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Two-dimensional triple- and quintuple-quantum 27AI magic-angle spinning (MO MAS) n.m.r. spectra of microporous AIPO-40 and SAPOBO have been recorded at 9.4 and 14.1 T. The resolution of the 5Q spectra of AIPO-40 is amazing, at least 11 resonances being resolved. The 3lQ spectra further reveal the presence of 2 other much fainter peaks. Because the AIPO-40 aluminium sites have different quadrupole coupling constants the 9.4 T spectra are slightly better resolved than the 14.1 T spectra, suggesting that in MO n.m.r. it may sometimes be advantageous to work at lower magnetic fields. The 3Q spectra of SAPO-40 are poorly resolved displaying a main broad peak and two faint resonances. This is because the introduction of even a small amount of Si into the framework of AIPO-40 generates a distribution of Al sites and a dispersion of chemical shifts. MQ 27AI MAS n.m.r. together with 31P MAS n.m.r. evidence discard an orthorhombic, Pccn, and monoclinic, P172/n, structure for as-prepared or calcined dehydrated AIPO-40, suggesting a space group with even lower symmetry that proposed to date.

The experimental conditions leading to the synthesis of pure and highly crystalline AlPO,-40, CoAPO-40, and ZnAPO-40 have been optimized. Although the preparation of these phases is favored by the presence of TMA+ in the synthesis gel, these ions have not been found incorporated in the final AFR structures. All materials have been characterized by powder XRD, t.g./d.s.c., SEM, EDX, 13C, 27AI, and 3’P solid-state n.m.r., diffuse reflectance u.v.-vis spectroscopy, FTi.r., and catalytic tests using the n-t-xylene isomerization as a model reaction. This multitechnique approach provides strong evidence for the framework incorporation of cobalt and zinc. The acid sites generated by the framework insertion of cobalt and zinc are stronger than those generated by the incorporation of silicon.

The AFR structure with the silicoaluminophosphate composition (SAPO-40) was known since 1984. However the synthesis of AIPO4-40 and MeAPO4-40 (Me:Co, Zn) was only reported in 1994, hence offering new potential applications of this structure.

Estudo sobre a participacao do fotoperiodo nas variacoes sazonais de ingestao de alimentos, ganho de peso, crescimento especifico e absorcao de proteina no intestino da tilapia do Nilo. Durante 30 dias, foram utilizados 64 peixes, divididos em dois grupos, mantidos em aquarios de vidro (4 peixes por aquario, agua em 25oC), sem comunicacao quimica ou visual, submetidos a dois regimes de luminosidade (14L:10E, regime de 14h/luz e 10h de escuro, e 10L:14E, regime de 10h/luz e 14h de escuro). A ingestao de alimentos foi determinada a cada dez dias e ao final do periodo. A absorcao, avaliada a cada dez dias e todas as outras variaveis determinadas ao final do periodo experimental. Foi observado que, durante o periodo experimental de verao, houve aumento de ingestao de alimentos em ambos fotoperiodos (p>0,05). No inverno, a diferenca entre os fotoperiodos nao foi significante. As medias de 30 dias de ingestao e de ganho de peso diminuiram no inverno, porem, com diferenca significante nos animais submetidos ao fotoperiodo 10L:14E. Houve diferenca estatisticamente significante entre as estacoes na taxa de crescimento especifico dos peixes e, ainda, entre os fotoperiodos no inverno. Os resultados sugerem que existe alteracao sazonal da ingestao, ganho de peso e na taxa de crescimento especifico em tilapia e que o fotoperiodo esta fortemente envolvido nessa resposta. Made available in DSpace on 2019-04-16T00:38:09Z (GMT). No. of bitstreams: 1 VARIACOESSAZONAIS.pdf: 21442839 bytes, checksum: 33ecc0c593f87ca5f823d2b6483d35bf (MD5) Previous issue date: 1996 Dissertação (Mestrado em Ciências Biológicas) - Universidade Estadual Paulista, Botucatu.

FTIR, MAS 1H-NMR, and molecular graphics data are reported concerning the hydroxyl species in a series of SAPO-40 samples with variable Si contents, as well as FTIR data concerning the interaction of ammonia with the different acid sites. Up to seven types of Si(OH)Al Brønsted sites are present, mainly differing by the O-H stretching frequency. Three high-frequency bands (3637-3624 cm-1) correspond to hydroxyls located in the 12-member channels and two low-frequency bands (3559 and 3528 cm-1) to OH species in eight-member rings and side pockets of the AFR structure. Two bands at exceptionally low frequency (3485 and 3445 cm-1 ) are due to OH species interacting with silica islands. All low-frequency bands behave with temperature as H-bonded species. All types of hydroxyls form ammonium ions, the thermal decomposition of which shows some difference in acidity among the OH species. IR evidence indicates that NH4 + species interact strongly with the basic oxygen atoms of the lattice. No Lewis sites were evidenced by ammonia adsorption.

