CAREER: Reaction Kinetics Analysis of the Lebedev Process

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The project explores the potential of using biorenewable ethanol as an alternative to conventional petroleum resources for production of 1,3-Butadiene (BD) - an important chemical precursor used to produce synthetic rubbers utilized in car tires, paper coatings, textile backings, and adhesives. Recent shifts in petroleum resources have placed pressure on the BD market, opening the door to on-purpose production of BD. A particularly promising technology is the Lebedev process which manufactures BD from ethanol. However, the process relies on a complex, multicomponent catalyst and suffers from low product yields. The project will develop a molecular-level picture of the reaction network used to produce BD from ethanol, which in turn is important for developing new catalysts that can achieve high BD yields. Thus, the project has potential to ensure security and U.S. competitiveness in BD production while supporting the clean-energy transition to biorenewable feedstocks. Additionally, the investigator will develop new course materials to teach undergraduate students about catalytic reactor design and biobased chemicals production. The project team will also develop a module to educate high school students and the public about the production of renewable chemicals from woody biomass.Following on the early work of Union Carbide, many groups have used MgO-SiO2 as a low-cost platform from which to develop next-generation catalysts for the Lebedev process. However, to date a rigorous reaction kinetics analysis of BD production by MgO-SiO2 has not been performed. Based on recently published results from the investigator’s team, coupled with observations in the literature, the rate of BD formation over pure MgO-SiO2 catalysts is hypothesized to be controlled by ethanol dehydrogenation, while selectivity to BD in the presence of transition metal promoters is hypothesized to result from C-C bond formation catalyzed by acid-base site pairs. The literature is conflicted about the C-C coupling mechanism and the nature of the requisite active sites, which the study will clarify in three main thrusts. First, steady-state reaction kinetics measurements using model MgO-SiO2 catalysts containing specific types of acid-base site pairs will be used to identify rate-controlling steps and to clarify which sites are responsible for the kinetically significant reactions in BD production. Next, these catalysts will be spectroscopically characterized by FTIR, XPS, LEIS, and SSNMR to identify site requirements and abundant surface intermediates. Finally, a microkinetic model will be used to unify the macroscopic kinetics observations with mechanistic insight provided by kinetic isotope effect and isotope tracer studies and DFT calculations.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.