STUDIES OF SURFACE-ACIDITY AND BASICITY O F THE ATTAPULGITE

Attapulgite with the composition of [MgAlFe](5)Si8O20(OH)(2)(OH2)(44)H 2O has been widely used as catalyst or catalyst support in various cat alytic reactions. The surface acidity and basicity of attapulgite shou ld play an important role, in particular, in the acid/base catalyzed r eactions. In this paper, a Tian-Calvet type microcalorimeter was used to measure quantitatively the number and strength of acid/base sites o n the surface of attapulgite sample. The acid/base properties of the s ample were also investigated with infrared spectroscopy and test react ion of isopropanol dehydration. The results indicated that the attapul gite displayed the acidity with initial differential NH3 adsorption he at of 130 kJ/mol and saturated NH3 coverge of 1.5 mu mol/m(2). The str ength distributions of surface acid sites on attapulgite and the calor ometric results suggested that the attapulgite possessed only a few (< 0.1 mu mol/ m(2)) very weak base sites with CO2 adsorption heat lower than 5 kJ/mol. The infrared spectroscopy revealed that the attapulgit e had both Bronsted and Lewis acid sites. Moreover, the Lewis acid sit es (1619 cm(-1)) were stronger than 90 kJ/mol characteric of the NH3 a dsorption heat. In summary, the attapulgite was a weak solid acid with out any basicity compared to the gamma-Al2O3.