些反应可以将二氧化碳还原为燃料，或者可以将氮气还原为化肥用的氨。这样的反应可以在未来建立可持续的能源和农业系统方面发挥重要作用。这些反应通过将多个电子和多个质子转移到在反应过程中形成的产物来进行。每次将电子和质子添加到产品分子中，它们的化学性质都会发生变化。这个项目提供了关于催化剂表面如何发生化学反应的见解，以及它们表面的什么类型的位置可以最有效地指导每个电子和质子转移步骤。从事这一研究项目的学生在激光技术、电化学和催化材料设计方面获得了宝贵的经验。这项工作的更广泛影响包括开发催化剂以更有效地将二氧化碳和氮气等气体转化为更可持续的能源和农业系统的有用产品的潜在社会效益，以及培训学生在操作条件下进行催化研究的先进光谱和电化学仪器设计的机会。这个研究项目中开发的一些光谱技术将被引入本科教学实验室。该项目专注于多个电子和质子转移步骤中涉及的时间分辨反应中间体，这些步骤导致二氧化碳转化为烷烃，气态氮转化为氨。反应中间体通过它们在催化剂表面形成时的中红外振动特征来识别，催化剂表面沉积在衰减的全内反射中红外波导上。催化剂被结合到运行的电化学池中，允许在运行的电化学势下监测化学中间体。催化反应是通过施加电化学势和短激光脉冲来触发的，紧随其后的是通过波导传播的中红外探测脉冲。波导由硅棱镜组成，催化剂和工作电极沉积在硅棱镜上，浸泡在电解液中，密封在容器中，以容纳参与反应的气体。化学中间体的光谱观察与电催化剂的活性相关，以深入了解反应不同阶段的催化中间体如何影响整体活性和选择性。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

In this project funded by the Chemical Structure, Dynamics, and Mechanisms-A (CSDM-A) program of the Chemistry Division, Professor John Asbury of The Pennsylvania State University is using advanced laser techniques to understand how to control complex reactions at the surfaces of catalytic materials. Many sluggish chemical reactions can be accelerated by applying voltage to catalysts - materials that are designed to direct the course of the reactions. In this project, catalysts are developed to accelerate and direct reactions that can reduce carbon dioxide to fuels or that can reduce nitrogen gas to ammonia for fertilizers. Such reactions can play important roles in building sustainable energy and agricultural systems in the future. The reactions occur by transferring multiple electrons and multiple protons to the products that form during the course of the reactions. Each time electrons and protons are added to the product molecules, their chemical properties change. This project is providing insights into how chemical reactions occur at the surfaces of catalysts and what types of sites on their surfaces can most effectively direct each electron and proton transfer step. Students engaged in this research project are gaining valuable experience in state of the art laser techniques, electrochemistry and catalytic materials design. The broader impacts of this work include potential societal benefits from the development of catalysts to more efficiently convert gases such as carbon dioxide and nitrogen to useful products for more sustainable energy and agricultural systems as well as opportunities to train students in the design of advanced spectroscopy and electrochemical instrumentation for catalytic studies under operating conditions. Some of the spectroscopy techniques developed in this research project will be introduced into undergraduate teaching laboratories.The project focuses on time-resolving reaction intermediates involved in multiple electron and proton transfer steps that lead to the conversion of carbon dioxide to alkanes and gaseous nitrogen to ammonia. The reaction intermediates are identified through their mid-infrared vibrational signatures as they form on catalyst surfaces that are deposited onto attenuated total internal reflection mid-infrared waveguides. The catalysts are incorporated into operating electrochemical cells that allow chemical intermediates to be monitored under operating electrochemical potentials. The catalytic reactions are triggered by application of an electrochemical potential and a short laser pulse that are followed by a mid-infrared probe pulse that propagates through the waveguide. The waveguide consists of a silicon prism on which the catalyst and working electrode are deposited, immersed in an electrolyte, and sealed in a vessel to contain gases that are involved in the reactions. The spectroscopic observations of chemical intermediates are correlated with the activity of the electrocatalysts to provide insight about how catalytic intermediates at various stages of the reactions influence the overall activity and selectivity.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.