(175c) Active and Selective ZrO2 Based Catalysts for Diene Monomer Production from Biomass.

The production of diene monomers like butadiene and piperylene from biomass resources has recently attracted interest, serving as a sustainable pathway to produce chemical building blocks vital to polymer production. Cyclic ethers like tetrahydrofuran derived from biomass can be converted to butadiene via a dehydra-decyclization chemistry, where Brønsted acidic materials have been demonstrated to be active catalysts. The main challenge is balancing the activity and selectivity of catalysts, where strongly Brønsted acid catalysts are highly active but facilitate undesired reactions (retro-prins condensation, diene oligemerization). Conversely, weakly Brønsted acidic materials are highly selective, but are far less active. Here we demonstrate that Lewis acidic metal oxide catalysts can potentially overcome this challenge, serving as a highly selective and active dehydra-decyclization catalyst. The screening of a variety of metal oxide catalysts shows that ZrO₂ is an effective dehdyra-decyclization catalyst, achieving near quantitative yield to butadiene from THF at 673 K and moderate weight hourly space velocities (1 g THF g cat^-1 hr^-1). The catalyst is highly selective to dienes across a wide range of conditions (> 90%) and is found to be relatively stable with time on stream. Comparing the different phases of ZrO₂ (tetragonal, monoclinic and cubic), we find the catalytic activity of the catalyst is structure insensitive as evidenced by comparable rates and activation energies. Conversely, the stability with time on stream is highly dependent on the phase of ZrO₂, where tetragonal is found to be the most stable. Despite the deactivation, the initial activity of the catalyst can be regenerated through a mild calcination, suggesting a coking mechanism is responsible for the loss in activity.