EFRI DCheM: Precise but Tunable Reactions Through Tunably Precise Surfaces

利用地理上分布的资源，如生物质、滞留天然气、沼气和城市固体废物，进行本地化、清洁的化学制造，有可能改变美国国内制造业的格局。然而，这些资源通常以相对较小的数量生产，这使得收集和运输到大型集中式化工厂是不切实际的，而且往往不划算。此外，集中式工厂由于其规模的限制，只能在稳定的条件下运行，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，小型反应堆系统放松了这些限制，因此，规模较小的分布式化学制造(DCheM)系统提供了快速改变操作条件以提高处理效率和对原料变异性做出反应的新机会。因此，该项目的总体目标是通过调整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，以实现更高的速率、产品选择性和催化剂寿命。该项目的重点是使天然气的主要成分甲烷和乙烷作价，但可以将不同质量的分布式原料转化为更高价值的液体产品的瞬时运行、灵活的小型反应堆的概念广泛适用。这种反应器的开发打开了对分布在美国各地的丰富资源进行点源化学加工的大门，从而改变了地区经济和整个化学制造环境。该项目引入了一种新的动态振荡催化反应器，它周期性地调节催化场所周围的反应气体环境。其目标是在基本水平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，使其超过稳态操作中可以达到的水平。甲烷氧化重整反应(MOR)和乙烷氧化脱氢反应(EODH)被选为两个探针反应，都具有放热/吸热操作条件可调的反应化学。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)方法表征了MOR氧化和还原催化半周期中基本表面过程的覆盖率依赖关系。这将与超灵敏的实验时间产物分析(TAP)相结合，以揭示偏离经典稳态反应速率动力学的表面瞬变。时间步骤的分辨率将描述通过利用外部诱导的周期性馈电调制的新反应路径的操作。调制效应将在微型和整体式反应器中实验演示，并结合原位技术来演示速率/选择性和寿命增强的途径。最后，将建立一个反应堆规模的模型，通过描述反应堆的性能和预测最优的动态运行条件来统一实验和理论。总而言之，这里提出的实验-计算相结合的方法将建立一种新的多相催化策略，并通过使用创新的反应工程概念来突破萨巴蒂尔火山所表现出的传统稳态热力学/动力学限制。该项目将包括教育和外联活动，强调为代表不足的学生群体提供机会。为此，该项目将聘请一名合作者来协调将吸引所有项目研究人员参加的多样性研讨会。合作者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来招收代表不足的少数族裔学生。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。

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.