Ž . Solid State Nuclear Magnetic Resonance 8 1997 185–194 A solid-state NMR study of the molecular sieve VPI–5 synthesized in the presence of a CTABr surfactant Teresa Blasco a, ) , Joaquın Perez-Pariente b , Waclaw Kolodziejski c ´ ´ a ( ) Instituto de Tecnologıa Quımica UPV–CSIC , UniÕersidad Politecnica de Valencia, AÕda. de los Naranjos, s r n 46022-Valencia, Spain ´ ´ ´ b ( ) Instituto de Catalisis y Petroleoquımica CSIC , Campus UniÕersitario de Cantoblanco, 28049-Madrid, Spain ´ ´ c Department of Inorganic and Analytical Chemistry, Faculty of Pharmacy, Warsaw Medical Academy, Banacha 1, 02-097 Warszawa, Poland Received 3 December 1996; accepted 28 January 1997 Abstract Silicon-free and silicon-rich large-pore aluminophospate VPI–5, synthesized with various contents of AlPO–H3 Ž . Ž . Ž . impurity, was studied by Bloch decay BD and cross polarization CP NMR under magic angle spinning MAS . The 1 H ™ 31 P CP peaks were considerably stronger from AlPO–H3 than from VPI–5. A detailed examination of the CP kinetics and a careful comparison of the CP and BD spectra are prerequisites for the unequivocal interpretation of 1 H ™ 31 P CP in porous aluminophosphates. q 1997 Elsevier Science B.V. 1. Introduction The large-pore molecular sieve VPI–5, discov- w x ered by Davis et al. in 1988 1,2 , is a member of the AlPO family. The electrically neutral framework of 4 this interesting aluminophosphate contains parallel channels, 1.2 nm in diameter, circumscribed by 18- Ž . member rings of alternating Al and P atoms Fig. 1 . As-synthesised VPI–5 is normally free of organic material, although a template is present in a synthesis gel. Instead, the voids are filled up to 25 wt% with water and this has a unique three-dimensional struc- ture composed of hydrogen-bonded molecules form- w x ing triple helices, which run along the channels 3,4 . ) Corresponding author. Instituto de Tecnologıa Quımica ´ ´ UPV–CSIC, Avda. de los Naranjos, srn-46022 Valencia, Spain. Tel.: 34-6-387 78 12. Fax: 34-6-387 78 09. Because of the large size of the pores, VPI–5 has a potential capability of processing bulk organic molecules, which is of great interest from the cat- alytic point of view. Thus there have been several attempts to substitute Si for P in AlPO materials 4 w x 5–11 in order to create negative charges in the framework, which could be protonated to form acid sites active in catalysis. On the other hand, negative charges can also be neutralized by protonated or- ganic molecules occluded in Si-containing VPI–5 Ž . w x Si-VPI–5 8–11 . However, Si-VPI–5 with a rela- tively high Si content usually has large silica do- mains originating from the preferential substitution of neighbouring Al and P atoms by two Si atoms Ž substitution mechanism SM3 as proposed by Flani- w x. w x gen et al. 12 5–7 . It would be preferable to substitute a single Si atom for a single P atom Ž . substitution mechanism SM2 , but such substitution is normally possible only for a very low Si content wx 8. 0926-2040r97r$17.00 q 1997 Elsevier Science B.V. All rights reserved. Ž . PII S0926-2040 97 00004-0