Ethanol is a promising biomass-derived feedstock for conversion to products that are traditionally derived from fossil fuels, as it is currently produced at commercial scale from renewable biomass and waste sources. One industrially relevant compound that could significantly benefit from an alternative means of production, due to the shale gas boom disrupting its present fossil-derived source, is butadiene. Butadiene is one of the most high-value, high-volume compounds in the petrochemical industry. It is widely used as a precursor in the production of automobile tires and many other essential synthetic polymers. We have developed a highly efficient process for the single-step conversion of ethanol to butadiene over Ag-ZrO2/SiO2 catalysts capable of achieving yields of 70% at near complete conversion under relatively mild process conditions. In this multifunctional catalyst, Ag assists with dehydrogenation of ethanol, and Lewis acid sites (from Zr) are required for aldol condensation and MPV reduction, with acid sites contributing to necessary dehydration of intermediates as well as the formation of unwanted ethanol dehydration side products. This necessitates a delicate balance of active sites on the surface and comprehensive understanding of the contribution each site makes to the reaction energetics in order to maximize butadiene productivity. In this presentation we showcase our recent research efforts in this area and report on identification of structure-activity relationships using complimentary theoretical and spectroscopic characterization, as well as evaluation of catalyst stability under relevant process conditions. Atomistic modeling for DFT calculations, coupled with experimental validation, has shown that increasing Ag dispersion on the surface helps to mitigate the formation of unwanted dehydration side product. Alternative synthesis methods involving the dispersion of Zr and incorporation into the framework of SiO2 indicate that the type of Lewis acidity plays a role in overall activity. Catalyst lifetime studies were performed in order to investigate the effects of Na doping, H2O co-feed with ethanol, and operating with H2 co-feed on overall catalyst activity and stability. Ultimately, characterization of structure-activity relationships and optimization of process conditions to increase yield and stability will allow for the design of more cost-effective, industrially significant systems for producing renewable butadiene in the future.

Identification of Structure-Activity Relationships and Optimization of the Ag-ZrO2/SiO2 Catalyst System for the Single-Step Conversion of Ethanol to Butadiene

ACS Fall 2020 Virtual Meeting

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