Open AccessSurface Selective 1H and 27Al MAS NMR Observations of Strontium Oxide Doped γ-Alumina
Author(s) -
Nathan S. Barrow,
Andrew Scullard,
Nicola Collis
Publication year - 2016
Publication title -
johnson matthey technology review
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.571
H-Index - 49
ISSN - 2056-5135
DOI - 10.1595/205651316x690943
Subject(s) - catalysis , magic angle spinning , strontium , oxide , magic angle , chemistry , nmr spectra database , doping , inorganic chemistry , analytical chemistry (journal) , crystallography , materials science , nuclear magnetic resonance spectroscopy , stereochemistry , spectral line , organic chemistry , optoelectronics , physics , astronomy
High-surface area γ-alumina is industrially used as a catalyst support. Catalytically active elements are doped onto the support, where they can bind to AlO 4 , AlO 5 or AlO 6 sites on the surface. Pretreating the surface with alkaline earth oxides can alter the availability of these surface sites, hence affecting the catalytic activity. The surface binding sites of strontium oxide (SrO) on γ-alumina were previously unknown. Direct 27 Al magic angle spinning nuclear magnetic resonance (MAS NMR) could not detect AlO 5 sites at 9.4 T, so 1 H‐ 27 Al cross-polarisation (CP) MAS NMR was used to preferentially select the surface environment signals. We directly observed the three surface environments on dehydrated γ-alumina as a function of SrO impregnation up to 4 wt% SrO. We found that Sr 2+ preferentially binds to AlO 5 and AlO 6 surface sites. 1 H MAS NMR revealed SrO impregnation causes a reduction in the terminal (−0.3 ppm) and bridging (2.2 ppm) hydroxyl environments, as well as the promotion of a new peak in between these sites, at 0.5 ppm. By using 1 H‐ 27 Al CP/MAS NMR the relative proportions of surface sites on γ-alumina can be determined, allowing an optimal level of SrO doping that can saturate all the AlO 5 sites. Importantly, this provides a method of subsequently depositing catalytically active elements on just the AlO 4 or AlO 6 sites, which can provide a different catalytic activity or stability compared to the AlO 5 binding site.