João P. Lourenço

Structure analysis of the novel microporous aluminophosphate IST-1 using synchrotron powder diffraction data and HETCOR MAS NMR

Abstract A combination of advanced powder diffraction and NMR techniques have allowed the structure of the novel microporous aluminophosphate IST-1 ( | (CH3NH2)4(CH3NH3+)4(OH−)4 | [ Al12P12O48 ] ) to be elucidated. The framework structure was determined in the non-centrosymmetric space group Pca21 (a=9.61523(1) A, b=8.67024(1) A, c=16.21957(2) A) from high-resolution synchrotron powder diffraction data using the program FOCUS. Extra framework species were then located on difference electron density maps. A hydroxyl group was found to bridge between two of the framework Al atoms, and one methylamine species, presumably protonated, could be located in the channels where it H-bonds to three framework oxygens. The most unusual feature of the structure is the second methylamine molecule, which bonds directly to a framework Al atom. The structure is entirely consistent with 31P and 27Al MAS NMR studies, which showed there to be three P (all 4-coordinate) and three Al (one 4-, one 5- and one 6-coordinate) sites, and with 13C MAS NMR, which showed there to be two different types of methylamine species in equal amounts. Assignment of the 31P, 27Al and 13C MAS NMR signals could be deduced from the crystallographic data,31P-27Al HETCOR spectra and ab initio calculations.

Synthesis and characterization of new CoAPSO-40 and ZnAPSO-40 molecular sieves. Influence of the composition on the thermal and hydrothermal stability of AlPO4-40-based materials

Abstract Highly crystalline CoAPSO-40 and ZnAPSO-40 have been synthesized and characterized by powder XRD, TG/DSC, SEM, EDX, 27Al, 31P and 29Si solid-state NMR, diffuse reflectance UV–VIS spectroscopy, FT IR and catalytic tests using the m-xylene isomerization and n-heptane cracking as model reactions. The simultaneous incorporation of silicon and a divalent metal in the framework of the AFR structure results in the generation of Bronsted acid sites similar to those found in SAPO-40 and MeAPO-40. The catalytic activity of the samples for acid catalyzed reactions is higher than that of SAPO-40 with a homogeneous framework silicon distribution. The framework incorporation of cobalt or zinc results in a decrease of the thermal and hydrothermal stability of the metal bearing AFR framework, when compared with AlPO4-40 and SAPO-40.

Study of catalytic properties of SAPO-40

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.

Thermal and hydrothermal stability of the silicoaluminophosphate SAPO-40

Abstract 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.

Synthesis, characterization, and catalytic properties of AlPO4.40, CoAPO-40, and ZnAPO-40

The experimental conditions leading to the synthesis of pure and highly crystalline AlPO 4 -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, 13 C, 27 AI, and 31 P solid-state n.m.r., diffuse reflectance u.v.-vis spectroscopy, FT i.r., and catalytic tests using the m -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.

Multiple-quantum 27Al MAS n.m.r. spectroscopy of microporous AlPO-40 and SAPO-40

Two-dimensional triple and quintuple-quantum 27 Al magic-angle spinning (MQ MAS ) n.m.r. spectra of microporous AIPO-40 and SAPO-40 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 3Q 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 MQ 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 27 Al MAS n.m.r. together with 31 P MAS n.m.r. evidence discard an orthorhombic, Pccn , and monoclinic, P112/n , structure for as-prepared or calcined dehydrated AlPO-40, suggesting a space group with even lower symmetry that proposed to date.

Gas-phase dehydration of glycerol over thermally-stable SAPO-40 catalyst

SAPO-40 was used as a catalyst for the gas-phase dehydration of glycerol towards acrolein. At 350 °C the catalyst attained full conversion of glycerol with a negligible deactivation in the first 48 h, a glycerol conversion above 50% after 120 h on stream and a nearly constant selectivity to acrolein above 70%. This catalyst proved to be highly resistant under the experimental conditions used and can be regenerated without loss of activity or significant structural damage. The comparison of SAPO-40 with SAPO-34 and SAPO-11 illustrates the importance of the porous structure and emphasizes the good catalytic performance of this material.

Characterization of stability and porosity of SAPO-40 using m-xylene as model reaction

Abstract 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.

An elegant way to increase acidity in SAPOs: use of methylamine as co-template during synthesis

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 currently used as true templates. Along with minor changes of the final chemical and morphological properties of the as-synthesized materials, the major role of methylamine was shown to prevent a rapid silica polymerization (or to slow down its depolymerization) in the early synthesis steps, thereby favoring the progressive framework insertion of small Si oligomers that further generate an increased number of SAPO domains, with respect to Si islands.

Charged pullulan derivatives for the development of nanocarriers by polyelectrolyte complexation

Pullulan, a neutral polysaccharide, was chemically modified in order to obtain two charged derivatives: reaction with SO3(.)DMF complex afforded a sulfate derivative (SP), while reaction with glycidyltrimethylammonium chloride gave a quaternary ammonium salt (AP). The presence of the charged groups was confirmed by FTIR. Assessment of the positions where the reaction took place was based on (1)H- and (13)C NMR (COSY, HSQC-TOCSY, HSQC-DEPT, and HMBC) experiments. Estimation of the degree of substitution (DS) was made from elemental analysis data, and further confirmed by NMR peak areas in the case of AP. These new derivatives showed the capability to condense with each other, forming nanoparticles with the ability to associate a model protein (BSA) and displaying adequate size for drug delivery applications, therefore making them good candidates for the production of pullulan-based nanocarriers by polyelectrolyte complexation.