EFRI DCheM: Precise but Tunable Reactions Through Tunably Precise Surfaces

利用地理上分布的资源，如生物质、搁浅天然气、沼气和城市固体废物，进行本地化的清洁化学制造，有可能改变美国国内制造业的格局。然而，这些资源的产量通常相对较少，因此收集和运输到大型集中化工厂是不切实际的，而且往往不经济。此外，集中式工厂——由于其规模——被限制在稳定条件下运行，在工艺条件、原料可变性和最终产品方面几乎没有灵活性。相比之下，小型反应器系统放宽了这些限制，因此，较小规模的分布式化学制造（DCheM）系统提供了快速改变操作条件以提高处理效率和响应原料变化的新机会。因此，该项目的总体目标是通过调节反应器的操作参数来开发一种全新的催化反应器设计方法，以提高反应速率、产物选择性和催化剂寿命。该项目侧重于甲烷和乙烷的增值，这是天然气的主要成分，但可以将不同质量的分布式原料转化为高价值液体产品的瞬态运行、灵活的小型反应器的概念是广泛适用的。这种反应器的发展为分布在美国各地的丰富资源的点源化学加工打开了大门，从而改变了区域经济以及整个化学制造业的格局。该项目介绍了一种新的动态振荡催化反应器，它可以周期性地调节催化现场的反应气体环境。目标是在基本层面上确定催化反应器的设计和操作参数，以提高速率、选择性和催化剂寿命，而不是在稳态运行中达到的水平。选择甲烷氧化重整（MOR）和乙烷氧化脱氢（EODH）作为两个探针反应，这两个反应在放热/吸热操作条件下都具有可调的反应化学性质。为了证明这种增强的性能，在MOR的氧化和还原催化半循环中，基本表面过程的覆盖依赖性将通过密度泛函理论（DFT）、从头算分子动力学（AIMD）和动力学蒙特卡罗（kMC）方法进行表征。这将与产品的超灵敏实验时间分析（TAP）相结合，以揭示与经典稳态反应速率动力学不同的表面瞬态。时间步骤的解析将通过利用外部诱导的周期性进料调制的新反应途径来描述操作。调制的影响将在微反应器和单片反应器中进行实验证明，并结合原位技术来证明提高速率/选择性和寿命的途径。最后，通过描述反应堆性能和预测最优动态运行条件，建立反应堆规模模型以统一实验和理论。总的来说，本文提出的实验-计算相结合的方法将建立一种新的多相催化策略，并通过创新的反应工程概念，突破Sabatier火山所表现出的传统稳态热力学/动力学极限。该项目将包括教育和外展活动，强调为代表性不足的学生群体提供机会。为此，该项目将聘请一名合作者，协调所有项目研究人员参加的多样性研讨会。合作伙伴还将通过参加旨在促进STEM教育和劳动力发展多样性的会议，招募代表性不足的少数族裔学生。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The use of geographically distributed resources such as biomass, stranded natural gas, biogas and municipal solid waste for localizable, clean chemical manufacturing has the potential to transform the U.S. domestic manufacturing landscape. However, those resources are typically produced in relatively small quantities that make their collection and transport to large centralized chemical plants impractical and often uneconomical. In addition, the centralized plants – because of their size – are constrained to operating under steady conditions with little flexibility with respect to process conditions, feedstock variability, and end products. In contrast, small-scale reactor systems relax such constraints and therefore, the smaller scale of distributed chemical manufacturing (DCheM) systems offers new opportunities to change operating conditions rapidly to increase processing efficiency and respond to feedstock variability. The overarching goal of the project is thus to develop a radically new approach to catalytic reactor design by modulating reactor operating parameters to achieve improved rates, product selectivity, and catalyst lifetime. The project focuses on valorizing methane and ethane, the main components of natural gas, but the concept of transiently-operated, flexible, small-scale reactors that can convert distributed feedstocks of different qualities to higher-value liquid products is broadly applicable. The development of such reactors opens the door to point-of-source chemical processing of abundant resources distributed throughout the U.S., thereby transforming regional economies as well as the overall chemical manufacturing landscape.The project introduces a new dynamically-oscillated catalytic reactor that periodically modulates the reacting gas environment about a catalytic site. The goal is to identify – at a fundamental level – catalytic reactor design and operating parameters that improve rates, selectivity, and catalyst longevity beyond levels accessible in steady-state operation. Methane oxidative reforming (MOR) and ethane oxidative dehydrogenation (EODH) are chosen as two probe reactions, both having tunable reaction chemistry between exothermic/endothermic operating conditions. To demonstrate the enhanced performance, the coverage dependence of fundamental surface processes during the oxidation and reduction catalytic half-cycles for MOR will be characterized via density functional theory (DFT), ab-initio molecular dynamics (AIMD), and kinetic Monte Carlo (kMC) methods. This will be coupled with ultrasensitive experimental temporal analysis of products (TAP) to reveal surface transients that diverge from classical steady-state reaction rate kinetics. The resolution of the temporal steps will describe operation through new reaction pathways that utilize externally induced periodic feed modulations. The effect of modulation will be demonstrated experimentally in micro- and monolithic-reactors coupled with in situ techniques to demonstrate pathways to rate/selectivity and longevity enhancements. Finally, a reactor-scale model will be built to unify the experiments and theory by describing reactor performance and predicting optimal dynamical operating conditions. Collectively, the combined experimental-computational approach pro-posed here will establish a new strategy for heterogeneous catalysis and push beyond the conventional steady-state thermodynamic/kinetic limits manifested in the Sabatier volcano by using innovative reaction engineering concepts. The project will include education and outreach activities emphasizing opportunities for underrepresented student groups. To this end, the project will engage a collaborator to coordinate diversity workshops that will engage all of the project researchers. The collaborator will also recruit underrepresented minority students through attending conferences targeted at promoting diversity in STEM education and workforce development.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.