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Identifying Active Sites, Quantifying Site Heterogeneity, and Revealing Site-Site Synergies in Zeolite and Zeotype Catalysts
November 21, 2019 @ 10:00 am - 11:00 am
Zeolite HZSM-5, a member of the MFI family of structures, is an important catalyst from both practical application and fundamental structure-function perspectives. With known uses ranging from cracking, isomerization, and methanol-to-hydrocarbon chemistries, the traditional view of only one type of acidic Brønsted proton site in HZSM-5 has been called into question by recent experimental data on zeolites with relatively high framework Al content. Motivated by surprising increases in reaction rates observed for some hydrocarbon/HZSM-5 probe reactions in the presence of sub-stoichiometric amounts of water, a series of experiments involving catalyst synthesis, selective post-synthetic modifications, cation titrations, and advanced solid-state NMR techniques reveal that multiple Brønsted acid protons can exist in zeolites. The number and type of acid sites can be varied, with significant impacts on reactivity. In addition, crystalline framework Brønsted protons proximate to extra-framework or non-crystalline framework sites are the most reactive species, and when such species are selectively removed, catalyst activity decreases by an order of magnitude or more. Recently acquired data at ultra-high magnetic field strengths of 35.2 Tesla (1.5 GHz) suggest that the highly active sites form at partially-coordinated framework Al atoms, and that positive synergistic effects from water co-addition require their presence. Implications on catalyst synthesis, post-synthetic chemical modifications, thermal history, and responses to phosphorous addition will be discussed.
Dr. Jeffery L. White joined Oklahoma State University in 2005 following a successful period as an Assistant and Associate Professor of Chemistry at North Carolina State University in Raleigh NC. Professor White received his Ph.D. from Texas A&M University in 1992, and has an extensive and varied background in scientific research, including appointments as a postdoctoral fellow with AT&T Bell Laboratories in Murray Hill NJ, a polymer research scientist with Exxon Chemical, and as a group leader in heterogeneous catalysis for methanol-to-olefins chemistry with ExxonMobil. Dr. White has served on the Editorial Advisory Board for the ACS journal Macromolecules, has been honored with a Fulbright Research Fellow, a DuPont Science and Engineering Award, and has had continuous NSF funding as Principal Investigator for 20 years. In addition to NSF, Dr. White’s research in heterogeneous catalysis and materials science is currently funded by ACS PRF, DOE, and several industrial collaborators.
Dr. White has published approximately 80 peer-reviewed journal papers, along with several book chapters and patents, including a composition-of-matter patent detailing for the first time the role of the hydrocarbon pool mechanism in methanol-to-olefin chemistry.