Open AccessStructure Determination of Boron-Based Oxidative Dehydrogenation Heterogeneous Catalysts With Ultrahigh Field 35.2 T 11B Solid-State NMR Spectroscopy
Author(s) -
Rick W. Dorn,
Melissa C. Cendejas,
Kuizhi Chen,
Ivan Hung,
Natalie R. Altvater,
William P. McDermott,
Zhehong Gan,
Ive Hermans,
Aaron J. Rossini
Publication year - 2020
Publication title -
acs catalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.898
H-Index - 198
ISSN - 2155-5435
DOI - 10.1021/acscatal.0c03762
Subject(s) - boron , dehydrogenation , solid state nuclear magnetic resonance , nuclear magnetic resonance spectroscopy , nmr spectra database , catalysis , spectroscopy , chemistry , homonuclear molecule , materials science , hexagonal boron nitride , inorganic chemistry , analytical chemistry (journal) , nuclear magnetic resonance , organic chemistry , nanotechnology , spectral line , molecule , physics , quantum mechanics , graphene , astronomy
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 11 B solid-state NMR spectroscopy and other techniques suggests that oxidized/hydrolyzed boron clusters are the catalytically active sites for ODH. However, 11 B 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 11 B 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/SiO 2 ] before and after use as an ODH catalyst. One-dimensional direct excitation 11 B 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 1 H- 11 B heteronuclear correlation NMR spectra aid in the identification of boron species with B-OH functionality. Most importantly, 2D 11 B 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.