Thermal transformation of Ba-exchanged A and X zeolites into monoclinic celsian

The thermal transformation of Ba- and (Ba+Li)-exchanged precursors of zeolites A and X into monoclinic celsian has been investigated by X-ray diffractometry, differential thermal analysis, and thermodilatometry. Upon the proper thermal treatment either Ba-exchanged zeolite A or X give rise to the following transformations: zeolite→amorphous phase→hexacelsian→monoclinic celsian. Zeolite A-based precursors are more reactive than zeolite X-based precursors allowing all the reported transformations to occur at far lower temperatures starting from Ba-exchanged zeolite A rather than from Ba-exchanged zeolite X. In particular, starting from zeolite X-based precursors, fully monoclinic celsian may be obtained after 24 h at 1550°C in the absence of Li and after 6 h at 1100°C in the presence of Li, whereas starting from zeolite A-based precursors it may be obtained after 6 h at 1100°C in the absence of Li and by slow heating (1°C/min) up to 900°C in the presence of Li.