A synchrotron X-ray powder diffraction study of highly crystalline low-silica zeolite P during Na-Ca ion exchange

The structure of a highly crystalline sample of low-silica zeolite NaP has been investigated after having been partly ion-exchanged against calcium. A t intermediate compositions, the synchrotron X-ray powder diffraction patte rn of Na1-xCaxP (x = 0.7) shows the coexistence of two immiscible phases: a sodium-rich and calcium-rich variety of zeolite P. The structures of these phases, which have been refined by the Rietveld method, are very similar t o those described previously for the end-members. The miscibility gap is es timated to extend from x=0.16 to x=1.0, in reasonable agreement with previo us findings from ion-exchange selectivity plots. (C) 2000 Elsevier Science B.V. All rights reserved.