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  • 1
    Electronic Resource
    Electronic Resource
    Characterization study of GaAs(001) surfaces using ion scattering spectroscopy and x-ray photoelectron spectroscopy (1997)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 6160-6164 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A surface characterization study using ion scattering spectroscopy (ISS) and x-ray photoelectron spectroscopy (XPS) has been performed on solvent cleaned, n-type GaAs(001) substrates before and after cleaning by ion sputtering and annealing. The native oxide layer on this surface contains large amounts of As2O5,As2O3, and Ga2O3 according to XPS with Ga2O3 being the predominant species. Before cleaning C is present as hydrocarbons, carbonates, and carbide with hydrocarbons as the predominant chemical state. Ion sputtering converts the hydrocarbons into carbide, which is difficult to remove by further sputtering/annealing cleaning cycles, but O is removed by these cycles. According to ISS data, the outermost atomic layer is enriched in Ga before cleaning, but after cleaning the ISS Ga-to-As atom ratio is about 1:2. The results obtained in this study are consistent with the presence of a layered oxide structure with Ga2O3 just above the interface. A sputter-cleaned surface initially exhibits an increase in the Ga-to-As surface atom ratio which returns to the initial state with time (∼2 h) as observed by ISS. The Ga-to-As surface atom ratio also increases by annealing at temperatures as low as 180 °C. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.364398
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  • 2
    Electronic Resource
    Electronic Resource
    Formation and detection of subsurface oxygen at polycrystalline Pd surfaces (1996)
    Springer
    Catalysis letters 39 (1996), S. 179-182 
    Details
    ISSN: 1572-879X
    Keywords: subsurface oxygen ; polycrystalline Pd ; ion scattering spectroscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract An ion-sputtered, oxygen-exposed, polycrystalline palladium surface has been studied using ion scattering spectroscopy (ISS) before and after exposures to H2 and CO. A room-temperature exposure to O2 for 1 min at 1 × 10−7 Torr does not yield chemisorbed oxygen in the outermost layer of atoms according to the ISS data. However, subsequent exposure to H2 or CO induces subsurface oxygen formed during the Oa exposure to migrate to the surface under a chemical driving force and populate the outermost atomic layer where it is detected by ISS. This study demonstrates that a reductive treatment can increase the oxygen content of a surface and provides a useful method for examining subsurface oxygen.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00805580
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  • 3
    Electronic Resource
    Electronic Resource
    An efficient catalyst for the production of isobutanol and methanol from syngas. XI. K‐ and Pd‐promoted Zn/Cr/Mn spinel (excess ZnO) (1999)
    Springer
    Catalysis letters 62 (1999), S. 169-173 
    Details
    ISSN: 1572-879X
    Keywords: higher alcohol synthesis ; Cs‐ and Pd‐promoted Zn/Cr/Mn spinel catalysts ; isobutanol ; methanol ; synthesis gas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A 2.25 wt% K‐ and 6.0 wt% Pd‐promoted Zn/Cr/Mn spinel (excess ZnO) higher alcohol synthesis (HAS) catalyst has been tested for the production of isobutanol and methanol at 440°C and 1500 psig. An isobutanol production rate of 179 g kg−1 h−1, a methanol‐to‐isobutanol mole ratio of 1.3 and a total alcohol rate of 304 g kg−1 h− are attained. This ratio is slightly higher than the desired value of 1.0 for MTBE production. These results are superior to others presented in the literature thus far. Surface characterization data indicate that the near‐surface region of the catalyst consists primarily of ZnO and K. Pretreating the catalyst in a reductive environment similar to that given to the catalyst before reaction tests, causes an enrichment of the K promoter at the surface. The product stream composition does not significantly change during five days of testing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019011408962
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  • 4
    Electronic Resource
    Electronic Resource
