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Abstract  

Several powder samples of TiO2 are pretreated thermally at 300, 480 and 540°C, subjected to -irradiation and after irradiation added in one of the compartment of the concentration cell made up of Ag/Ag+. The adsorbed oxygen species O 2ad , HO 2ad and O ad on TiO2 provide negatively charged sites and develop EMF in the cell. The radiation damage, measured in terms of equilibrium EMF, received at lower doses is partially recovered at higher doses. It is proposed that in heating at 480°C, ad species react with Ti3+ ions in the surface and produce –O–O– peroxy linkages and block the negatively charged sites while in heating at 540°C Ti4O7 phase is produced on the surface which adsorbs O2 and provide large number of negatively charged sites. During -irradiation peroxy linkages are broken and the Ti4O7 phase is destroyed. Observed oscillatory variation in equilibrium EMF is explained on the basis of several reactions mentioned above proceeding at different rates during radiolysis.

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Abstract  

TG, FTIR-(CO absorption), and catalytic activity in the NO reduction by CO were used to characterize Cu/Al2O3-TiO2 catalysts prepared by co-gelling aluminum tri-sec-butoxide and titanium iso-propoxide at pH 9 and at pH 3 gelling conditions. Under nitrogen flow, copper oxide decomposition, oxygen storage capacity (OSC) and sample dehydroxylation (total mass loss) was followed by TG. The CuO decomposition forming Cu0, Cu+1 was observed by means of FTIR (CO absorption) spectra. In pH 9 sample the large amount of Cu0 was observed. At low total mass loss and high Cu0/Cu+1+Cu+2 ratio (pH 9 sample) a lowest light-off in the NO reduction by CO was observed.

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Abstract  

The performances of selective catalytic reduction (SCR) by CO/H2 over two Pd/TiO2/Al2O3 catalysts prepared from PdCl2 and Pd(NO3)2 precursors were compared. The catalytic activities (NOx conversion and N2 yield) were measured on these two catalysts. The catalytic properties of the prepared catalysts were studied by various characterization techniques such as BET, CO-chemisorption, TEM, XPS, and TPD. The Pd precursors influenced the Pd particle distribution, resulting in different catalytic activities.

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The processes of crystallization of fibres (diameter 10–15μm) and coarse powders (grain size 500–1000μm) with four compositions in the system SiO2-Li2O-TiO2-Al2O3 were studied by conventional and in situ high-temperature XRD, DTA, SEM and optical microscopy. Activation energies of crystallization and morphological indices were deduced from the kinetic curves obtained by recording the high-temperature XRD peak intensity as a function of time. The glass-ceramic fibres drawn from compositions which exhibit glass-inglass phase separation show prevailing not-oriented bulk crystallization, whereas prevailing surface crystallization was found for single-phase glass fibres. Homogeneously-dispersed crystallization was obtained on heating fibres of these compositions. The partially cocrystallized glass fibres of eutectic composition between Li-metasilicate andβ-spodumene gave rise to a very fine and homogeneously-dispersed sub-microstructure.

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Journal of Thermal Analysis and Calorimetry
Authors:
F. Vieira
,
Soraia Souza
,
A. Oliveira
,
S. Lima
,
E. Longo
,
C. Paskocimas
,
L. Soledade
,
A. Souza
, and
Iêda Santos

Abstract  

In this study undoped and Cr, Sb or Mo doped TiO2 were synthesized by polymeric precursor method and characterized by X-ray diffraction, UV–VIS spectroscopy, infrared spectroscopy and thermogravimetry (TG). The TG curves showed a continuous mass loss assigned to the hydroxyl elimination and Cr6+ reduction. Doped TiO2 samples showed a higher mass loss assigned to water and gas elimination at lower temperatures. In these doped materials a decrease in the anatase–rutile phase transition temperature was observed. After calcination at 1,000 °C, rutile was obtained as a single phase material without the presence of Cr6+.

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Abstract  

Thermal analysis has been used to evaluate the stability, glass transition, and water retention of Nafion based polymer–ceramic electrolytes. These electrolytes are envisioned as promising replacement of Nafion in fuel cells operating above 100 °C. The polymeric matrix prepared by casting exhibits lower crystallinity than the extruded Nafion, a feature that affects the water absorption properties. The addition of titania-based nanotubes and nanoparticles to the polymer has enhanced the water retention at high temperatures (~130 °C) and the glass transition temperature, respectively. Such results are important for the design of composite electrolytes for the operation of fuel cells at high temperatures.

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Abstract  

The objective of this study is to evaluate the use of titanium dioxide nanoparticles which were prepared by novel sonochemical method as an ion exchange material for the removal of Sr from aqueous solution. The pH effect on the Sr2+ sorption was investigated. The data obtained have been correlated with Freundlich, Temkin and Dubinin–Radushkevich (D–R) isotherm models. Thermodynamic parameters fort he sorption system have been determined at four temperatures. Simple kinetic models have been applied to the rate and isotherm sorption data and the relevant kinetic parameters were determined from the graphical presentation of these models at 298°K. Results explained that the pseudo second-order sorption mechanism is predominant and the overall rate constant of sorption process appears to be controlled by chemical sorption process. The value of sorption energy E = 13 kJ/mol at 298°K and the value of Gibbs free energy ∆G° = 3,222 kJ/mol at 298°K prove that the sorption of strontium on titanium dioxide nanoparticles is an endothermic and non-spontaneous process.

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