Active sites on SiO{sub 2}. Role in CH{sub 3}OH decomposition

Journal Article · Sat Jul 01 04:00:00 EDT 1995 · Langmuir

DOI:https://doi.org/10.1021/la00007a044· OSTI ID:91253

Wovchko, E A; Camp, J C; Glass, J A; Yates, Jr, J T ^[1]

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1. Univ. of Pittsburgh, PA (United States)

The dehydroxylation of SiO{sub 2} and adsorption and thermal decomposition of CH{sub 3}OH on dehydroxylated SiO{sub 2} prepared at extreme temperatures up to 1475 K has been studied using transmission infrared spectroscopy. Formation of Si-O Si linkages (as evidenced by 888 and 908 cm{sup -1} bands) is directly related to the loss of the isolated SiO-H band at 3748 cm{sup -1} during SiO{sub 2} dehydroxylation to produce H{sub 2}O{sub 1}. High-resolution (0.75 cm{sup -1}) studies of the isolated SiO-H band show sharpening and a slight 4 cm{sup -1} shift to higher frequency with decreasing -OH coverage and may be explained by site inhomogeneity effects. Adsorption of CH{sub 3}OH on dehydroxylated SiO{sub 2} occurs first by reaction with SiOSi sites, followed by exchange with SiOH groups at elevated temperatures leading to SiOCH{sub 3} surfaces species. CH{sub 3}{sup 18}OH adsorption studies demonstrated that adsorption on SiOSi sites occurs by cleavage of the methanol O-H bond forming SiOH and Si{sup 18}OCH{sub 3}. Thermal decomposition of SiOCH{sub 3} groups creates SiH{sub x} (x = 1,2) species and prevents formation of the SiOSi sites indicative of the production of free radical sites at the surface. At temperatures above 1300 K, SiH{sub x} decomposition leads to SiOSi site formation. 40 refs., 11 figs.

• Sponsoring Organization: USDOE
• OSTI ID: 91253
• Journal Information: Langmuir, Journal Name: Langmuir Journal Issue: 7 Vol. 11; ISSN LANGD5; ISSN 0743-7463
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
ADSORPTION
DECOMPOSITION
HYDROXYL RADICALS
HYDROXYLATION
INFRARED SPECTRA
METHANOL
SILICA
TEMPERATURE RANGE 1000-4000 K