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P. C. Schmidt - One of the best experts on this subject based on the ideXlab platform.
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Model of work function of tungsten cathodes with Barium Oxide coating
Journal of Applied Physics, 2004Co-Authors: K. C. Mishra, R. Garner, P. C. SchmidtAbstract:Using a full-potential band structure approach, we have investigated the work function of Barium Oxide coated tungsten cathodes in low pressure discharge lamps. The main objective of this work is to understand why the work function for such cathodes is lower than that of the uncoated tungsten. The model studied in this work is based on a well known supposition that the source of thermionic electrons is the Barium atoms released from the Barium Oxide coating due to a chemical reaction with the underlying metallic tungsten. For the unrelaxed seven-layer model of (100) surface of Barium on Barium Oxide, the work function is calculated to be 2.22 eV, which is lower than that of BaO, Ba, and W metals separately. For a fully relaxed nine-layer surface, it becomes 1.36 eV. Although this value of the work function is lower than those estimated for the fluorescent cathodes by electrical measurements, which averages contributions from surfaces in all possible random orientations, this model provides a satisfactory ...
Jack H. Lunsford - One of the best experts on this subject based on the ideXlab platform.
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NO2 Storage and Reduction in Barium Oxide Supported on Magnesium Oxide Studied by in Situ Raman Spectroscopy
The Journal of Physical Chemistry B, 2003Co-Authors: Christian Hess, Jack H. LunsfordAbstract:The mechanism for NO2 storage in Barium Oxide supported on magnesium Oxide (BaO/MgO) was investigated. In situ Raman spectroscopy and XRD were used to follow temporal changes in the composition of the storage material that occurred during the storage process, i.e., during the reaction of 14 mol % BaO with NO2 and NO2/O2, and the reduction of the stored NO2 with CO. Above 200 °C, the interaction of BaO with NO2 leads to both the formation of nitrate and nitrite ions, which, up to 400 °C, occurs via an intermediate Barium−nitro species. At lower loadings (7 mol %), a destabilization of the Barium−nitro species but an enhanced rate for nitrate formation is observed. Similarly, the presence of oxygen enhances the rate for nitrate formation, but suppresses the formation of nitro species. CO reduces the stored NO2 only above 500 °C and leads to the formation of thermally stable carbonates. In the presence of NO2, however, they are displaced during the formation of nitrates at 400 °C.
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Mechanism for NO2 Storage in Barium Oxide Supported on Magnesium Oxide Studied by in Situ Raman Spectroscopy
The Journal of Physical Chemistry B, 2002Co-Authors: Christian Hess, Jack H. LunsfordAbstract:The mechanism for NO2 storage in Barium Oxide supported on magnesium Oxide (BaO/MgO) was investigated. In situ Raman spectroscopy was used to follow temporal changes in the composition of the catalyst that occurred during the reaction with NO2. Up to catalyst temperatures of 400 °C, the formation of an intermediate Barium−nitro phase precedes the formation of nitrate ions, which upon further exposure lead to the formation of bulk nitrates. In contrast, preoxidation of the catalyst or exposure to oxygen leads to the formation of perOxides that enhance the rate for nitrate formation while the formation of nitro species is suppressed above 300 °C. The spectroscopic results are in agreement with a reaction mechanism that has recently been proposed by Broquist et al. (J. Phys. Chem. B 2002, 106, 137) on the basis of DFT calculations.
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A catalytic and in situ Raman spectroscopy study of the decomposition of nitrous Oxide over Barium Oxide supported on magnesium Oxide
Applied Catalysis A-general, 1999Co-Authors: Shuibo Xie, Jack H. LunsfordAbstract:Abstract The decomposition of N 2 O in a 10% N 2 O/He mixture occurs at a rate of 0.8 μmol g −1 s −1 at 500°C over a catalyst containing 14 mol% BaO on MgO (Ba/MgO). Barium Oxide is the active component. The reaction is inhibited by O 2 , via the formation of surface Barium perOxide ions. The decrease in activity due to inhibition of O 2 and the increase in both surface and crystalline BaO 2 were followed in several transient experiments. The variation in perOxide concentrations was determined under catalytic conditions using Raman spectroscopy. The transient results are consistent with a mechanism in which N 2 O reacts with surface Oxide ions to form perOxide ions. At steady state, the surface perOxide ions are nearly in equilibrium with gas phase O 2 . The equilibrium favors extensive decomposition of the perOxide ions to O 2 and surface Oxide ions under the conditions of the catalytic reaction.
