CAREER: Modulation of Kinetic Dispersion at the Single Molecule Level on Individual Catalytic Nanoparticles

技术/科学价值催化对工业化国家的经济和技术的影响怎么夸大都不为过。令人惊讶的是，我们目前关于催化剂设计的知识往往是相当初级的，这种催化剂能够以最小的环境影响形成所需的产品。多相催化是极其复杂的，催化剂周转过程中催化剂表面位置的动态变化影响着反应的动力学结果。研究具有单一翻转分辨率的纳米粒子催化剂将提高我们在分子水平上对动力学分散的起源的理解，并将为如何利用这些信息来设计具有最佳活性和选择性的催化剂提供见解。宾夕法尼亚州立大学的Robert M.Rioux将在NSF教师早期职业发展(Career)计划奖下提供这一水平的学习。Rioux将这种情况类比为生物系统中的情况。单分子测量彻底改变了生物学家思考结构和功能的方式，因为它揭示了结构是动态的，而不是静态的，结构的变化发生在功能上。在多相催化剂体系中，实验研究也提供了直接证据，表明负责催化周转的表面原子是动态的，而不是静态的。然而，测量的反应性是由于表面原子的集合，结构动力学还没有与反应性测量相结合。了解动态结构变化(流动性)如何与功能相结合对于下一代催化剂的设计至关重要，因为这是对催化剂周转的催化实体的直接洞察。Rioux将利用具有单一周转分辨率的单纳米颗粒方法，结合使用新量热法和化学滴定表征催化固液界面，来研究结构与功能之间的关系。利用转化为荧光团的亲荧光分子进行的实验研究将被用来检验动态结构变化之间的关系。无论这些变化与纳米颗粒本身或初级溶剂化层--以及单分子周转轨迹--有关。本课程将考察催化剂的各种变量，如颗粒大小及其与不同亲和力和化学性质的吸附物的后续修饰。反应速度受温度的影响很大，并将评估温度相关的流变性对催化过程的影响。与建议的速率表达式相关的动力学和热力学参数的分布将在单分子水平上进行评估，并与系综等效物进行比较。这项工作还将使用一种非荧光反应物来研究同时周转对活性和选择性的空间依赖性，该反应物产生两种具有不同发射特性的产品。研究结果将为催化/纳米粒子社区提供关于催化周转动力学和动力学的明确的结构-功能关系。通过单纳米颗粒测量获得的对催化过程的基本洞察应该能够通过提供结构对功能的影响的动态而不是静态的图像来实现更高效的催化剂设计。这份NSF职业提案支持的教育活动侧重于发展一年级研讨会(FYS)，以吸引和留住特别是化学工程专业的本科生。新开发的FYS将整合目前参与AIChE ChemE汽车项目的皮？S，并提供？动手？为大一/大二女生提供辅导体验。FYS将包括对宾夕法尼亚联邦校园的外联活动。州，在那里，女性(和男性)学生没有机会参加以化学工程为主题的FYS。PI将与他的研究生一起前往英联邦校园进行现场实践？示威游行。

Technical/Scientific MeritThe impact of catalysis on the economy and technology of industrialized countries is impossible to overstate. It is surprising that our current knowledge of catalyst design that leads to a catalyst capable of desired product formation with minimal environmental impact is often quite rudimentary. Heterogeneous catalysis is extremely complex and the dynamics at the catalyst surface sites during catalytic turnover influences the kinetic outcome of the reaction. Studying nanoparticle catalysts a single particle at a time with single turnover resolution will improve our molecular level understanding of the origins of kinetic dispersion, and will provide insights on how to utilize this information to design catalysts with optimized activity and selectivity. Robert M. Rioux of The Pennsylvania State University will provide this level of study under a NSF Faculty Early Career Development (CAREER) Program Award. Rioux analogizes the situation to that in biological systems. Single molecule measurements have revolutionized how biologists think about structure and function since it was revealed structure is dynamic rather static with changes in structure occurring while functioning. In heterogeneous catalyst systems, experimental studies have also provided direct evidence that surface atoms responsible for catalytic turnover are dynamic, rather than static. However, measured reactivity is due to an ensemble of surface atoms, and structural dynamics have not been coupled with reactivity measurements. Understanding how dynamic structural changes (fluxionality) couple to function is critical to the design of next generation catalysts since this is direct insight into the catalytic entity responsible for catalytic turnover. Rioux will investigate structure-function relationships utilizing single nanoparticle methods with single turnover resolution coupled with characterization of the catalytic solid-liquid interface with novel calorimetric methods and chemical titration. Experimental studies utilizing pro-fluorescent molecules which convert to fluorophores will be utilized to examine the relationship between dynamic structural changes ? whether these changes are associated with the nanoparticle itself or the primary solvation layer -- and single molecule turnover trajectories. Catalyst variables such as particle size and their subsequent modification with adsorbates of varying affinity and chemical character will be examined. The rate of reaction is influenced drastically by temperature and the influence of temperature-dependent fluxionality on the catalytic processes will be evaluated. Distribution of kinetic and thermodynamic parameters associated with proposed rate expressions will be assessed at the single molecule level and compared with ensemble equivalents. This work will additionally examine the spatial dependence of simultaneous turnover on activity and selectivity using a non-fluorescent reactant that produces two products with different emission characteristics. The relationship between reaction selectivity and location on the catalytic nanoparticle will be assessed with correlative microscopy.Broader ImpactsThe results of the proposed research will provide the catalysis/nanoparticle community with unambiguous structure-function relationships regarding the kinetics and dynamics of catalytic turnover. The fundamental insight into catalytic processes gained from single nanoparticle measurements should enable more efficient catalyst design by providing a dynamic, rather than static picture of the influence of structure on function.Educational activities supported by this NSF CAREER proposal focus on the development of a first year seminar (FYS) to attract and retain particularly undergraduate female students in the chemical engineering major. The newly-developed FYS will integrate the PI?s current involvement in AIChE ChemE car project and provide a ?hands-on? mentored experience for freshmen/sophomore female students. The FYS will include a component of outreach to the commonwealth campuses of Penn. State, where female (and male) students do not have the opportunity to participate in a chemical engineering themed FYS. The PI along with his graduate students will travel to the commonwealth campuses for on-site, ?hands-on? demonstrations.