Browsing by Author "Ribeiro, F. R."
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- An elegant way to increase acidity in SAPOs: use of methylamine as co-template during synthesisPublication . Fernandes, Auguste; Ribeiro, F. R.; Lourenço, J. P.; Gabelica, Z.SAPO-34 and SAPO-11 with an increased number of acid sites were synthesized by adding methylamine (MA) as co-template to tetraethylammonium hydroxide (TEAOH) or dipropylamine (DPA) respectively used as true templates.
- Characterization of stability and porosity of SAPO-40 using m-xylene as model reactionPublication . Lourenço, J. P.; Ribeiro, M. F.; Ribeiro, F. R.; Rocha, J.; Gabelica, Z.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.
- Generation of acid sites by incorporation of cobalt in the AFR structurePublication . Lourenço, J. P.; Ribeiro, M. F.; Ribeiro, F. R.; Rocha, J.; Gabelica, Z.; Onida, B.; Garrone, E.Pure CoAPO4-40 and CoAPSO-40 samples have been synthesized. The CoII <=> CoIII framework transformation, and hence the number of potential acid sites has been evaluated by spectroscopic techniques and using m-xylene isomerization as model reaction.
- Incorporation of cobalt in the AFR structure and characterization of the resulting acid sitesPublication . Lourenço, J. P.; Ribeiro, M. F.; Ribeiro, F. R.; Rocha, J.; Gabelica, Z.; Onida, B.; Garrone, E.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.
- Síntese e caracterização de silicoaluminofosfatos do tipo SAPO-40Publication . Lourenço, J. P.; Ribeiro, M. F.; Ribeiro, F. R.; Rocha, J.; Gabelica, Z.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.
- Solid-state NMR and powder XRD studies of the structure of SAPO-40 upon hydration-dehydration cyclesPublication . Lourenço, J. P.; Ribeiro, M. F.; Ribeiro, F. R.; Rocha, J.; Gabelica, Z.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.
- Study of catalytic properties of SAPO-40Publication . Lourenço, J. P.; Ribeiro, M. F.; Ribeiro, F. R.; Rocha, J.; Gabelica, Z.; Dumont, N.; Derouane, E. G.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.
- Synthesis and acidity characterization of CoAPO-37Publication . Costa, C. S.; Lourenço, J. P.; Henriques, C.; Antunes, A. P.; Ribeiro, F. R.; Ribeiro, M. F.; Gabelica, Z.A well-crystallized sample of CoAPO-37 was prepared. The incorporation of cobalt in the FAU structure framework was indirectly shown by FTIR spectroscopy, which shows peaks assigned to Bronstëd acid sites.
- Synthesis, characterization, and catalytic properties of AlPO4-40, CoAPO-40, and ZnAPO-40Publication . Lourenço, J. P.; Ribeiro, M. F.; Ribeiro, F. R.; Rocha, J.; Garrone, E.; Gabelica, Z.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.
- Thermal and hydrothermal stability of silicoaluminophosphate SAPO-40Publication . Lourenço, J. P.; Ribeiro, M. F.; Ribeiro, F. R.; Rocha, J.; Gabelica, Z.; Derouane, E. G.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.