| Abstract |
Thermal and hydrothermal stability of SAPO-40 were studied by X-ray powder diffraction (XRD) and magic-angle spinning nuclear magnetic resonance (MAS-NMR). For the X-ray study, the hydrothermal treatments were carried out, in situ, in a high-temperature chamber. The SAPO-40 structure shows a remarkable stability to high temperatures under both dry and humid air. At high temperatures a reorganisation of silicon occurs, but the long-range order is only lost above ca. 1000 degrees C. Changes in the XRD pattern induced by water at room temperature are completely reversible upon re-heating at 200 degrees C, as well as the changes in the coordination and local environments of aluminium and phosphorus observed by NMR. For silicon however, some changes, that are observed upon hydration, remain after dehydration. |
