Cesare Oliva

Perovskite catalysts for the catalytic flameless combustion of methane: Preparation by flame-hydrolysis and characterisation by TPD–TPR-MS and EPR

Abstract A new method was employed for the preparation of a set of lanthanum cobaltites of general formula La1−xMxCoO3+δ with M=Ce, Eu and x=0, 0.05, 0.1, 0.2. All the samples thus prepared were nanostructured, thermally very stable and characterised by highly crystalline perovskite-like structure and high surface area. Their activity as catalysts for the catalytic flameless combustion (CFC) of methane was by ca. one order of magnitude higher than that of their analogues, prepared through the usual calcination-milling (CM) procedure. Adsorption of oxygen was accompanied by formation of paramagnetic species. Desorption of preadsorbed oxygen was dependent on the nature of the doping element and on the value of the stoichiometric coefficient x of their formula. A correlation between the temperature of the maximal rate of oxygen release and catalytic activity was found. The following scale of activity for the title reaction versus x values could be set up: 0.1Ce>0.05Ce>0>0.05Eu>0.1 Eu≅0.2Ce. The higher activity of Ce-doped catalysts as compared to those doped with Eu was found to be related to the strength of the bond between oxygen and Co ions.

Protective effect of the nitroxide tempol against the cardiotoxicity of adriamycin

Nitroxides are cell permeable, stable radicals that have been shown to exert antioxidant effects in several experimental models. In the present study, the ability of the piperidine nitroxide TEMPOL to prevent the acute cardiac toxicity of Adriamycin (ADR), which depends on oxygen-derived free radical generation, was assessed in isolated rat hearts. The results obtained show that TEMPOL (2.5 mM) significantly reduces the contractile impairment as well as the lipid peroxidation observed in rat heart preparations perfused with 100 micrograms/ml of ADR for 60 min. Both direct interaction with free radicals and decrease of Fe(II) availability (by stable oxidation and/or by chelation) seem to contribute to the cardioprotective effect to TEMPOL. HPLC and EPR studies of the subcellular distribution of TEMPOL indicate that substantial amounts of the nitroxide localize to the mitochondrial and microsomal fractions, in an ordered environment possibly corresponding to the interface between membrane and aqueous compartments.

Activity and deactivation of Fe-MFI catalysts for benzene hydroxylation to phenol by N2O

Abstract Isomorphously substituted Fe-MFI zeolite catalysts with various Si/Al and/or Si/Fe ratios were synthesized and characterized by many different techniques, such as ICP, XRD, SEM, TPR, microcalorimetry, FTIR, and EPR. Under standard reaction conditions the best catalyst gave 20% benzene conversion and over 90% selectivity to phenol. For Fe-ZSM5 catalysts, addition of steam to the feed improved catalyst activity, selectivity, and durability. Phenol formed onto Fe-based sites only. Active sites could very likely be composed of oxygen-bridged, extraframework binuclear Fe redox species, charge-compensating the framework Fe 3+ or Al 3+ ions. Surface acidity was not responsible for activity in the main reaction, but it was heavily involved in catalyst deactivation by coking. Catalyst deactivation derived mainly from the decomposition-condensation of phenol onto acid sites; the stronger the latter, the quicker was the coking rate.

Antiproliferative effect of the piperidine nitroxide TEMPOL on neoplastic and nonneoplastic mammalian cell lines.

The stable nitroxide 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPOL) is widely used as a probe in biophysical studies and as an antioxidant in several experimental models. The potential cytotoxic effects of TEMPOL were tested on a panel of human and rodent cell lines, and the nitroxide proved to be significantly more effective in inhibiting the growth of neoplastic than nonneoplastic cell lines after a 96-h exposure. More detailed studies on MCF-7/WT cells indicate that at least 24 h are necessary for TEMPOL to induce irreversible cell damage, which seems to be related to the reactivity of the nitroxyl group. This observation, together with the antagonistic effect of N-acetylcysteine, suggests an involvement of free radical-mediated processes. Cell cycle studies indicate a biphasic effect of TEMPOL, with a short-term accumulation of the cells in the G1 phase and a later increase in G2/M phase; the pattern of DNA fragmentation observed in TEMPOL-treated cells points to an apoptotic mode of cell death. In conclusion, our data suggest that, while the possible cytotoxic effects of TEMPOL should not be overlooked when using this compound as a biophysical probe or antioxidant, these same properties could be exploited as a novel approach to cancer chemotherapy, especially in tumor cells exhibiting unfavorable characteristics, such as a multidrug-resistant phenotype or loss of hormone receptors.

Characterisation of poly(ethylene terephthalate) and cotton fibres after cold SF6 plasma treatment

Poly(ethylene terephthalate) (PET) and cotton fibres, treated in an appositely set up RF SF6 plasma reactor under different operating conditions, were characterised by XPS, EPR, DSC, XRD, ATR analyses, water contact angle and water droplet roll-off angle measurements. The ageing of plasma-treated samples was also investigated under different post-treatment conditions. Plasma treatment led to efficient implantation of fluorine atoms on the surface of both polymers; this resulted in water repellence without altering the bulk properties of the polymers. The radical species formed in the plasma-activated polymer surface were involved in its fluorination and in the subsequent uptake of atmospheric oxygen. Surface reorganisation of polymer segments, tending to reduce the interfacial energy between the polymer and the phase in contact with it, induced the surface modifications observed under ageing and in samples plasma-treated several times. An increase in the depth of the fluorinated layer, leading to outstanding stable hydrorepellence, was achieved by repeated SF6 plasma treatments, followed by surface rearrangements favoured by swelling.

