Molecular Modeling, Multinuclear NMR, and Diffraction Studies in the Templated Synthesis and Characterization of the Aluminophosphate Molecular Sieve STA-2

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• 作者：Maria Castro ; Valerie R. Seymour ; Diego Carnevale ; John M. Griffin ; Sharon E. Ashbrook ; Paul A. Wright ; David C. Apperley ; Julia E. Parker ; Stephen P. Thompson ; Antoine Fecant ; Nicolas Bats
• 刊名：Journal of Physical Chemistry C
• 出版年：2010
• 出版时间：July 29, 2010
• 年：2010
• 卷：114
• 期：29
• 页码：12698-12710
• 全文大小：622K
• 年卷期：v.114,no.29(July 29, 2010)
• ISSN：1932-7455

文摘

Molecular modeling has been used to assist in the design of a new structure directing agent (SDA) for the synthesis of the AlPO₄ form of STA-2, bis-diazabicyclooctane-butane (BDAB). This is incorporated as a divalent cation within the large cages of STA-2, as determined via a combination of solid-state ¹³C and ¹⁵N MAS NMR, supported by ¹⁴N and ¹H-¹⁵N HMQC solution NMR and density functional calculations. As-prepared AlPO₄ STA-2 containing cationic SDA molecules achieves neutrality by the inclusion of hydroxide ions bridging between 5-fold coordinated framework Al atoms. Synchrotron X-ray powder diffraction data of the dehydrated as-prepared form indicates triclinic symmetry (Al₁₂P₁₂O₄₈(OH)₂·BDAB, P1, a = 12.3821(2) Å, b = 12.3795(2) Å, c = 12.3797(3) Å, α = 63.3585(8)°, β = 63.4830(7)°, γ = 63.4218(7)°) with the distortion from rhombohedral R symmetry resulting from the partial order of hydroxide ions in bridging Al−OH−Al sites within cancrinite cages. Upon calcination in oxygen, the organic SDA is removed, leaving AlPO₄ STA-2 with a pore volume of 0.22 cm³ g⁻¹ (R, Al₃₆P₃₆O₁₄₄, a = 12.9270(2) Å, c = 30.7976(4) Å). Dehydrated calcined AlPO₄ STA-2 has two crystallographically distinct P and Al sites: ³¹P MAS NMR resolves the two distinct P sites, and although ²⁷Al MAS NMR only partially resolves the two Al sites, they are separated by MQMAS. Furthermore, 2D ²⁷Al → ³¹P MQ-J-HETCOR correlation spectroscopy confirms that each framework Al is linked to the two different P sites via Al−O−P connections in a 3:1 ratio (and vice versa for P linked to different Al). The ²⁷Al and ³¹P resonances are assigned to the crystallographic Al and P sites by calculation of the NMR parameters using the CASTEP DFT program for an energy-minimized AlPO₄(SAT) framework.