L. Marchese

On the hydrothermal stability of CuAPSO-34 microporous catalysts for N2O decomposition: a comparison with CuZSM-5

Abstract The hydrothermal stability of CuAPSO-34 microporous silicoaluminophosphates with chabasite structures has been investigated and compared to that of a copper-exchanged ZSM-5 zeolite by a combined XRD, FTIR, and catalytic study. CuAPSO-34 showed a higher hydrothermal structural stability (steaming 80xa0h at 600xa0°C), as found by XRD. Spectroscopic FTIR investigation of adsorbed CO revealed that upon this steaming procedure the concentration of monovalent copper ions in CuAPSO-34 was not significantly affected, whereas, even after a less severe steaming (60xa0h at 550xa0°C), these species dramatically decreased in CuZSM-5, and extraframework Al 3+ ions were simultaneously formed. Consequently, the high activity in N 2 O decomposition shown by fresh CuZSM-5 was essentially lost after steaming, while CuAPSO-34 exhibited a significantly milder deactivation.

Spectroscopic characterisation of microporous aluminophosphate materials with potential application in environmental catalysis

Abstract This review article deals with a spectroscopic characterisation, including FTIR, UV-Vis-NIR and NMR, of acid and redox microporous aluminophosphate catalysts with chabasite-related structure. These materials show high thermal and hydrothermal stability, and for this reason are attractive catalysts for environmental application. An extended investigation of acid SAPO-18 and SAPO-34, which are selective catalysts in methanol-to-olefins (MTO) and oxidative dehydrogenation (ODH) of light alkanes processes, will be presented. These catalysts can also be used as supports for the preparation of metal-containing molecular sieves for De-NOx reactions. Catalytic studies of NO oxidation to NO2 and N2O decomposition performed on cobalt- and copper-containing materials will be illustrated and correlated to spectroscopic results.

CuAPSO-34 Catalysts for N2O Decomposition in the Presence of H2O. A Study of Zeolitic Structure Stability in Comparison to Cu-SAPO-34 and Cu-ZSM-5

The structural stability at high temperatures of both Cu-exchanged SAPO-34 and CuAPSO-34 with isomorphously substituted copper ions has been investigated. SAPO-34 undergoes an extensive crystallinity loss upon copper ion exchange. The CuAPSO-34 framework showed good hydrothermal stability, as reflected in its surface area and X-ray diffraction pattern after ageing treatments. This catalyst exhibited good activity in N2O decomposition even when the reaction was run in the presence of H2O or after ageing treatment under H2O vapor at 600 °C for 80 h which, conversely, led to a drastic loss of activity of Cu-ZSM-5.

Evaluating the Catalytic Performances of SAPO-34 Catalysts for the Oxidative Dehydrogenation of Ethane

Acid silicoaluminophosphate SAPO-34 catalysts with a chabasite-related (CHA) structure were tested for the oxidative dehydrogenation of ethane in the temperature range 550-700 °C achieving very interesting catalytic performances (about 70% C2H4 selectivity at 45% ethane conversion) which were related to both Lewis and Brønsted acid sites, as found by a NH3-TPD study.

V-MCM-22: Synthesis and characterization of a novel molecular sieve

Abstract This work presents the synthesis and spectroscopic characterization of V-MCM-22, a novel molecular sieve. The synthesis was performed under static hydrothermal crystallization, using VOSO 4 as source of vanadium at SiO 2 /V 2 O 3 = 66 and hexamethyleneimine as structure-directing agent. Aluminum was also incorporated in the structure at SiO 2 /Al 2 O 3 ratios (SAR) of 50 and 80, named V-MCM-22 (50) and V-MCM-22 (80) respectively. Only V-MCM-22 (50) showed higher crystallinity than the parent MCM-22. The insertion of vanadium ions in the framework sites was confirmed by diffuse reflectance (DR) UV-Vis and FTIR spectroscopy, the latter using CO adsorption at 100K. The V-MCM-22 (50) sample presented V in the 5+ state after calcination of the template; two families of vanadium sites were found: a family of distorted tetrahedral oxovanadium (SiO) 3 V=O species absorbing at 290, 250 and 330 nm which underwent a reduction to V IV (d-d transition at 550 nm) after treatment in H 2 at 500°C, and a family of tetrahedral oxovanadium with a lower distortion degree, which showed bands at 225, 245 and 265 nm. The latter species were stable after reduction. Hydroxyls bound either to the Lewis vanadium centers or to partially extra-framework Al ions were detected by FTIR and their acidity monitored by CO adsorption. The stretching frequency of these hydroxyls showed a red-shift of ca. 200 cm 1 by CO adsorption which suggests an acidity intermediate between silanols (90 cm 1 ) and bridged SiO(H)Al groups (320 cm 1 ). This material is a good candidate for selective oxidation reactions of organic molecules.

Vanadium-modified MCM-22 zeolite

The synthesis and the characterization of a novel vanadoaluminosilicate V-MCM-22, with MWW structure, and of vanadyl-exchanged MCM-22 zeolite, [VO]-MCM-22, have been performed. V-MCM-22 was prepared using VOSO 4 in the synthesis gel (H + or Na + -exchanged samples were also prepared), while [VO]-MCM-22 was prepared by ion-exchange of MCM-22 with VO 2+ ions. The materials were characterized by X-ray diffraction (XRD) and thermogravimetry (TGA). The presence of redox sites (V 4+ /V 5+ couples) was monitored by diffuse reflectance (DR) UV-Vis spectroscopy of oxidized (in O 2 at 580°C) and reduced (in H 2 at 500°C) samples.

Spectroscopic and catalytic studies on Cu-MCM-22: Effect of copper loading

Copper exchanged MCM-22 zeolites with varying copper contents were prepared, characterized and tested in the nitrous oxide decomposition. Over-exchanged samples showed high activity, comparable to very active Cu-ZSM-5 catalysts. The nature of the copper species was investigated by TPR-H 2 , FTIR-CO and FTIR-NO, evidencing at least three different species: exchanged Cu 2+ ions, cationic oligomeric species and oxidic phases. Upon NO adsorption, mononitrosilic complexes Cu I -(NO) were formed, and completely oxidized to Cu II -(NO) with increasing NO pressure. Nitrate complexes were extensively formed by reaction with the oxidic phases in the sample with 183% cation exchange level.

SYNTHESIS, MORPHOLOGY AND STRUCTURAL PROPERTIES OF (GD,ND)SR2RUCU2O8 SAMPLES

NdSr2RuCu2Ox material has been prepared as polycrystalline powder by solid state reaction. The compound has been investigated by synchrotron x-ray powder diffraction and scanning electron microscopy. The experimental results show that the average crystal structure is a disordered cubic perovskite with Nd and Sr cations occupying the same site and the same substitution is found for Cu and Ru atoms. A comparison between the crystal structure and morphology of this compound and the superconducting tetragonal GdSr2RuCu2O8 is also discussed.

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.