Structural changes occurring upon dehydration of zeolite rho. A study using neutron powder diffraction and distance-least-squares structural modeling

Crystalline powder samples of zeolite Rho have been studied by means of the Rietveld refinement technique applied to neutron powder diffraction data. Upon dehydration, the structure changes from centric (Im3m, a = 15.03 Å) to acentric (I43m, a = 14.69 Å). The structural change is accompanied by an elliptical distortion of the double 8-ring pore openings. The magnitude of this distortion has been measured under a variety of conditions of temperature and absorbant loading and compared to that predicted from distance-least-squares (DLS) structure-modeling techniques. There is good agreement between predicted and observed structures. In addition, DLS has allowed a rationalization of the observed symmetry of Rho and its rapid transition from the centric to the acentric form.