LaCeCo perovskites as catalysts for exhaust gas depollution

Abstract A series of La 1 − x Ce x CoO 3 + δ perovskite-type catalysts, with x ranging from 0 to 0.20, showed to be quite active for reduction of NO by CO (reaction 1) and for oxidation of CO by air oxygen (reaction 2) at temperatures ranging from 373 to 723 K. Analysis by X-ray diffraction, electron probe microanalysis, temperature-programmed desorption-temperature-programmed reaction and electron paramagnetic resonance, coupled with catalytic activity data, showed that the active sites on these catalysts are very likely localised onto Co ions, which coordinate O 2 − ions as intermediates for reaction 2, the latter taking place essentially through a suprafacial mechanism. For reaction 1, taking place through both a suprafacial and an intrafacial mechanism, the Co-based sites play also an additional role, favouring the electron transfer from site to site and so enhancing the transfer of oxygen species from surface to bulk and vice versa. Ce ions seem to act only as a stabiliser of O 2 − ions, helping in keeping them at the catalyst surface.

FT-IR and EPR spectroscopic analysis of La1−xCexCoO3 perovskite-like catalysts for NO reduction by CO

Abstract A FT-IR and EPR spectroscopic investigation has been carried out on a series of La 1− x Ce x CoO 3 ( x=0–0.15 ) perovskite-type catalysts, which are quite active for the reduction of NO by CO, and a mechanism has been proposed for this reaction. The first step involves the oxidation of CO by the catalyst, followed by the dissociative adsorption of NO onto the catalyst surface. Finally, adsorbed nitrogen (N ads ) yields N 2 O, N 2 and NCO ads along three parallel paths. Thus, oxygen exchange between NO and CO seems to occur indirectly and involves a surface oxygen vacancy. The catalytic activity is decreased by the substitution of Ce 4+ for La 3+ in the perovskite-type structure, which reduces the mobility of bulk oxygen. Activity is partially restored for x≥0.05 due to the presence of a segregated cerium oxide phase.

Electron paramagnetic resonance spectra of CeO2 catalyst for CO oxidation

The EPR spectra of freshly prepared CeO2 samples as well as of samples used as a catalyst in the oxidation of CO to CO2 are reported. Attribution of these patterns to oxygen species O2−, O2, O−, or to Ce3+ ions is discussed and dynamic phenomena involving these species are described. Bottlenecked systems between conduction electrons and Ce3+ ions are envoked to explain the observation of the Ce3+ EPR spectrum up to temperatures of about 370 K. Oxygen-deficient systems are obtained when the sample is used as a catalyst for CO oxidation in the presence of pyrex or quartz powder as a diluent, showing that the latter can play some role in stabilizing such species.

Charge ordering transition in GdBaCo2O5: Evidence of reentrant behavior

We present a detailed study on the charge ordering transition in a GdBaCo2O5.0 system by combining highresolution synchrotron powder/single-crystal diffraction with electron paramagnetic resonance experiments as a function of temperature. We found a second-order structural phase transition at T-CO=247 K (Pmmm to Pmma) associated with the onset of long-range charge ordering. At T-min approximate to 1.2T(CO), the electron paramagnetic resonance linewidth rapidly broadens, providing evidence of antiferromagnetic spin fluctuations. This likely indicates that, analogously to manganites, the long-range antiferromagnetic order in GdBaCo2O5.0 sets in at approximate to T-CO. Pair distribution function analysis of diffraction data revealed signatures of structural inhomogeneities at low temperature. By comparing the average and local bond valences, we found that above T-CO the local structure is consistent with a fully random occupation of Co2+ and Co3+ in a 1:1 ratio and with a complete charge ordering below T-CO. Below T approximate to 100 K the charge localization is partially melted at the local scale, suggesting a reentrant behavior of charge ordering. This result is supported by the weakening of superstructure reflections and the temperature evolution of electron paramagnetic resonance linewidth that is consistent with paramagnetic reentrant behavior reported in the GdBaCo2O5.5 parent compound.

Sorption-diffusion in molecular sieves: I. Evaluation of thermodynamic and kinetic parameters by the gas chromatographic pulse method

Abstract The gas chromatographic pulse method has been applied to the problem of the evaluation of thermodynamic and kinetic parameters relating to the sorption-diffusion of aromatic hydrocarbons in zeolites at relatively high temperature (613–713 K). Equations derived from the theory of moments and the procedure for collection of data and for their treatment have been adapted to the present case by proper adjustment and simplification, aiming at the separation of the effects of the various sorption-diffusion phenomena involved. The reliability of the parameters thereby evaluated, the probable errors involved and the limits and advantages of the method are discussed.