Compressibility of microporous materials with CHA topology: 1. Natural chabazite and SAPO-34

Abstract

The H P behaviors of a natural chabazite and of SAPO-34 as-synthesized were investigated by means of in situ synchrotron X-ray powder diffraction, with the aim of understanding the role of the framework/extraframework content on the response to pressure. Compressibility was determined with silicon oil, as non-penetrating P-transmitting medium, up to 7.6 GPa and 4.5 GPa for chabazite and SAPO-34, respectively. The isothermal Equation of States (EoS), refined with a second-order Birch–Murnagan EoS, yielded the following parameters: V 0 = 842(2) Å 3, K 0 = 35(5) GPa for chabazite at P ⩽ 1 GPa, V 0 = 831(1) Å 3, K 0 = 62(1) GPa for chabazite at P ⩾ 1.4 GPa, and V 0 = 2439(4) Å 3, K 0 = 29(1) GPa, for SAPO-34. These results indicate that chabazite is definitely less compressible than SAPO-34. This is mainly ascribed to the more complex and hindering extraframework content of the natural sample. No complete structural refinements of the powder patterns were performed, but the compressibility of these materials with CHA topology was tentatively interpreted on the basis of the deformation mechanism observed in the structurally related zeolite levyne. The comparison between the volume decrease induced on chabazite by high pressure and by high temperature indicates that this zeolite is much more flexible under compression than upon dehydration.