F. Márquez

Denitrification of natural water on supported Pd/Cu catalysts

Abstract The influence of the support on the catalytic hydrogenation of nitrates in liquid phase was investigated. Pd/Cu supported on hydrotalcite and Pd/Cu supported on alumina catalysts were tested for this reaction and its activity and selectivity were compared. It has been observed a higher activity and a lower production of ammonium when the metals are supported on hydrotalcite than when they are supported on alumina. When rehydrated after calcination hydrotalcite recovers its layered structure. Nitrates can be located in the interlayer space diminishing the problems associated to mass transfer limitations and increasing the activity of the material. In addition, copper can be incorporated in the hydrotalcite structure by an isomorphical replacement of magnesium, obtaining thus a high dispersion of the copper centres, that is reflected in a higher activity if compared with copper impregnated samples. A XPS study was made in order to characterise the metals supported on the hydrotalcite.

On the researching of a new zeolite structure for the selective catalytic reduction of NO: The possibilities of Cu-exchanged IM5

A new zeolite (IM5) whose structure has not been resolved yet is tested for the selective catalytic reduction (SCR) of NO with C3H8 and characterized by in situ X-ray photoelectron spectroscopy. The catalytic behavior of copper exchanged IM5 zeolite is compared with that of copper exchanged ZSM5 zeolites. The influence of the partial pressure of oxygen, reaction temperature and exchange level of the metal in the catalyst is similar to that observed with copper exchanged ZSM5 zeolite, but Cu–IM5 is a more active and hydrothermically more stable catalyst than Cu–ZSM5.

Characterisation of the active copper species for the NOx removal on Cu/Mg/Al mixed oxides derived from hydrotalcites: an in situ XPS/XAES study

In situ X-ray photoelectron spectroscopy was used to characterise Cu/Mg/Al mixed oxides derived from hydrotalcites (catalyst used for the NOx removal reaction). The active sites are the copper centres: (i) Cu(0) for NO decomposition and (ii) Cu(0) and/or Cu(I) for NO reduction with a hydrocarbon. The ability of these materials to redisperse the copper active sites without destroying the structure of the material makes them different from other catalysts such as zeolites, and is essential for suitable catalytic behaviour at high temperatures.

Tuning the photocatalytic activity of titanium dioxide by encapsulation inside zeolites exemplified by the cases of thianthrene photooxygenation and horseradish peroxidase photodeactivation

A series of Y, Beta, mordenite and ZSM-5 zeolites containing different amounts of nanosized TiO2 clusters have been prepared by TiO2+ exchange followed by condensation. The presence of TiO2+ and its subsequent oligomerization can be followed in Raman spectroscopy by the appearance of the band at ca. 530 cm−1 and its replacement by others at 394, 460 and 637 nm. X-ray diffractograms of the solids show a considerable intensity decrease as the amount of TiO2 present increases. High-resolution transmission electron microscopy (HRTEM) shows that no isolated TiO2 particles are present in the case of zeolite Y, while the sample of mordenite at the highest Ti loading contains isolated TiO2 particles distinguishable by HRTEM. Diffuse reflectance UV-Vis spectroscopy indicates that the bandgap and the apparent extinction coefficient depend remarkably on the Ti content as well as on the zeolite crystal structure. Quantum chemical calculations at the semiempirical level also predict large variations in the HOMO–LUMO energies as a function of the number of Ti atoms. It has been found that the photoactivity of TiO2@Y and TiO2@mordenite is higher than that of commercial anatase for the photooxygenation of thianthrene to thianthrene oxide (λex>200 nm), but smaller for the hoseradish peroxidase photodeactivation in aqueous buffer (λex=350 nm). These variations in the photocatalytic activity of TiO2 illustrate the potential that inclusion of TiO2 nanoclusters within zeolites has to modulate its photoactivity.

‘Ship-in-a-Bottle’ Synthesis and Photochromism of Spiropyrans Encapsulated within Zeolite Y Supercages

Abstract The ship-in-a-bottle synthesis of three spiropyrans inside the NaY supercages was carried out by the condensation of 2-methylene-1,3,3-trimethylindoline with the appropriate substituted benzaldehyde. After the reaction, spiropyrans were detected in the supernatant and the zeolites became coloured. Combustion chemical and thermogravimetric analyses confirmed the presence of organic material within the solid. UV–Vis and Raman spectroscopies are compatible with the formation of the merocyanine form of the spiropyran photochromic system. Upon visible irradiation the solids bleach, and in some cases the coloration is regained upon standing in the dark for long periods. This abnormal photochromic behaviour is the reverse of that observed for the spiropyran/merocyanine system in ethanol and illustrates the possibility of zeolites as media to alter the molecular properties of incorporated guests.

EXFAS electron spectroscopy as a new tool of local characterisation of copper in Cu-Beta zeolite

Abstract EXFAS spectroscopy has been applied for the first time to the study of the local characterisation of reduced copper in zeolites. The oscillating features observed beyond the Cu M2,3VV Auger transition have been isolated and analysed following the standard EXAFS procedure.