(476d) Ethanol Upgrading to Olefins over Metal-Containing Beta Zeolites: Characterization and Catalysis | AIChE

(476d) Ethanol Upgrading to Olefins over Metal-Containing Beta Zeolites: Characterization and Catalysis


Borate, S. - Presenter, The University of Alabama
Harris, J. W., University of Alabama
Liu, D., University of Maryland
Sutton, A. D., Oak Ridge National Laboratory
Li, Z., Zhenglong Li
Purdy, S., Oak Ridge National Laboratory
Wegener, E. C., Argonne National Laboratory
Zhang, J., Oak Ridge National Laboratory
We report the selective conversion of ethanol to butene-rich olefins over metal-containing (i.e., Cu, Zn, and Y) dealuminated Beta (deAlBeta) zeolite catalysts. CuZnY/deAlBeta was prepared by physically mixing metal salts with deAlBeta or by incipient wetness impregnation, followed by heating under flowing air (823 K). Catalysts were characterized by X-ray diffraction, nitrogen physisorption, X-ray adsorption spectroscopy, scanning transmission electron microscopy, and probe molecule chemisorption followed by collection of transmission FTIR spectra. Each metal plays a distinct role in the multistep pathway from ethanol to olefins. Ethanol dehydrogenation to acetaldehyde occurs on both Cu and Zn, followed by aldol condensation of acetaldehyde to form crotonaldehyde. With increasing Y weight loading (0-7 wt%), the C-C coupling rate increased from 0.3 to 7 x 10-6 mol gcat-1s-1 (<10% conversion, 543 K). FTIR analyses revealed that each metal binds pyridine as a Lewis acid site (LAS), and that the various LAS can be distinguished by the vibrational frequency of adsorbed pyridine. The amount of pyridine adsorbed to Lewis acidic Y sites (YLAS) increased linearly with increasing Y loading and in direct proportion to the C-C coupling rate, suggesting that YLAS are the predominant active sites for C-C coupling in CuZnY/deAlBeta. Titration with pyridine under static vacuum was used to quantify the integrated molar extinction coefficient for pyridine bound to YLAS, and to quantify the number of moles of YLAS by saturating Y/deAlBeta samples with pyridine. In situ pyridine titrations during conversion of ethanol and acetaldehyde to butadiene (503 K) were used to estimate the number of Lewis acidic active sites present during reaction, and these estimates agreed within experimental error to the number of YLAS quantified by pyridine FTIR (463 K). Thus, we propose that quantification of YLAS via ex situ pyridine FTIR reliably quantifies active sites for butadiene formation over Y/deAlBeta.