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Dorn RW, Cendejas MC, Chen K, Hung I, Altvater NR, McDermott WP, Gan Z, Hermans I, Rossini AJ. Structure Determination of Boron-Based Oxidative Dehydrogenation Heterogeneous Catalysts with Ultra-High Field 35.2 T 11B Solid-State NMR Spectroscopy. ACS Catal 2020; 10:13852-13866. [PMID: 34413990 DOI: 10.1021/acscatal.0c03762] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Boron-based heterogenous catalysts, such as hexagonal boron nitride (h-BN) as well as supported boron oxides, are highly selective catalysts for the oxidative dehydrogenation (ODH) of light alkanes to olefins. Previous catalytic measurements and molecular characterization of boron-based catalysts by 11B solid-state NMR spectroscopy and other techniques suggests that oxidized/hydrolyzed boron clusters are the catalytically active sites for ODH. However, 11B solid-state NMR spectroscopy often suffers from limited resolution because boron-11 is an I = 3/2 half-integer quadrupolar nucleus. Here, ultra-high magnetic field (B 0 = 35.2 T) is used to enhance the resolution of 11B solid-state NMR spectra and unambiguously determine the local structure and connectivity of boron species in h-BN nanotubes used as a ODH catalyst (spent h-BNNT), boron substituted MCM-22 zeolite [B-MWW] and silica supported boron oxide [B/SiO2] before and after use as an ODH catalyst. One-dimensional direct excitation 11B NMR spectra recorded at B 0 = 35.2 T are near isotropic in nature, allowing for the easy identification of all boron species. Two-dimensional 1H-11B heteronuclear correlation NMR spectra aid in the identification of boron species with B-OH functionality. Most importantly, 2D 11B dipolar double-quantum single-quantum homonuclear correlation NMR experiments were used to unambiguously probe boron-boron connectivity within all heterogeneous catalysts. These experiments are practically infeasible at lower, more conventional magnetic fields due to a lack of resolution and reduced NMR sensitivity. The detailed molecular structures determined for the amorphous oxidized/hydrolyzed boron layers on these heterogenous catalysts will aid in the future development of next generation ODH catalysts.
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Affiliation(s)
- Rick W. Dorn
- Department of Chemistry, Iowa State University, Ames, Iowa 50011, United States
- Ames Laboratory, US Department of Energy, Ames, Iowa 50011, United States
| | - Melissa C. Cendejas
- Department of Chemistry, University of Wisconsin − Madison, Madison, Wisconsin 53706, United States
| | - Kuizhi Chen
- National High Magnetic Field Laboratory (NHMFL), Tallahassee, Florida 32310, United States
| | - Ivan Hung
- National High Magnetic Field Laboratory (NHMFL), Tallahassee, Florida 32310, United States
| | - Natalie R. Altvater
- Department of Chemical and Biological Engineering, University of Wisconsin − Madison, Madison, Wisconsin 53706, United States
| | - William P. McDermott
- Department of Chemistry, University of Wisconsin − Madison, Madison, Wisconsin 53706, United States
| | - Zhehong Gan
- National High Magnetic Field Laboratory (NHMFL), Tallahassee, Florida 32310, United States
| | - Ive Hermans
- Department of Chemistry, University of Wisconsin − Madison, Madison, Wisconsin 53706, United States
- Department of Chemical and Biological Engineering, University of Wisconsin − Madison, Madison, Wisconsin 53706, United States
| | - Aaron J. Rossini
- Department of Chemistry, Iowa State University, Ames, Iowa 50011, United States
- Ames Laboratory, US Department of Energy, Ames, Iowa 50011, United States
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