The gamma-ray induced chemisorption of oxygen on perovskite type catalysts: determination by reduction with hydrazine sulphate/hydroxylamine hydrochloride
01 Nov 1986-Journal of Radioanalytical and Nuclear Chemistry (Akadémiai Kiadó, co-published with Springer Science+Business Media B.V., Formerly Kluwer Academic Publishers B.V.)-Vol. 107, Iss: 4, pp 225-238
TL;DR: In this article, the authors measured the amount of chemisorbed oxygen in gaseous N2/N2O liberated by treatment with hydrazine sulphate/hydroxylamine hydrochloride.
Abstract: Chemisorbed oxygen can be determined quantitatively by the measurement of gaseous N2/N2O liberated by treatment with hydrazine sulphate/hydroxylamine hydrochloride. The amount of chemisorbed oxygen depends on the degree of dispersion during irradiation and also the γ-dose. The chemisorption is enhanced in the presence of moisture. The partial reduction of the transition metal ion favours the formation of chemisorbed oxygen.
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TL;DR: In this article, post annealing introduced oxygen vacancy is proposed to play critical roles in tuning the photoluminescence (PL) of Eu2+ and Eu3+ co-doped SrSO4 microcrystals.
Abstract: Eu2+ and Eu3+ co-doped SrSO4 microcrystals were synthesized by employing Eu3+ as the sole doping source in the precipitation synthesis. As the annealing temperature increases from 200 to 1000 °C, it is found that the broad photoluminescence (PL) band of Eu2+ peaking at 378 nm is dramatically enhanced in intensity as the cost of the narrowband emissions of Eu3+ at 584, 591 and 612 nm, respectively. Moreover, Two broad PL bands, one of which is centered at 500 nm while the other is centered at 625 nm, are recorded upon post annealing. On the basis of density functional calculations, post annealing introduced oxygen vacancy is proposed to play critical roles in tuning the PL of Eu2+ and Eu3+ co-doped SrSO4. On one hand, the oxygen vacancy is responsible for the enhanced emission of Eu2+ at 378 nm by reducing Eu3+ to Eu2+. On the other hand, the oxygen vacancy acts as electron trap and luminescence center in SrSO4 with the result of the broad PL band centered at 500 nm. Our results have demonstrated that the PL of Eu2+ and Eu3+ co-doped SrSO4 microcrystals can be tuned by simply varying the post annealing temperature.
18 citations
TL;DR: In this paper, a qualitative molecular orbital model has been proposed for the chemisorption of superoxide ion (O2−) on the reduced transition metal centers (Ni2+).
Abstract: Electronspin resonance (ESR) studies of γ-irradiated LaNiO3 revealed the formation of chemisorbed superoxide ion (O2−) and F centers (electrons trapped in anion vacancies). X-ray photoelectron spectroscopy (XPS) showed that the γ-irradiation of LaNiO3 in the presence of moisture leads to the reduction of the transition metal (Ni3+ to Ni2+) which in turn facilitates the formation of O2− and surface carbonate species (CO32−). A qualitative molecular orbital model has been proposed for the chemisorption of O2− on the reduced transition metal centers (Ni2+). The hydrated electron generated by the radiolysis of moisture reduces the transition metal. Gamma-irradiated LaNiO3 shows enhanced catalytic activity for the decomposition of hydrogen peroxide (H2O2) and the increase in catalytic activity is attributed to the reduced metal content. The formation of chemisorbed oxygen decreases the electrical conductivity by trapping the charge carriers.
2 citations
TL;DR: In this article, a qualitative molecular orbital model has been proposed for the chemisorption of O 2 − on the reduced transition metal centers (Mn2+), which in turn leads to the formation of superoxide ions and surface carbonate species (CO 3 2− ).
Abstract: Catalysis of mixed oxide LaMnO3 was studied for the decomposition of hydrogen peroxide (H2O2). The catalyst was γ-irradiated in open petri dishes, vacuum, dry oxygen and moist oxygen. LaMnO3 irradiated in moist oxygen showed highest catalytic activity. X-ray photoelectron spectroscopic (XPS) studies were carried out to investigate the surface modifications occurred during γ-irradiaiton of LaMnO3. No significant change in the surface was noticed in LaMnO3 irradiated in vacuum and dry oxygen. However, LaMnO3 irradiated in moist oxygen and in open petri dishes showed the reduction of transition metal (MN3+ to Mn2+) which in turn leads to the formation of chemisorbed superoxide ions (O 2 − ) and surface carbonate species (CO 3 2− ). The latter processes decreases the electrical conductivity by trapping the charge carriers. The hydrated electron generated by the radiolysis of moisture reduces the transition metal. A qualitative molecular orbital model has been proposed for the chemisorption of O 2 − on the reduced transition metal centers (Mn2+).
1 citations
TL;DR: The influence of γ-radiation on LaCoO3 for the catalytic decomposition of H2O2 has been studied in this paper, where the enhancement in catalytic activity was found to be directly proportional to the reduced metal content.
