Infrared Studies of Surface Acidity and Reversible Folding in Palygorskite

C. Blanco1, J. Herrero1, S. Mendioroz2 and J. A. Pajares2
1 Departamento de Química, Universidad de Cantabria 39005 Santander, Spain
2 Instituto de Catálisis y Petroleoquímica, CSIC Serrano, 119, 28006 Madrid, Spain

Abstract: The infrared absorption spectra of a palygorskite sample from Cáceres, Spain, showed two previously unreported bands in the OH-stretching region at 3420–3440 and 3220–3230 cm−1 after evacuation at 90°–23°C. These bands, which reached maximum intensity after the sample was heated at 150°C, were assigned to OH in the H : Si-O-Si and H : Si-O-Al groups, respectively. To characterize the nature of these OH groups, pyridine was adsorbed on the sample. The resultant spectra suggest that at 150°C the palygorskite folded and OH groups protonated, resulting in the formation of a deformed pyridinium ion between 150° and 290°C. A high concentration of thermally stable Lewis-acid sites on the surface of the palygorskite was also noted.

Key Words: Infrared spectroscopy • Lewis-acid sites • Palygorskite • Protonation • Pyridine

Clays and Clay Minerals; August 1988 v. 36; no. 4; p. 364-368; DOI: 10.1346/CCMN.1988.0360412
© 1988, The Clay Minerals Society
Clay Minerals Society (www.clays.org)