Infra-red studies of reactions on oxide surfaces. Part 1.—Boron trifluoride on silica

Abstract

Infra-red spectroscopy has been used to study the adsorption of boron trifluoride on silica. On highly dehydroxylated samples chemisorption is rapid and the major product initially appears to be a surface SiOBFz species. This species is also formed when BF3 interacts wtih totally dehydroxylated silicas which have been prepared by heating silica in vacuum at about 1250°C. Spectroscopic evidence indicates that on highly or totally dehydroxylated silica, BF3 preferably reacts with a new reactive site, probably a siloxane bridge site, which is formed as a result of the removal of the surface silanol groups during heating. Only after the reaction is complete on the " siloxane " sites does chemisorption take place with silancjl groups if these are present. During prolonged evacuation the surface SiOBFz groups react further with trace amounts of water to produce (Si0)2BF groups; the latter are also produced during the initial stages of chemisorption when the silanol concentration is high. When water or air is admitted after chemisorption of BF3, a spectrum characteristic of boric acid is observed.

Sodium diffusion through amorphous silica surfaces: A molecular dynamics study

“…A ring is a particularly interesting structure because it can be detected using infrared and Raman spectroscopy. In particular the highly strained twofold rings result in infrared-active stretching modes 41,47 at 888 and 908 cm −1 . In order to determine the probability P n for a given Si atom, whose coordinate along the normal direction to the surface is in one of the three regions, to be a member of a n-fold ring we have used the algorithm described in 48 .…”

Transmission Infrared Spectroscopy for High Surface Area Oxides

“…This precluded observation of the region where many bending modes would be expected and prevented complete assignment of surface structures. After much experience it is now possible to prepare very thin, high quality discs of Cabosil and other oxides (10 mg/cm 2 ) and the resultant increase in available information is illustrated by the work of Morrow and his co-workers on Cabosil (11)(12)(13)(14). Thus, Morrow and Cody were able to obtain the spectra shown in Fig.…”

Infrared Spectroscopic Analyses of Transformations of Chemical Species on the Silica Highly-Reacted with Gaseous BF 3

“…6 Besides these two species, the presence of a species called "C" was proposed though its characteristics was not known. 6 A series of studies to investigate the transformations of the BFn species on the silica were performed through analyses of infrared spectra measured under extensive conditions of experiments. In the preceding paper, 7 the constituent bands, including new ones due to the species C, of the spectra of the silica reacted with gaseous BF3 were all clarified in positions and in assignments.…”

“…[3][4][5] Infrared spectra of BFn (n = 1, 2) species, which were formed on the silica under the condition of relatively low pressure of BF3 added such as 0.1 Torr, were measured, and transformations of the BFn species on such a sparsely-reacted silica were discussed. 1,6,7 When BF3 with low pressure reacts with the silica, a chemical species "A" containing -BF2 is first produced on the silica, and it is transformed to a species "B" containing >BF by an irreversible reaction with its neighboring OH group. 6 Besides these two species, the presence of a species called "C" was proposed though its characteristics was not known.…”

“…1,6,7 When BF3 with low pressure reacts with the silica, a chemical species "A" containing -BF2 is first produced on the silica, and it is transformed to a species "B" containing >BF by an irreversible reaction with its neighboring OH group. 6 Besides these two species, the presence of a species called "C" was proposed though its characteristics was not known. 6 A series of studies to investigate the transformations of the BFn species on the silica were performed through analyses of infrared spectra measured under extensive conditions of experiments.…”