Heats of immersion in relation to water losses of cobalt- and nickel-exchanged mordenites

Abstract

Cobalt- and nickel-exchanged mordenites were prepared from synthetic sodium mordenite by cation-exchange technique. The samples were thermally dehydrated in vacuo in the temperature range 100–480°C. The effects of thermal treatment on water losses and heats of immersion in water are discussed. For both mordenites, the integral heats of immersion change in similar fashion, with some limited variation in values of the water loss and heat of immersion. Cobalt-exchanged mordenite samples show greater water losses and consequently have higher immersional heats. Based on the changes of the heat of immersion per molecule, the occurrence of some specific interactions in the system water + sample NiNa-M at low dehydration temperature (100°C) is evident. At higher dehydration temperatures, the two mordenite samples were significantly comparable in the rates of water loss, and consequently less significant changes in average heats of immersion were observed. This is taken as evidence for some reversible dehydration/hydration phenomena at high-temperature treatments.