Acidic properties of synthetic saponites studied by pyridine IR and TPD[ndash ]TG of n-propylamine
(Note: The full text of this document is currently only available in the PDF Version )
Bob R. G. Leliveld, Meike J. H. V. Kerkhoffs, Fred A. Broersma, Jos A. J. van Dillen, John W. Geus and Diek C. Koningsberger
Abstract
The acidity of synthetic Zn and Mg saponites exchanged with H+, Al3+, Na+ and K+ has been studied using DRIFTS of adsorbed pyridine and TPD–TG measurements of adsorbed n-propylamine. The characterisation with IR of adsorbed pyridine revealed the presence of a large amount of Lewis acid sites owing to coordinatively unsaturated metal atoms at the edges of the clay platelets. Hardly any Brönsted sites were observed. However, with TPD–TG measurements of n-propylamine it was possible to quantify the number of Brönsted acid sites. In the H+ exchanged clays with high Si/Al ratios the amine/Al molar ratio was found to be near unity. At lower Si/Al ratios the number of acid sites increased non-linearly with the Al content. This study demonstrates that pyridine is a useful probe for determining Lewis acidity. However, to study the Brönsted acidity of H+ exchanged synthetic saponites, reliable quantitative information can only be obtained using n-propylamine.