The thermal and hydrothermal stability of SAPO-40 has been evaluated using the isomerization of m-xylene as model reaction. The characterization of the porosity was also studied and compared to other well known structures, namely Y zeolite, mordenite and ZSM-5. The structural changes that occur under thermal treatments influence the activity and selectivity of SAPO-40, while hydrothermal treatments do not significantly change those properties. The results confirm the high stability of SAPO-40 under thermal and hydrothermal treatments. Catalytic tests and adsorption of cyclohexane indicate that regular large side pockets or lobes exist along the main channels of SAPO-40, which create a large void volume responsible for the high rate of adsorption, high amount of adsorbed cyclohexane and the low shape selectivity in m-xylene isomerization.

It is well known that after the removal of the template many porous aluminophosphates and related materials are very sensitive to water.' Depending on the type of structure, reversible or irreversible phase transitions, loss of crystallinity and changes in the coordination of some framework A1 upon rehydration are observed. For example, solid-state NMR shows that the rehydration of SAPO-5 leads to the formation of octahedral Al. Subsequent dehydration restores the initial tetrahedral coordination of Al. Template-free SAPO-37 becomes totally amorphous to X-rays after exposure to water and stays so after subsequent thermal treatment^.,,^ In contrast, Barthomeuf and co-workers have shown recently, that, on hydration, template-free SAPO-34, an analogue of chabasite, shows the opening of some Si-0-A1 bonds, the effect being reversible upon dehydrati~n.T~h e hydrated distorted structure was found to be stable for months with no further modifications and the ordered material could be regenerated by removal of water. Here we wish to report that the structure of template-free SAPO-40 undergoes a similar reversible modification.

Thermal and hydrothermal stability of SAPO-40 were studied by X-ray powder diffraction (XRD) and magic-angle spinning nuclear magnetic resonance (MAS-NMR). For the X-ray study, the hydrothermal treatments were carried out, in situ, in a high-temperature chamber. The SAPO-40 structure shows a remarkable stability to high temperatures under both dry and humid air. At high temperatures a reorganisation of silicon occurs, but the long-range order is only lost above ca. 1000°C. Changes in the XRD pattern induced by water at room temperature are completely reversible upon re-heating at 200°C, as well as the changes in the coordination and local environments of aluminium and phosphorus observed by NMR. For silicon however, some changes, that are observed upon hydration, remain after dehydration.

Os aluminofosfatos e silicoaluminofosfatos constituem duas das novas famílias de sólidos microporosos com estrutura tipo zeolítico. Estes materiais que apresentam elevada estabilidade térmica e hidrotérmica,podem possuir propriedades ácidas importantes, que associadas à sua estrutura de poros, lhes conferem novas e interessantes potencialidades de utilização no domínio da catálise, adsorção e permuta iónica.

A series of SAPO-40 samples with Si atomic fraction from 0.06 to 0.12 has been synthesised. The study of their catalytic properties has been evaluated by comparison with SAPO-37, USHY and mordenite, using as model reaction the cracking of n-heptane. The catalytic activity of SAPO-40 samples depends on the Si content, and is probably associated with the non-uniform distribution of silicon. SAPO-40 showed a stronger acidity than SAPO-37 with a similar Si content. SAPO-40 is more resistant to deactivation by coke than the studied mordenite sample. Its selectivity for cracking products is comparable to USHY, but hydrogen transfer is lower for SAPO-40 than for USHY and mordenite.

Submitted by Duarte Meireles (duarte@iseg.ulisboa.pt) on 2015-10-20T12:27:38Z No. of bitstreams: 1 ee-jsl-1984.pdf: 415056 bytes, checksum: 82b0fc3d81897012b7e7cb4fdcb8bad2 (MD5) Made available in DSpace on 2015-10-20T12:27:38Z (GMT). No. of bitstreams: 1 ee-jsl-1984.pdf: 415056 bytes, checksum: 82b0fc3d81897012b7e7cb4fdcb8bad2 (MD5) Previous issue date: 1984