Molecular modeling, multinuclear NMR, and diffraction studies in the templated synthesis and characterization of the aluminophosphate molecular sieve STA-2

Castro, Maria and Seymour, Valerie R. and Carnevale, Diego and Griffin, John M. and Ashbrook, Sharon E. and Wright, Paul A. and Apperley, David C. and Parker, Julia E. and Thompson, Stephen P. and Fecant, Antoine and Bats, Nicolas (2010) Molecular modeling, multinuclear NMR, and diffraction studies in the templated synthesis and characterization of the aluminophosphate molecular sieve STA-2. The Journal of Physical Chemistry C, 114 (29). pp. 12698-12710. ISSN 1932-7447

Abstract

Molecular modeling has been used to assist in the design of a new structure directing agent (SDA) for the synthesis of the AlPO(4) form of STA-2, bis-cliazabicyclooctane-butane (BDAB). This is incorporated as a divalent cation within the large cages of STA-2, as determined via a combination of solid-state (13)C and (15)N MAS NMR, supported by (14)N and (1)H-(15)N 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 (Al(12)P(12)O(48)(OH)(2)center dot BDAB, P1, a = 12.3821(2) angstrom, b = 12.3795(2) angstrom, c = 12.3797(3) angstrom, alpha = 63.3585(8)degrees, 63.4830(7)degrees, gamma = 63.4218(7)) with the distortion from rhombohedral R (3) over bar 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 AlPO(4) STA-2 with a pore volume of 0.22 cm(3) g(-1) (R (3) over bar, Al(36)P(36)O(144), a = 12.9270(2) angstrom, c = 30.7976(4) angstrom). Dehydrated calcined AlPO(4) STA-2 has two crystallographically distinct P and Al sites: (31)P MAS NMR resolves the two distinct P sites, and although 27AI MAS NMR only partially resolves the two Al sites, they are separated by MQMAS. Furthermore, 2D (27)Al -> (31)P MQ-J-HETCOR correlation spectroscopy confirms that each framework Al is linked to the two different P sites via AI-O-P connections in a 3:1 ratio (and vice versa for P linked to different Al). The (27)Al and (31)P 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 AlPO(4)(SAT) framework.