The reaction of 2-chloroethylethyl sulfide (CEES) with a high-area Al2O3 surface was investigated. Two
different reactive sites were created by thermally pretreating the Al2O3 powder: isolated hydroxyl sites
and Lewis acid−base pair sites. The reaction of CEES with the isolated hydroxyl groups at 303 and 473
K produced a surface-bound species, which is characterized by a carbon−oxygen stretching mode near
1100 cm-1. This assignment was confirmed by isotopic substitution of 18O into the isolated hydroxyl groups
prior to reaction with CEES. The other reaction product detected at 473 K was HCl. For a more highly
dehydroxylated Al2O3 surface, the reaction of CEES with the Lewis acid−base pairs produced a surface−bound species also exhibiting a carbon−oxygen stretching mode near 1100 cm-1. This species is postulated
to form at O2- Lewis base sites as Al3+−Cl- bonds form on adjacent Lewis acid sites. The adsorption of
pyridine onto the Lewis acid sites prior to CEES exposure effectively closes this reaction pathway. A
maximum Al2O3 reactivity was achieved by pretreatment of the Al2O3 in the temperature range 673−773
K, judging by the integrated absorbance intensity of the product1100 cm-1 mode. This reactivity maximum
is expected if both the isolated hydroxyl groups and Lewis acid−base pairs are involved in the reaction.
The study of adsorption on opaque powdered materials using transmission IR spectroscopy is described. The method involves diluting the optically dense adsorbent powder in solid KBr and then pressing the mixture into a tungsten grid. These thousands of tiny self-supporting samples make intimate contact with the grid array, allowing efficient thermal control of the sample temperature from 100 K upward. It has been found that gas adsorption may be studied on such samples by diffusion of the gas through the KBr matrix to the adsorption sites on the powder sample. Examples of the adsorption of small molecules, CO and CO2, on carbon surfaces and larger molecules, dimethylmethyl phosphonate and 2-chloroethylethyl sulfide, on a resin and an Al2O3 surface, respectively, are given, where KBr dilution opens up spectral regions that are not accessible in pure samples of the adsorbent. Interactional effects between the KBr support and the OH groups on Al2O3 are observed. A unique six-sample method for comparison of the adsorbent/KBr and pure KBr samples under identical conditions of gas pressure and temperature is described.
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