Characterization of the amorphous phases formed during the synthesis of microporous material AlPO 4-5

Abstract

We have used several solid-state NMR techniques in conjunction with powder X-ray diffraction (XRD) and Raman spectroscopy to characterize the structure of the intermediate amorphous phases of AlPO 4-5 molecular sieve synthesis. The evolution of the gel phases as a function of crystallization time was followed by 31P and 27Al magic-angle spinning (MAS) NMR to obtain information on the local environments of Al and P atoms and by powder XRD to detect the long-range ordering of the gel samples. We have utilized 27Al/ 31P double-resonance techniques such as heteronuclear correlation spectroscopy (HETCOR) to select the 31P–O– 27Al bonding connectivities and transfer of populations by double-resonance (TRAPDOR) to obtain information regarding the degree of condensation for P sites in the amorphous phases. The 1H → 31P cross-polarization (CP) was used to identify the P sites with hydroxyl groups attached. Raman spectroscopy was also employed to follow the evaluation of the pore system. The 13C CP MAS spectra provide information regarding the chemical environment of template molecule in the gel. The work shows that a combination of the above-mentioned techniques can provide more detailed information on the structure of amorphous phases formed during hydrothermal synthesis.