    An efficient catalyst for the production of isobutanol and methanol from syngas. VIII: Cs- and Pd-promoted Zn/Cr spinel (excess ZnO) (1998)
    Springer
    Catalysis letters 50 (1998), S. 199-203 
    Details
    ISSN: 1572-879X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A Cs- and Pd-promoted Zn/Cr spinel (excess ZnO) higher alcohol synthesis (HAS) catalyst has been tested for the production of isobutanol and methanol. An isobutanol production rate of 170 g/(kg h) and a methanol-to-isobutanol mole ratio of 0.44 are attained at 440°C and 1000 psig. This ratio is lower than the desired value of 1.0 for MTBE production. Operating the reactor at a higher pressure of 1500 psig results in a lower isobutanol production rate of 161 g/(kg h) and an increased alcohol ratio of 0.7. A methanol-to-isobutanol mole ratio of 0.75 is also achieved under these operating conditions. These results are superior to others presented in the literature thus far. Surface characterization data indicate that the near-surface region of the catalyst consists primarily of ZnO and Cs. Pretreating the catalyst in a reductive environment similar to that given to the catalyst before reaction tests, causes an enrichment of the Cs promoter at the surface. The product stream composition does not significantly change after 5 days of testing. During this time, however, the amount of Cs relative to Zn measured by XPS at the surface decreases possibly by agglomeration. The Zn remains in a ZnO state after the reductive pretreatment and after removal from the reactor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1019031522089
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  • 5
    Electronic Resource
    Electronic Resource
    Reaction and surface characterization study of Zn/Cr-based higher-alcohol synthesis catalysts X: Effects of excess promoter loading on surface chemistry (1999)
    Springer
    Reaction kinetics and catalysis letters 67 (1999), S. 225-232 
    Details
    ISSN: 1588-2837
    Keywords: K-promoted Zn/Cr spinel catalysts ; higher alcohol synthesis ; isobutanol ; methanol ; synthesis gas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Promoter loading level significantly affects the catalytic behavior of Zn/Cr spinel higher alcohol synthesis (HAS) catalysts. In this study a 5.9 wt.% Pd-promoted Zn/Cr spinel with a 5 and 7 wt.% K promoter have been tested and compared. At 1500 psig and 400°C, the catalyst containing 5 wt.% K results in the production of slightly more butanol, less methanol and more hydrocarbons. Using ion scattering spectroscopy and X-ray photoelectron spectroscopy, differences are found between the two catalyst surfaces which must be responsible for the differences in catalytic behavior.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02475764
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  • 6
    Electronic Resource
    Electronic Resource
    Catalytic Methane Oxidation Over Pd Supported on Nanocrystalline and Polycrystalline TiO2 Mn3O4, CeO2 and ZrO2 (2000)
    Springer
    Reaction kinetics and catalysis letters 70 (2000), S. 97-103 
    Details
    ISSN: 1588-2837
    Keywords: Catalytic methane oxidation ; oxide-supported palladium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The catalytic oxidation of methane has been examined over Pd supported on nanocrystalline (n-) and polycrystalline (p-) TiO2, Mn3O4, CeO2 and ZrO2. In all cases the Pd supported on the nanocrystalline oxides performs better on a mass basis than Pd supported on the polycrystalline oxides. Conversion vs temperature curves indicate that n-ZrO2 is more active than p-ZrO2 and that calcining both n-ZrO2 and p-ZrO2 at 500°C produces better catalysts than calcining at 280°C. n-CeO2 is a very good catalysts for methane oxidation, while p-CeO2 is not, and Pd supported on n-CeO2 performs much better than bare n-CeO2 and somewhat better than Pd supported on p-CeO2; Pd supported on n-Mn3O4 or p-Mn3O4 does not perform as well as CeO2-supported Pd catalysts. The 5 wt.% Pd/n-ZrO2 catalyst calcined at 500°C performs very well, achieving 100% conversion at 320°C for the reactor conditions used, while 5 wt.% Pd/n-CeO2 exhibits initial activity at the lowest temperature of about 100°C. The best catalyst tested in this study is 30 wt.% Pd/n-TiO2, which achieves 100% conversion at 300°C.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1010362632223
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