Surface acidity of η-alumina. Part 1.—Pyridine chemisorption at room temperature

Abstract

The room temperature adsorption of pyridine on η-Al₂O₃ dehydrated at several temperatures in the 25–700°C range has been studied by i.r. spectroscopy, u.v.-vis reflectance spectroscopy and microgravimetry.

Several species are formed that can be identified on the basis of the spectroscopic features of the 8a ring mode, whereas the 8b mode, which is common to all species, yields the total amount adsorbed. Quantitative interpretation of the spectral data is carried out using a computer program.

The adsorbed species are interpreted as follows: a liquid-like physisorbed species, a species H bonded to surface OH groups through the nitrogen lone pair and three Lewis coordinated species. The latter are assigned to purely octahedral, tetrahedral–octahedral and purely tetrahedral cationic sites, respectively.

The reactions occurring upon Py desorption above 400°C are discussed and a different interpretation is given to that in the literature.