Structure of SiO[sub 2] on Al[sub 2]O[sub 3] monolayer catalysts: Investigation by infrared spectroscopy and [sup 29]Si MAS NMR

Journal Article · Fri Jul 01 00:00:00 EDT 1994 · Journal of Catalysis; (United States)

DOI:https://doi.org/10.1006/jcat.1994.1215· OSTI ID:6859491

Sheng, T C ^[1]; Lang, S; Morrow, B A ^[2]; Gay, I D ^[3]

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1. Shandong Univ. (China)
2. Univ. of Ottawa, Ontario (Canada)
3. Simon Fraser Univ., Burnaby, British Columbia (Canada)

Infrared spectroscopy and [sup 29]Si MAS NMR are used to probe the structure of SiO[sub 2] on Al[sub 2]O[sub 3] catalysts prepared by chemical vapor deposition of Si(OCH[sub 3])[sub 4][center dot]SiO[sub 2] loadings from about 0.2-2.5 statistical monolayers are studied. Infrared shows a gradual disappearance of AlOH vibrations as the SiO[sub 2] loading is increased. A population of inaccessible AlOH is also observed. The Si-O-X asymmetric stretching frequency shows a continuous variation with SiO[sub 2] content, consistent with X varying from Al at low levels to Si at high levels of silica. [sup 29]Si NMR shows composite peaks at all SiO[sub 2] levels. At the lowest level most intensity is concentrated in the -80 to -85 ppm range, corresponding to Si with attached -OAl groups. At the highest silica levels, the spectrum can be deconvoluted into peaks at -108, -100, and -92 ppm. These correspond to Si(OSi)[sub 4], Si(OSi)[sub 3]OH, and mixtures of Si(OSi)[sub 2](OH)[sub 2] with -OAl-containing species. A model is proposed for build up of the silica layer on these catalysts. Random deposition of silica on any available surface is shown to give a semiquantitative account of the experimental results. 31 refs., 6 fig., 2 tabs.

• OSTI ID: 6859491
• Journal Information: Journal of Catalysis; (United States), Journal Name: Journal of Catalysis; (United States) Vol. 148:1; ISSN 0021-9517; ISSN JCTLA5
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ABSORPTION SPECTROSCOPY
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
CATALYSTS
CHALCOGENIDES
MAGNETIC RESONANCE
MINERALS
NUCLEAR MAGNETIC RESONANCE
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
RESONANCE
SILICA
SILICON COMPOUNDS
SILICON OXIDES
SPECTROSCOPY
STRUCTURAL CHEMICAL ANALYSIS