Abstract: The influence of γ-radiation on LaCoO3, for the catalytic decomposition of H2O2 has been studied. ESR and XPS studies of γ-irradiated LaCoO3, snowed, the formation of chemisorbed oxygen (O2) and reduction of Co2+ to Co . γ-irradia]:ion of LaCoO3. causes a decrease in electrical conductivity due to the trapping of charge carriers by the chemisorbed oxygen. SEM photographs of the Y-irradiated sample pellets reveal surface cracks and surface corrosion due to the diffusion of transition metal to surface. The enhancement in the catalytic activity for the decomposition of H2O2 is found to be directly proportional to the reduced metal content.
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TL;DR: It is anticipated that perovskite oxides, appropriately formulated, will show catalytic activity for a large variety of chemical conversions, which makes these oxides attractive models in the study of catalytic chemical conversion.
Abstract: In a time of growing need for catalysts, perovskites have been rediscovered as a family of catalysts of such great diversity that a broad spectrum of scientific disciplines have been brought to bear in their study and application. Because of the wide range of ions and valences which this simple structure can accommodate, the perovskites lend themselves to chemical tailoring. It is relatively simple to synthesize perovskites because of the flexibility of the structure to diverse chemistry. Many of the techniques of ceramic powder preparation are applicable to perovskite catalysts. In their own right, they are therefore of interest as a model system for the correlation of solid-state parameters and catalytic mechanisms. Such correlations [See figure in the PDF file] have recently been found between the rate and selectivity of oxidation-reduction reactions and the thermodynamic and electronic parameters of the solid. For commercial processes such as those mentioned in the introduction, perovskite catalysts have not yet proven to be practical. Much of the initial interest in these catalysts related to their use in automobile exhaust control. Current interest in this field centers on noble metalsubstituted perovskites resistant to S poisoning for single-bed, dual-bed, and three-way catalyst configurations. The formulations commercially tested to date have shown considerable promise, but long-term stability has not yet been achieved. A very large fraction of the elements that make up presently used commercial catalysts can be incorporated in the structure of perovskite oxides. Conversely, it is anticipated that perovskite oxides, appropriately formulated, will show catalytic activity for a large variety of chemical conversions. Even though this expectation is by no means a prediction of commercial success in the face of competition by existing catalyst systems, it makes these oxides attractive models in the study of catalytic chemical conversion. By appropriate formulation many desirable properties can be tailored, including the valence state of transition metal ions, the binding energy and diffusion of O in the lattice, the distance between active sites, and the magnetic and conductive properties of the solid. Only a very small fraction of possible perovskite formulations have been explored as catalysts. It is expected that further investigation will greatly expand the scope of perovskite catalysis, extend the understanding of solid-state parameters in catalysis, and contribute to the development of practical catalytic processes.
461 citations
TL;DR: In this article, a trivalent version of LaNi03, containing nickel (II) oxide, was prepared and its structure studied by X-ray diffraction methods, and all the lines of the diffraction patterns out to 2 theta = 75 degrees could be indexed satisfactorily on the basis of a monoclinic unit cell with a = 3.92 A.
Abstract: : LaNi03, containing nickel in the trivalent state was prepared and its structure studied by X-ray diffraction methods. The dimensions of the rhombohedral pseudo-cell are a = 7.676=0.002 A., alpha = 90 degrees 43 minutes. The dimensions of the primitive rhombohedral cell are alpha sub p = 60 degrees 49 minutes, a = 5.461 A. The hexagonal form of this cell has the following dimensions: a = 5.456 A., c = 13.122 A. Neodymium oxide reacts with nickel (II) oxide, in the presence of sodium carbonate, to form a single phase whose composition may vary between Nd 1.67Ni(+2) 0.72Ni(+3) 0.41 03.84 and Nd 1.75Ni(+2) 0.57 Ni(+3) 0.43 03.84. An increase in the ratio Nd:Ni results in the formation of more trivalent nickel. With the exception of one very weak line at 2 theta = 31. 2 degrees, all the lines of the X-ray diffraction patterns out to 2 theta = 75 degrees could be indexed satisfactorily on the basis of a monoclinic unit cell with a = 3.92 A., b = 6.16 A., c = 3.77 A. and beta = 92.4 degrees. Samarium, gadolinium and yttrium oxides do not appear to form stable compounds with nickel (II) oxide under the conditions used to form the other rare earth nickel oxides. The product of reaction between lanthanum oxide, samarium oxide and nickel (II) oxide, in the mole ratio 1:1.4, was a new phase which seemed to be isomorphous with the phase obtained from the reaction of mixtures having compositions between 2Ni0.1.5Nd203 and 2Ni0.1.75Nd203.
133 citations
TL;DR: In this article, rare earth orthoferrites and the analogous cobalt compounds can be prepared by the thermal decomposition of the appropriate rare earth ferricyanide or cobalticyanide compound, e.g., LaFe(CN)6·XH2O.
Abstract: Rare earth orthoferrites and the analogous cobalt compounds can be prepared by the thermal decomposition of the appropriate rare earth ferricyanide or cobalticyanide compound, e.g., LaFe(CN)6·XH2O. These compounds are readily precipitated from aqueous solution and since the excess of either component remains in solution there is precise control of stoichiometry. Similarly, the ferrocyanide compounds, NH4 R.E. Fe(CN)6·XH2O may be utilized. Because the mixing is on an atomic scale, the desired compound is achieved by a single relatively low temperature calcination and without any subsequent milling or contamination.
88 citations