Dehydra-Decyclization of Tetrahydrofuran for Butadiene Across the Spectrum of Solid Acidity

Catalytic C-O bond cleavage and dehydration of tetrahydrofuran was evaluated for a set of progressively stronger solid acid catalysts. Strong acids, namely tungsten-based heteropoly acids, exhibited higher activity and selectivity towards butadiene production than more weakly acidic zeolites; enthalpic stabilization in the controlling transition state in butadiene formation contributed to a lower apparent activation energy barrier for stronger acids. The most weakly acidic phosphorus-based zeolite (P self-pillared pentasil, P-SPP) exhibited high selectivity to butadiene (91%). Selectivity to products, mainly butadiene and propene, was controlled by the interplay of enthalpic and entropic contributions to dehydra-decyclization and retro-Prins reactions, respectively. In this balancing act, P-SPP is the least enthalpically stabilized but most entropically favourable in the butadiene formation reaction, resulting in the highly selective formation of butadiene.