Spectroscopic study of anatase properties. Part 3. Surface acidity

The surface acidity of 2 prepns. of anatase was examd. by studying the adsorption of pyridine, CO, and linearly held CO2. Pyridine chemisorbs with high coverages, giving a H-bonded species and 2 types of coordinated base, whereas pyridinium is produced in the presence of a fair amt. of SO42- contaminants arising from the method of prepn. The most strongly held pyridine species coordinates to clusters of Lewis-acidic centers and the frequency of the 8a mode is peculiar to 3 different cluster sizes. CO chemisorbs with low coverages on the most acidic Lewis centers and shows the heterogeneity of these centers. Linear CO2 adsorbs at the sites responsible for CO chemisorption and is sensitive to lateral effects and to polarity of the surface layer