Erica C. Oliveira

Synthesis and surface properties of Ti-containing mesoporous aluminophosphates. A comparison with Ti-grafted mesoporous silica Ti-MCM-41

Abstract Mesoporous aluminophosphates (ALPO) was synthesised using cetyltrimethylammonium bromide (CTMABr) as a structure-directing agent, phosphoric acid and aluminum sulfate as sources of structure elements. Ti(IV) ions were introduced into mesoporous ALPO by grafting titanocene dichloride, [Cp 2 TiCl 2 ], onto the POH and AlOH groups exposed in the channels. FTIR spectroscopy was used to study surface hydroxyls, and by the use of NH 3 as molecular probe, to assess the surface acidity of both meso -ALPO and meso -Ti-ALPO materials. The coordination of Ti(IV) centres in Ti-ALPO material was studied using DR UV–Vis spectroscopy.

Acidity of mesoporous aluminophosphates and silicas MCM-41. A combined FTIR and UV-Vis-NIR study

The surface acidity of new mesoporous aluminophosphates, silicoaluminophosphates and [Si]-MCM-41 was studied by means of FTIR and DR UV-Vis-NR spectroscopies using ammonia as probe molecule. Moreover, a novel Ti-grafted mesoporous ALPO was synthesised and studied by the use of DR-UV-Vis spectroscopy.

The surface acidity of mesoporous silicoaluminophosphates: A FTIR study

Abstract Thermally stable mesoporous ALPO and SAPO (Si/Al=0.6) were synthesised using aluminum sulphate as aluminum source and without the need of HF as mineralizing agent. The mesophases prepared by this procedure were stable to calcination at 773K and presented a structure of non-parallel mesopores in the calcined form. FT-IR spectroscopy supplemented by the use of CO and NH 3 as probe molecules was used to monitor the surface acidity of these new mesoporous materials and indicated that Al-OH, P-OH groups for meso-ALPO and additionally SiOH groups for meso-SAPO are found on the surface of these molecular sieves. The acidities of P-OH and Al-OH are stronger than SiOH in mesoporous silicas but still weaker than the zeolitic Bronsted acid sites.

Cu-MCM-22 zeolite: A combined X-ray powder diffraction and computational study of the local structure of extra-framework copper ions

Abstract Local structure and site distribution of extra-framework copper ions in Cu-exchanged MCM-22 zeolite have been determined by synchrotron radiation X-ray powder diffraction analysis combined with ab-initio molecular orbital (DFT) calculations. Three Cu sites (S I , S II and S III ) in 6-membered rings and one site (Svi) in a 5-membered ring close to the interlamellar region, were located inside the MCM-22 supercage, whereas no Cu ions were found within the sinusoidal channels. The existence of two families of Cu sites (in 5- and 6-membered rings respectively) with different steric hindrance and adsorptive capacity, as indicated by previous FTIR study of adsorbed NO [A. Frache, et al., Langmuir, 18 (2002) 6875], was fully confirmed in this study.

The transformation of lamellar AlPO-kanemite into chabazite-type CAL-1 3D molecular sieve: a structural study

The preparation of a new molecular sieve, CAL-1, was recently reported. It presented a chabazite-type structure and was prepared starting from a lamellar aluminophosphate (ALPO-ntu), analogous to silica kanemite, and hexamethyleneimine as structure directing agent. Calcination of CAL-1 causes the transformation to H-SAPO-34, a molecular sieve for acid-catalyzed methanol-to-olefins reactions. An ex-situ high-resolution synchrotron radiation X-ray powder diffraction experiment allowed to monitor the relevant steps of the ALPO-ntu to CAL-1 transformation and its subsequent calcination to H-SAPO-34.

The stability of H-MCM-22 under severe thermal conditions

Abstract This study shows that the MWW structure is more stable than previously known zeolites. Structural, thermal and spectroscopic analyses have shown that acid MCM-22 zeolite is stable up to 1373K under vacuum and to 1473K in air. The Bronsted hydroxyl groups withstand temperatures up to 1173K. At 1473K there is a phase transition from the MWW structure into α-cristobalite when the sample is under vacuum while for the sample treated in air only a small fraction of the total is transformed to α-cristobalite at 1473K.

Replication by molecular sieves: controlling the properties of porous carbon by the use of porous oxides

Abstract Carbon materials with controlled porosity can be prepared by the use of inorganic templates, such as molecular sieves or zeolites, to direct their syntheses and structures. These materials are interesting due to their magnetic and physical electronic properties as well as the numerous possibilities in the catalysis field. To master the properties of the nanostructured carbon materials it is paramount to learn to control the area and porosity of these solids. This knowledge will allow qualitative growth in the application of these exceptional solids in heterogeneous catalysis and the construction of devices, sensors and biosensors.

Is water really deleterious for organometallics anchoring into zeolites

Anchoring of [(η5-C5H5)Rh(η4-C8H12)] into cavities of Na56Y and H56Y zeolites was studied. In contrast to expectation, the zeolite degree of hydration is not a key factor in the organometallic structural integrity. The thermal behavior of the occlusion reaction is the same when the zeolites are completely or partially dehydrated, showing that total absence of water is not a necessary condition to prepare an organometallic/zeolite system. For the zeolite Na56Y the product is the organometallic fragment [(η5-C5H5)Rh] which anchors to the oxygen atoms of the framework, while for the H56Y zeolite the product is a cationic organometallic species.