Spectroscopic study of anatase properties. Part 3.—Surface acidity

Abstract

Surface acidity of two preparations of anatase has been investigated by following the adsorption of pyridine (Py), carbon monoxide and linearly held carbon dioxide.

Py chemisorbs with high coverages, yielding a hydrogen-bonded species and two types of coordinated base, whereas the pyridinium ion is only produced in the presence of a fair amount of sulphate contaminants arising from the method of preparation. The most strongly held Py species coordinates to clusters of Lewis-acidic centres and the frequency of the 8a mode is peculiar to three different cluster sizes.

CO chemisorbs with low coverages on the most acidic Lewis centres and reveals the heterogeneity of these centres, not revealed by Py.

Linear CO₂ adsorbs at those sites responsible for CO chemisorption and is sensitive to lateral effects and to the polarity of the surface layer.