sup 27 Al cross polarization of aluminas. The NMR spectroscopy of surface aluminum atoms

Journal Article · Wed Aug 02 04:00:00 EDT 1989 · Journal of the American Chemical Society; (USA)

DOI:https://doi.org/10.1021/ja00198a012· OSTI ID:7157864

Morris, H D; Ellis, P D ^[1]

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1. Univ. of South Carolina, Columbia (USA)

The selective cross polarization of surface aluminum atoms is demonstrated and applied to {gamma}- and {alpha}-aluminas. The relatively high hydration levels of the {gamma}-alumina surface (out of the bottle) allow the observance of two surface species. Upon dehydration only one, somewhat broader resonance, with lower signal-to-noise ratio, can be resolved. Upon extensive dehydration this signal disappears. By comparison to Boehmite and {alpha}-alumina, these resonances are assigned to surface octahedral sites (3.0 ppm) and tetrahedral sites ({approximately} 62.0 ppm). All chemical shifts are reported relative to Al(NO{sub 3}){sub 3} {times} xH{sub 2}O. It is demonstrated that these resonances represent surface Broensted sites, and that they are not contaminated by Lewis acid sites or subsurface species. The Lewis acid sites can be selectively observed by replacing the surface hydroxyl protons with deuterons and adsorbing a Lewis base probe, pyridine, on the surface. In this case the {sup 1}H on the pyridine provide the polarization for the {sup 27}Al resonance. The {alpha}-alumina used in this study appears to have a low number of surface hydroxyls concomitant with its low surface area (5.5 m{sup 2}/g). This is reflected in the low (relative to {gamma}-alumina) {sup 27}Al signal-to-noise ratio obtained with this sample. Overall, this approach appears to be an excellent way to nondestructively characterize these surfaces. More importantly, the success of surface selective cross polarization methodology illustrates that other nuclides are equally amenable to such experiments, and that this approach could be very useful as a general surface chemistry method for characterization of surfaces.

• OSTI ID: 7157864
• Journal Information: Journal of the American Chemical Society; (USA), Journal Name: Journal of the American Chemical Society; (USA) Vol. 111:16; ISSN 0002-7863; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360603* -- Materials-- Properties
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201 -- Chemical & Physicochemical Properties
ALUMINATES
ALUMINIUM COMPOUNDS
CATALYSTS
DATA
DATA ANALYSIS
DEHYDRATION
EXPERIMENTAL DATA
INFORMATION
MAGNETIC RESONANCE
MEASURING INSTRUMENTS
MEASURING METHODS
NUCLEAR MAGNETIC RESONANCE
NUMERICAL DATA
OXYGEN COMPOUNDS
POLARIZATION
RESONANCE
SURFACE PROPERTIES