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Journal of Thermal Analysis and Calorimetry
Authors:
Maria Crişan
,
Ana Brăileanu
,
D. Crişan
,
Mălina Răileanu
,
N. Drăgan
,
Diana Mardare
,
V. Teodorescu
,
Adelina Ianculescu
,
Ruxandra Bîrjega
, and
M. Dumitru

Abstract  

Among the great number of sol-gel materials prepared, TiO2 holds one of the most important places due to its photocatalytic properties, both in the case of powders and coatings. Impurity doping is one of the typical approaches to extend the spectral response of a wide band gap semiconductor to visible light. This work has studied some un-doped and Pd-doped sol-gel TiO2 nanopowders, presenting various surface morphologies and structures. The obtained powders have been embedded in vitreous TiO2 matrices and the corresponding coatings have been prepared by dipping procedure, on glass substrates. The relationship between the synthesis conditions and the properties of titania nanosized materials, such as thermal stability, phase composition, crystallinity, morphology and size of particles, and the influence of dopant was investigated. The influence of Pd on TiO2 crystallization both for supported and unsupported materials was studied (lattice parameters, crystallite sizes, internal strains). The hydrophilic properties of the films were also connected with their structure, composition and surface morphology. The methods used for the characterization of the materials have been: simultaneous thermogravimetry and differential thermal analysis, powder X-ray diffraction, electron microscopy (TEM, SAED) and AFM.

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Reaction Kinetics, Mechanisms and Catalysis
Authors:
Viorel Chihaia
,
Karl Sohlberg
,
Rodica Zăvoianu
,
Anca Cruceanu
,
Octavian Dumitru Pavel
,
Emilian Angelescu
,
Ana Paula Soares Dias
, and
Ruxandra Bîrjega

Abstract

This contribution presents several aspects concerning the production and characterization of hydrotalcite-like compounds containing Mo-species in the interlayer region (Mo-HT), the corresponding derived mixed oxides (Mo-CHT) and their catalytic activity in the demercaptanization of gasoline contaminated by tert-butanethiol. Mo-HT samples were obtained using two different molybdenum sources, e.g. Na2MoO4 or (NH4)6Mo7O24 and two preparation procedures: (i) ionic exchange and (ii) coprecipitation at pH 10 under high supersaturation. The derived mixed oxides were obtained by calcination at 450 °C during 24 h. The solids have been characterized by chemical analysis, TG/DTA, XRD, SEM–EDX, FTIR, DR-UV–Vis and Raman spectroscopy as well as determination of base sites. The specific area of the solids was determined using the BET method. The best catalysts were found to be those containing higher amounts of Mo species with tetrahedral coordination obtained by calcination of the Mo-HT precursors prepared at pH 10, either by ionic exchange or by co-precipitation using Na2MoO4 as a molybdenum source. Meanwhile, the catalysts containing mainly octahedrally coordinated Mo species (obtained from Mo-HT prepared at pH 10 using (NH4)6Mo7O24·6H2O as molybdenum source) were characterized by a higher concentration of molybdenum species with octahedral coordination, lower number of base sites, smaller surface area, and a poor catalytic activity.

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