ABSTRACT

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.

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