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

DOI: 10.1021/jp104120y DOI Help

Authors: Maria Castro (University of St Andrews) , Valerie Seymour (University of St Andrews) , Diego Carnevale (University of St Andrews) , John Griffin (University of St Andrews) , Sharon Ashbrook (University of St Andrews) , Paul Wright (University of St Andrews) , David Apperley (University of Durham) , Julia Parker (Diamond Light Source) , Stephen Thompson (Diamond Light Source) , Antoine Fecant (Institut Francais du Petrole-Lyon) , Nicolas Bats (Institut Francais du Petrole-Lyon)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of Physical Chemistry C , VOL 114 (29)

State: Published (Approved)
Published: July 2010

Abstract: 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.

Subject Areas: Chemistry, Physics

Instruments: I11-High Resolution Powder Diffraction

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