Effect of Heating on Palygorskite and Acid Treated Palygorskite Properties

The behavior of palygorskite as an adsorbent or catalyst support is governed mainly by the magnitude of its surface areas and degree of surface activity. Most heterogeneous catalytic reactions take place at elevated temperatures. It is important and necessary to known the possible changes in the physicochemical properties and hence the catalytic activity due to the thermal treatment. The present work investigates the effect of heat treatment on the surface and textural properties of palygorskite and acid activated palygorskite. Samples were heated at the required temperatures (150 degrees C, 350 degrees C, 550 degrees C and 750 degrees C) for four hours. The chemical analysis, X-ray diffraction, thermal analysis, and textural properties evaluated on the basis of the nitrogen adsorption have been reported for different samples. Acid-treated samples showed a shift of the DTA curves maxima to low temperatures with increasing acid treating time. The weight loss observed between 300-900 degrees C was approximately half of the value observed for the untreated mineral over the same temperature range. On heating, water molecules are removed causing changes in the BET surface area and the porosity. The modification as a function of the temperature differs with the samples. However, at 750 degrees C, a noticeable decrease of the surface area, which is attributed to closure of the mesoporosity, was observed for all the samples.