Observation of a rhombohedral phase change during the dehydration of zinc-exchanged zeolite A

Temperature dependent powder X-ray diffraction studies of zinc-exchanged zeolite A (LTA structure type; cubic at room temperature) have demonstrated the presence of a non-cubic phase between 150 °C and 600 °C. Analysis of the data indicated that a rhombohedral phase was formed with refined lattice parameters a = 17.182(3) Å and α = 59.147(9)° (after quenching from 150 °C to room temperature under vacuum). Heating above 600 °C produced a second cubic phase, which persisted upon cooling, and the rhombohedral phase only appeared for samples that had not been heated above 600 °C. The distortion from cubic symmetry may be linked to the formation of species such as Znx(H2O)ym+ or Znx(H2O)y(OH)zn+ during dehydration.