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Decomposition of Nitric Oxide over Barium Oxide Supported on Magnesium Oxide. 1. Catalytic Results and in Situ Raman Spectroscopic Evidence for a Barium−Nitro Intermediate
Journal of the American Chemical Society, 1997Co-Authors: Shuibo Xie, Gerhard Mestl, Michael P. Rosynek, Jack H. LunsfordAbstract:Barium Oxide supported on magnesium Oxide (Ba/MgO) exhibits unusual behavior as a catalyst for NO decomposition at Ba loadings of 11 mol % or greater. The catalytic activity is characterized by a sharp decrease in activity when the reaction temperature exceeds a certain value that depends on the partial pressures of NO and O2. The fall-off temperatures are between 630 and 700 °C for concentrations between 1% and 4% NO in helium. At 700 °C with 4% NO, the N2 formation rate was 2.5 μmol g-1 s-1 for a 14 mol % Ba/MgO catalyst. The discontinuity in activity is accompanied by an abrupt change in activation energy for the reaction, which suggests a change in mechanism. In situ Raman spectroscopy was used to follow temporal changes in the composition of the catalyst that occurred after step changes in temperature or NO concentration. A comparison of spectroscopic and catalytic results indicates that a Barium−nitro phase is an intermediate in the catalytic cycle below the fall-off temperature. Nitro species at th...
K. C. Mishra - One of the best experts on this subject based on the ideXlab platform.
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Model of work function of tungsten cathodes with Barium Oxide coating
Journal of Applied Physics, 2004Co-Authors: K. C. Mishra, R. Garner, P. C. SchmidtAbstract:Using a full-potential band structure approach, we have investigated the work function of Barium Oxide coated tungsten cathodes in low pressure discharge lamps. The main objective of this work is to understand why the work function for such cathodes is lower than that of the uncoated tungsten. The model studied in this work is based on a well known supposition that the source of thermionic electrons is the Barium atoms released from the Barium Oxide coating due to a chemical reaction with the underlying metallic tungsten. For the unrelaxed seven-layer model of (100) surface of Barium on Barium Oxide, the work function is calculated to be 2.22 eV, which is lower than that of BaO, Ba, and W metals separately. For a fully relaxed nine-layer surface, it becomes 1.36 eV. Although this value of the work function is lower than those estimated for the fluorescent cathodes by electrical measurements, which averages contributions from surfaces in all possible random orientations, this model provides a satisfactory ...
Michael J. Patterson - One of the best experts on this subject based on the ideXlab platform.
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the storage of nitrogen Oxides on alumina supported Barium Oxide
Catalysis Today, 2002Co-Authors: Noel W. Cant, Michael J. PattersonAbstract:The storage and release of NO 2 on alumina-supported Barium Oxide has been studied with particular attention to the stoichiometry of the two processes. At 400 °C the storage process is characterised by a short period of complete uptake, possibly as nitrito or nitro species, followed by a slower partial uptake in which approximately one NO is released for every three NO 2 lost. The latter reaction appears to supply the oxygen necessary to store NO 2 as nitrate ions. Molecular O 2 has little direct involvement even if in large excess. The second storage reaction also occurs, but to a much lesser extent, with Al 2 O 3 alone. During temperature programmed desorption, release of NO x from Al 2 O 3 peaks at 430°C with evolution of NO 2 and some O 2 . Release from BaO/Al 2 O 3 exhibits an additional peak near 520 °C corresponding to formation of NO and a higher O 2 concentration. The NO may arise from NO 2 since BaO/Al 2 O 3 has activity for NO 2 decomposition by 500°C. Although CO 2 at low concentration is rapidly taken up by BaO/Al 2 O 3 at 400 °C it is displaced by NO 2 and does not interfere with storage. Thermodynamic calculations show that the formation of Ba(NO 3 ) 2 by the reaction of NO 2 with bulk BaCO 3 under the conditions used here is more favourable above 380 °C if NO is evolved than if O 2 is consumed.
