Crystallization of magnesium substituted aluminophosphate of type-36 as studied by solid-state NMR spectroscopy

✍ Scribed by Jun Xu; Dan Zhou; Xiaowei Song; Lei Chen; Jihong Yu; Chaohui Ye; Feng Deng

• Book ID: 104055702
• Publisher: Elsevier Science
• Year: 2008
• Tongue: English
• Weight: 738 KB
• Volume: 115
• Category: Article
• ISSN: 1387-1811
• DOI: 10.1016/j.micromeso.2008.02.037

✦ Synopsis

The crystallization process of aluminophosphate molecular sieve MgAPO-36 is characterized by the evolution of intermediate gels. Multinuclear solid-state NMR techniques in combination with powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM) reveal in detail the nature of the intermediate gels and their evolution into crystalline structure. The long-range ordering of the aged as well as heated intermediate gels are probed by PXRD, showing that the crystallization of the framework begins after heating the gels at 423 K for 1.5 h. 31 P NMR indicated that the structural Al-O-P and Mg-O-P units from the ATS framework are formed at the same time. More information about the local ordering of the gels is obtained from two-dimensional 27 Al ? 31 P HETCOR and 1 H ? 31 P CP/MAS experiments. Two types of microstructure regions could be differentiated by partially and fully condensed P species, in which five types of P(nAl) (n = 2-4) units are identified by 31 P/ 27 Al double-resonance experiments. A possible evolution mechanism consisting of three stages is proposed for the crystallization process.