Random Distribution of EFG Parameters in 27Al MAS NMR Spectra of AlO x /SiO2 Catalysts and Related Systems

Abstract

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.