Random Distribution of EFG Parameters in 27Al MAS NMR Spectra of AlOx/SiO2 Catalysts and Related Systems
27Al magic angle spinning (MAS) nuclear amgnetic resonance (NMR) spectroscopy is one of the primary tools in the structural characterization of a variety of alumina-based catalysts. However, the controversy still exists on the proper interpretation of 27Al NMR spectra due to difficulties associated with distribution of NMR parameters and by the experimental limitations. In this work, we present analysis of the 27Al MAS NMR spectra containing signals from Al(4), Al(5) and Al(6) species on the surface of AlOx/SiO2 catalysts and demonstrate several characteristic tell-tale properties of these signals caused by the random distribution of the EFG tensor parameters and by the partial excitation of NMR spectra.
Russian authors gratefully acknowledge the Russian Science Foundation (RSF Grant 14-23-00037) for the financial support. Dr. Z. Gan (NHMF, Florida) is thanked for his help with MQMAS experiments. Prof. I. Wachs is thanked for supplying the samples. Access to the 21.1 T NMR spectrometer was provided by the National Ultrahigh-Field NMR Facility for Solids (Ottawa, Canada), a national research facility funded by a consortium of Canadian Universities, supported by the National Research Council Canada and Bruker BioSpin, and managed by the University of Ottawa (http://nmr900.ca).
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