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

在这个由化学系化学结构动力学和机制（CSDM-A）项目资助的项目中，弗吉尼亚大学的Ian Harrison教授正在使用先进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，一个感兴趣的反应是二氧化碳（CO2）和氢原子（H）之间的反应，当CO2和H首先吸附在铜表面上时（换句话说，金属表面充当催化剂），该反应可以被加速。 Harrison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下一代催化剂和催化工艺的设计。 通过这种方式，这项研究可能有助于推进催化技术，以更有效地利用天然气生产产品，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使用二氧化碳作为化学原料。这项研究的更广泛的影响源于研究生和本科生在设计和建造先进的实验仪器和复杂的计算机建模的培训。推广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读本科生提供更多的研究机会。激活化学吸附的动力学探测使用加热的溢出分子束撞击在单晶金属表面上测量解离/关联粘附概率，S（Tg，Ts;角），作为气体表面温度和入射角的函数。从脉冲激光辅助热缔合/解离解吸（LAAD/拉德）反应在表面的产物状态分布的新测量将解决激活化学吸附从反应屏障的表面侧开始。通过详细平衡的原理解释，LAAD/拉德测量定义了平移能量分辨的热粘附概率S（Et，T;角度），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的活化粘附概率，甚至区分化学特异性反应途径，例如乙烷解离化学吸附中的C-C或C-H键断裂。实验测量，再加上动态偏微正则理论建模，被用来测试和量化的催化反应性的动态控制，并将这种动态控制到特定的过渡态属性。

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.