Towards Dynamical Control over Gas-Surface Reactivity: Light Alkane and Carbon Dioxide Activation at Catalytic Metal Surfares

在这个由化学部化学结构动力学和机理（CSDM-A）项目资助的项目中，弗吉尼亚大学的Ian Harrison教授使用复杂的激光和分子束技术，结合理论建模，研究天然气分子和二氧化碳与金属表面的反应。例如，我们感兴趣的一个反应是二氧化碳（CO2）和氢原子(H)之间的反应，当二氧化碳和氢原子首先吸附在铜表面时（换句话说，金属表面起催化剂的作用），这个反应就会加速。哈里森教授的研究旨在揭示分子和/或原子与金属表面碰撞时形成的初始结构如何决定反应产物和反应速率。了解分子表面反应的细节可能有助于设计下一代催化剂和催化过程。通过这种方式，该研究可能有助于推动催化技术的发展，以更有效地从天然气中生产产品，转化目前消耗约2%的全球能源，并以减少温室气体净排放的方式将二氧化碳用作化学原料。本研究的进一步广泛影响源于对研究生和本科生在设计和构建先进实验仪器和复杂计算机建模方面的培训。拓展活动包括在当地小学和中学授课和实验室演示，并为少数民族和联邦工作学习本科生提供更多的研究机会。利用加热的射流分子束撞击单晶金属表面来探测活化化学吸附的动力学，以测量解离/结合粘附概率S（Tg, Ts；角）作为气体表面温度和入射角的函数。脉冲激光辅助热结合/解离解吸（LAAD/LADD）表面反应的产物状态分布的新测量将解决从反应垒的表面侧开始的活化化学吸附。通过详细平衡原理解释，LAAD/LADD测量定义了平动能量分解的热粘附概率S(Et， T; angle)，与热驱动的工业催化直接相关。激光方法提供了独特的新机会来表征极低激活粘附概率，甚至区分化学特异性反应途径，如乙烷解离化学吸附中的C-C或C-H键裂解。实验测量，加上动态偏倚的微规范理论模型，被用于测试和量化对催化反应性的动力学控制，并将这种动力学控制与特定的过渡态性质联系起来。

In this project funded by the Chemical Structure Dynamics and Mechanism (CSDM-A) program of the Chemistry Division, Professor Ian Harrison of the University of Virginia is using sophisticated laser and molecular beam techniques, coupled with theoretical modeling, to study the reactions of natural gas molecules and carbon dioxide with metal surfaces. For example, one reaction of interest is that between carbon dioxide (CO2) and hydrogen atoms (H), which can be accelerated when CO2 and H first adsorb on a copper surface (in other words, the metal surface is acting as a catalyst). Prof. Harrison's research aims to reveal how the initial structures formed when molecules and/or atoms collide with a metal surface determine the products of the reaction and the rates of the reaction. Understanding the details of molecule-surface reactions may aid the design of next generation catalysts and catalytic processes. In this way, the research may help advance catalytic technologies to more efficiently make products from natural gas, transformations that currently consume approximately 2% of global energy, and to use carbon dioxide as a chemical feedstock in ways that would reduce net greenhouse gas emissions. Further broader impacts of this research stem from the training of graduate and undergraduate students in the design and construction of advanced experimental instrumentation and complex computer modeling. Outreach activities include giving lessons and lab demonstrations at local elementary and middle schools and providing expanded research opportunities to minority and Federal Work Study undergraduate students. The dynamics of activated chemisorption are probed using a heated effusive molecular beam impinging on a single crystal metal surface to measure dissociative/associative sticking probabilities, S(Tg, Ts; angle), as functions of gas & surface temperatures and angle of incidence. New measurements of product state distributions from pulsed laser assisted thermal associative/dissociative desorption (LAAD/LADD) reactions at surfaces will address activated chemisorption beginning from the surface side of the reaction barrier. Interpreted through the principle of detailed balance, the LAAD/LADD measurements define translational energy- resolved thermal sticking probabilities S(Et, T; angle), directly relevant to thermally-driven industrial catalysis. The laser methods provide unique new opportunities to characterize extremely low activated sticking probabilities and to even discriminate between chemically- specific reaction pathways such as C-C or C-H bond cleavage in ethane dissociative chemisorption. The experimental measurements, coupled with dynamically-biased microcanonical theoretical modeling, are being used to test and quantify the control of dynamics over catalytic reactivity, and to relate this dynamical control to specific transition state properties.