Cascade Reaction of Ethanol to Butadiene over Ag-Promoted, Silica- or Zeolite-Supported Ta, Y, Pr, or La Oxide Catalysts
Konstantin Mamedov, Robert J. Davis
Abstract
Ethanol converts to 1,3-butadiene in the presence of suitable multifunctional catalysts. In this work, Lewis acid cations Ta, Y, Pr, and La were dispersed on amorphous silica or β zeolite, and after physically mixing with silica-supported Ag nanoparticles, were tested in the cascade reaction of ethanol to butadiene at 573 K. The Lewis acid catalysts were characterized by X-ray fluorescence, N 2 physisorption, scanning transmission electron microscopy (STEM), X-ray diffraction, and diffuse reflectance (DR) UV–vis and X-ray photoelectron spectroscopies. High-resolution STEM images confirmed the small oxide cluster size on the silica support. Results from DR UV–vis spectroscopy showed that zeolite-supported Ta and Pr catalysts had a smaller metal oxide cluster size, relative to their SiO 2 counterparts. X-ray photoelectron spectroscopy confirmed that the oxidation state of the cations supported on the zeolite remained the same as that of their SiO 2 -supported analogues. The selectivity of the C 4 coupling products toward butadiene relative to butanol correlated with the acid strength of the Lewis acid cations, as evaluated by the 2-propanol decomposition reaction to propene and acetone, with Ta being the most selective. The rate of C–C coupling over the zeolite-supported cations was enhanced by an order of magnitude compared to those cations supported on amorphous SiO 2 .