Browsing by Subject "Reaction mechanism"

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    Bi2O3 and BiOCl electrospun nanosheets and morphology-dependent photocatalytic properties
    (Royal Society of Chemistry, 2014) Babu, V. J.; Bhavatharini, R. S. R.; Ramakrishna, S.
    BiOCl and Bi2O3 nanosheet like structures were produced by electrospinning. The morphological changes were observed by changing precursor (BiOCl3 and Bi(NO3)3·5H 2O) concentrations. These nanosheets were analyzed by XRD, which reveals that the crystal structures of BiOCl and Bi2O3 belonged to tetragonal and beta-phase systems respectively. Both nanostructures were employed for the photodegradation of Alizarin Red S (ARS) dye under UV light (<390 nm) irradiation. BiOCl nanosheet like structures exhibited superior photocatalytic activity (PCA) for the degradation of ARS dye and their half-life was estimated from the kinetic plots of PCA. A plausible reaction mechanism is proposed for the PCA and discussed in detail. © the Partner Organisations 2014.
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    Characterization of niobium-zirconium mixed oxide as a novel catalyst for selective catalytic reduction of NO x
    (2009) Cayirtepe, I.; Naydenov, A.; Ivanov, G.; Kantcheva, M.
    The performance of mixed niobium-zirconium oxide in the SCR of NO x with propene in excess oxygen has been studied. The mixed oxide is prepared by impregnation of hydrated zirconia with acidic solution (pH 0.5) of peroxoniobium(V) complex, [Nb2(O2)3] 4+, ensuring ZrO2:Nb2O5 mole ratio of 6:1. The calcined sample (denoted as 25NbZ-P) has the structure of Zr 6Nb2O17. According to the catalytic test, the conversion of NO x over the 25NbZ-P catalyst passes through a maximum at 220 °C. Based on the in situ FT-IR results, a reaction mechanism is proposed with nitroacetone and NCO species as the key reaction intermediates. The results of the investigation show that the catalytic properties of the Zr6Nb2O17 solid solution could be of interest regarding the development of low-temperature catalyst for the SCR of NO x with hydrocarbons. © 2009 Springer Science+Business Media, LLC.
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    Preparation and characterization of niobia-containing solid acid
    (2010) Çayırtepe, İlknur
    The research in this work is directed towards (i) the development of effective methods for synthesis of new solid acids based on zirconia and niobia resulting in high concentration of acid sites and (ii) investigation of the potential of these materials as catalysts for the selective catalytic reduction (SCR) of nitrogen oxides (NOx) with hydrocarbons and alcohol transformations. A series of NbOx/ZrO2 and WOx/Nb2O5 samples have been obtained by the so called “peroxo route” using acidic H2O2 solutions as a reaction medium. The impregnation of hydrated zirconia with solutions of [Nb2(O2)3] 4+ ions allows the synthesis of Nb2O5-ZrO2 samples with niobium loading up to 30 wt % without formation of a seperate Nb2O5 phase. The presence of a single phase of Zr6Nb2O17 has been observed for the sample containing 25 wt% of Nb. The formation of Zr6Nb2O17 is favored by the partial solubility of hydrated zirconia in the H2O2 solution. Among the fully crystallized Nb2O5-based samples, the solid WO3-Nb2O5 solution containing 20 wt % of WO3 has the highest and strongest Brønsted acidity. Catalytic activity tests for the C3H6-SCR of NOx have shown that Pd-free and Pdpromoted niobia-based samples containing 20 wt% WO3 are inactive, whereas the Zr6Nb2O17 and 0.1Pd/ Zr6Nb2O17 samples catalyze this reaction. The conversion of NOx in the SCR of NOx with propene in excess oxygen over Zr6Nb2O17 passes through a maximum at 493 K. The mixed oxide displays good water tolerance and resistance toward SO2 poisoning. Based on the in situ FT-IR results, a reaction mechanism is proposed with nitroacetone and NCO species as the key reaction intermediates. The results of the investigation show that the catalytic properties of the new solid acid Zr6Nb2O17 could be of interest regarding the development of sulfur- and water-tolerant, low-temperature catalysts for the SCR of NOx with hydrocarbons. The Zr6Nb2O17 and Nb2O5-containing 20 % WO3 samples have potential as lowtemperature catalysts for oxidant-free or oxidative transformation of alcohols, respectively.