(532f) Thermochemical Modulation on Boron-, Phosphorus-, and Sulfur-Containing Siliceous Zeolites for Renewable Tetrahydrofuran Dehydra-Decyclization to Butadiene

Renewable 1,3-butadiene (BD, C4H6) can be synthesized from the tandem decyclization and dehydration of biomass-derived tetrahydrofuran (THF) on attenuated solid acid zeolite catalysts. BD is a highly solicited monomer deployed in the synthesis of functional polymers, including cis-1,4- polybutadiene and styrene-butadiene rubber (SBR), primary constituents of tires. Recent findings accent the selective conversion of THF to BD on phosphorus-modified siliceous zeolites (P-zeosils) at both, high and low space velocities (catalyst contact time). Noticeably, the efficient production of BD platform chemical requires a profound understanding of the paired-interaction effect of the process variables and conditions on the catalyst activity, selectivity and stability. Correspondingly, probing the effect of water generated during the chemo-catalytic conversion or intrinsic to biomass-derived feedstocks on the catalyst framework and performance is pivotal to the optimization and scale-up of these systems. We have performed a Box-Behnken surface analysis to comprehend and enhance the selective conversion of THF to BD on the Brønsted acid sites (BAS) of Boron (B)-, Phosphorus (P)-, and Sulfur (S)-containing silicalite-1 catalysts at various process conditions; namely, temperature (200-370°C), weight hourly space velocity (1.9-19.1h^-1), and water content in the feed stream (0-10 %). Detailed kinetic measurements revealed that all three catalysts exhibit competitive selectivity to BD ca. 30-99% in the order of P-MFI > S-MFI > B-MFI at both low (0%) and high (10%) water content for conversions 4%. Markedly, initial P-MFI and S-MFI exposure to water vapor augments BD site time yields (STYs), which subsequently subsided as evinced by a steepened deactivation profile in a 5-hour time-on-stream analysis. This phenomenon coincides with active site evolution in the presence of water vapor as related to BAS density (e.g., hydrolysis of P-O-P linkages). Overall, this study progresses the ability to control reaction pathways and product selectivity, a headway towards dehydra-decyclization chemistry optimization on microporous zeolites.