Hydrothermal damage of ion-exchanged A-type zeolite cation-directed mechanisms of phase transformation

Zeolite-4A is a hydrated aluminosilicate which becomes more hydrated when exchanged with transition metals. In this work, the dehydration kinetics of cobalt, nickel and copper(II)-exchanged zeolite-4A were studied by means of TG and DTA over the temperature range from 20 to 500°C, and the numbers of water molecules in the metal-exchanged zeolite samples were calculated. It was observed that, as the ionic radius of the hydrated metal increased, the number of water molecules also increased. The loss of water from the zeolite samples generally occurred in the temperature range 100–300°C and was manifested in the DTA graphs by an extended endothermic effect. The DTA curves demonstrated that the peak position shifted towards lower temperatures as the metal concentration increased or, in other words, the water of hydration increased. The kinetic parameters (order of reaction and activation energy) were calculated via the Coats and Redfern method. The process of dehydration was found to follow first-order kinetics.

TG and DTA Study of the Thermal Dehydration of Metal-exchanged Zeolite-4A Samples

M. Judanne Wilson

Papers

Thermal analysis of synthetic zeolites of the a series (part I)

Thermal analysis of synthetic zeolites of the a series: Part II. Zeolites containing nickel and cobalt ions