TPD (ammonia) in Micromeritics 2900 TPD equipment. The acid treated kaolin clay samples were out gassed under He flow (50 N ml/min) by heating with a rate of 15 C/min up to 650 C and remaining at this temperature for 30 min. After cooling to 180 C, the samples were treated with a 30 N ml/min ammonia flow for 30 min