Cascade Reaction of Ethanol to Butadiene over Multifunctional Silica-Supported Ag and ZrO2 Catalysts

Although butadiene is currently a by-product of naphtha cracking, interest in producing butadiene from bio-based ethanol has increased because of the lower environmental impact of the ethanol to butadiene reaction. Furthermore, this work explores a multifunctional catalyst system composed of silica-supported Ag and ZrO₂ used for the cascade reaction of ethanol to butadiene at 573 K. The Ag and ZrO₂ components were synthesized on separate support particles enabling characterization of each component without interference from the other. High selectivity to butadiene (65%) at high ethanol conversion (75%) was achieved with an appropriate ratio of Ag and ZrO₂ in the reactor. Silver catalyzed the initial dehydrogenation of ethanol to acetaldehyde while ZrO₂ catalyzed the C-C coupling and subsequent dehydration reactions. The silica-supported ZrO₂ exhibited superior selectivity relative to bulk ZrO₂ in the Ag-promoted ethanol to butadiene reaction. Results from Zr K-edge X-ray absorption spectroscopy and UV-Vis spectroscopy showed that ZrO₂ was highly dispersed on the silica support over a range of loadings. Infrared spectroscopy of adsorbed pyridine, CO, and CO₂, and kinetics of probe reactions 1-butene double bond isomerization, 2-propanol decomposition, and ethanol hydrogenation of acetone were used to compare the acid-base nature and chemical reactivity of silica-supported ZrO₂ to bulk ZrO₂.