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The storage of nitrogen Oxides on alumina-supported Barium Oxide
Catalysis Today, 2002Co-Authors: Noel W. Cant, Michael J. PattersonAbstract:The storage and release of NO₂ on alumina-supported Barium Oxide has been studied with particular attention to the stoichiometry of the two processes. At 400 °C the storage process is characterised by a short period of complete uptake, possibly as nitrito or nitro species, followed by a slower partial uptake in which approximately one NO is released for every three NO₂ lost. The latter reaction appears to supply the oxygen necessary to store NO₂ as nitrate ions. Molecular O₂ has little direct involvement even if in large excess. The second storage reaction also occurs, but to a much lesser extent, with Al₂O₃ alone. During temperature programmed desorption, release of NOₓ from Al₂O₃ peaks at ~430 °C with evolution of NO₂ and some O₂. Release from BaO/Al₂O₃ exhibits an additional peak near 520 °C corresponding to formation of NO and a higher O₂ concentration. The NO may arise from NO₂ since BaO/Al₂O₃ has activity for NO₂ decomposition by 500 °C. Although CO₂ at low concentration is rapidly taken up by BaO/Al₂O₃ at 400 °C it is displaced by NO₂ and does not interfere with storage. Thermodynamic calculations show that the formation of Ba(NO₃)₂ by the reaction of NO₂ with bulk BaCO₃ under the conditions used here is more favourable above 380 °C if NO is evolved than if O₂ is consumed.8 page(s
Gon Seo - One of the best experts on this subject based on the ideXlab platform.
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Deactivation of Barium Oxide-based NOx storage and reduction catalyst by hydrothermal treatment
Korean Journal of Chemical Engineering, 2008Co-Authors: Ji Won Park, Min Park, Hyun-sik Han, Young San Yoo, Gon SeoAbstract:The deactivation of a Barium Oxide-based NO x storage and reduction (NSR) catalyst with hydrothermal treatment was studied by treating it with 10 vol% water vapor diluted in nitrogen at 850°C. XRD, XPS, SEM, IR of CO adsorption, and the N2 adsorption was used to investigate the physical and chemical changes of the NSR catalyst caused by the hydrothermal treatment. The 12 h hydrothermal treatment decreased its NO2 storage capacity by 20%. However, the hydrothermal treatment significantly decreased its ability to reduce the stored NO2. The formation of an inactive phase consisting of platinum and aluminum is believed to be the cause of the severe deactivation of the NSR catalyst.
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Storage of NO2 on potassium Oxide co-loaded with Barium Oxide for NOx storage and reduction (NSR) catalysts
Journal of Molecular Catalysis A-chemical, 2007Co-Authors: Min Park, Ji Won Park, Hyun-sik Han, Gon SeoAbstract:Abstract Barium Oxide-based NO x storage and reduction (NSR) catalysts with different amounts of potassium Oxide were prepared to investigate the role of potassium Oxide in the aspects of amount and strength of NO 2 storage. The dispersion of Barium and potassium Oxides on alumina, the amount and state of NO 2 stored on them, and the desorption profiles of NO 2 from them were examined by XRD, N 2 adsorption, electrical conductivity measurement, XPS, FT-IR and TPD techniques. Barium and potassium Oxides were mainly loaded in the mesopores of the alumina and the NO 2 was stored by being converted to nitrates. The alumina itself had a small capacity for NO 2 storage, but the impregnation with potassium Oxide increased the capacity. The co-loading of potassium Oxide and Barium Oxide enhances the strength of the interaction between the storage material and NO 2 , shifting the desorption peak of NO 2 to a elevated temperature.