An in situ XAS study on the incorporation of metal ions into AlPO4-5 framework in hydrothermal synthesis process

摘要

The in situ X-ray Absorption Spectroscopy (XAS) was employed to probe the incorporation of transition metal ions, such as Mn2+, Fe3+, Co2+ and Ni2+, from precursor gel to AlPO4-5 framework in hydrothermal synthesis process. With the crystallization, the number of coordinated oxygen around metal ions changes from 6 to 4, associated with a decrease in the coordination distance of metal ions to oxygen, as revealed by XAS. However, these metal ions are different in the incorporation behaviour and mechanism. The transition of Co2+ into the tetrahedral framework of AlPO4-5 is completed at 150 oC with the emergence of longrange ordered microporous structure, while the incorporation of Mn2+ and Fe3+ is much more difficult and starts after the build-up of microporous structure. On the other hand, the existence of Si4+ in the precursor gel has also considerable influences on the synthesis process.