title: 17O magic angle spinning NMR studies of Brønsted acid sites in zeolites HY and HZSM-5.
abstract: High-resolution 17O/1H double resonance NMR spectra were obtained for two zeolites, one with a low Si/Al ratio (zeolite HY) and one with a high Si/Al ratio (HZSM-5), to investigate their local structure and Brønsted acidity. Two different oxygen signals, corresponding to Brønsted acid sites in supercages and sodalite cages of zeolite HY were readily resolved in the two-dimensional (2-D) 1H-17O heteronuclear correlation (HETCOR) NMR spectra allowing the 17O isotropic chemical shift (deltaCS) and quadrupolar coupling parameters (quadrupolar coupling constant, QCC, and asymmetry parameter, eta) for the two oxygen atoms to be extracted. Similar experiments for HZSM-5 showed that the sites in this system are associated with a much larger distribution in NMR parameters than found in HY. 17O-1H rotational echo double resonance (REDOR) NMR was applied to probe the O-H distances in zeolites HY and HZSM-5. Weaker 17O-1H dephasing was observed for zeolite HZSM-5 in comparison to that of HY, consistent with longer O-H bonds and/or increased proton mobility.
authors.affiliation: Department of Chemistry, State University of New York at Stony Brook, Stony Brook, New York 11794-3400, USA.
authors.forename: Luming
authors.initials: L
authors.lastname: Peng
authors.forename: Hua
authors.initials: H
authors.lastname: Huo
authors.forename: Yun
authors.initials: Y
authors.lastname: Liu
authors.forename: Clare P
authors.initials: CP
authors.lastname: Grey
mesh_terms: D000143:Acids / Q000737:chemistry*; D000535:Aluminum / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy / Q000379:methods* / Q000592:standards; D008958:Models, Molecular; D010103:Oxygen Isotopes; D012015:Reference Standards; D012680:Sensitivity and Specificity; D012825:Silicon / Q000737:chemistry; D017641:Zeolites / Q000737:chemistry*
chemical_list: D000143:Acids; D010103:Oxygen Isotopes; D017641:Zeolites; D000535:Aluminum; D012825:Silicon