Thermally activated Palygorskite (Pg) has been found to be a good adsorbent material for ammonia (NH3) and sulfur dioxide (SO2). This research investigated the effect of thermal treatment on pore structure and surface acid-alkali properties of Pg through the adsorption-desorption of NH3 and SO2. The results showed that, up to 200 degrees C, the adsorption of NH3 on Pg was significantly higher than SO2. This was due to NH3 being adsorbed in the internal surface of Pg and forming hydrogen bonds (H-bonds) with coordinated water. The increase in thermal treatment temperature from 150 to 550 degrees C, showed a gradual decrease in the number of surface acid sites, while the number of surface alkaline sites increased from 200 to 400 degrees C. The change of surface acidity-alkaline sites is due to the collapse of internal channels of Pg and desorption of different types of hydroxyls associated with the Pg structure. Crown Copyright (C) 2010 Published by Elsevier B.V. All rights reserved.