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  • 1
    Electronic Resource
    Electronic Resource
    A study of the oxidative coupling of methane over SrO-La2O3/CaO catalysts by using CO2 as a probe (1995)
    Springer
    Catalysis letters 35 (1995), S. 215-231 
    Details
    ISSN: 1572-879X
    Keywords: oxidative coupling of methane (OCM) ; SrO-La2O3/CaO ; basicity ; CO2-TPD ; carbonates ; in situ FT-IR ; CO2 adspecies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract 20%SrO-20%La2O3/CaO catalyst (SLC-2), prepared by impregnation, has shown 18% CH4 conversion and 80% C2-selectivity for the oxidative coupling of methane (OCM) at 1073–1103 K with CH4∶O2 molar ratio=9∶1 and total flow rate of 100 ml/min. Addition of SrO onto La2O3/CaO (LC) catalyst strengthens the surface basicity and leads to an increase in CH4 conversion and C2-selectivity. Meanwhile, the reaction temperature required to obtain the highest C2-yield increases with increasing SrO content. The formation of carbonate on the catalyst surface is the main reason for the deactivation of LC and SLC catalysts. If the amount of CO2 added into the feed is appropriate and the reaction temperature is high enough, there is no deactivation at all. In such case, the added CO2 will suppress the formation of CO2 produced via the OCM reaction, therefore, improves the C2-selectivity. The FT-IR spectra of CO2 adspecies recorded at different temperatures show that CO2 interacts easily with the catalyst surface to form different carbonate adspecies. Unidentate carbonate is the main CO2 adspecies formed on the catalyst surface. On the LC catalyst surface, the unidentate carbonate was first formed on Ca2+ cations at room temperature. If the temperature is higher than 473 K, it will form on La3+ cations. On the SLC catalyst surface, if the temperature is lower than 573 K, only the unidentate carbonate formed on Ca2+ cations could be observed. When the temperature is higher than 673 K, it will then form on Sr2+ cations. This suggests that the unidentate carbonate can migrate on the LC and SLC catalyst surface on one hand, and on the other hand, that the surface composition of SLC catalysts is dynamic in nature. On the basis of both the decomposition temperatures of the carbonate species, and the temperature dependence of the δΝ value which is the difference of symmetric and asymmetric stretching frequencies of surface carbonates, the in situ FT-IR technique offered two approaches to measure the surface basicity of the SLC catalyst. The results thus obtained are in good agreement with that of CO2-TPD. The role of the surface basicity of the SLC catalyst is also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00807178
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    Paper (German National Licenses)
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  • 2
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    Ice shelf structure derived from dispersion curve analysis of ambient seismic noise, Ross Ice Shelf, Antarctica (2016)
    Oxford University Press
    Details
    Publication Date: 2022-05-26
    Description: Author Posting. © The Author(s), 2016. This article is posted here by permission of The Royal Astronomical Society for personal use, not for redistribution. The definitive version was published in Geophysical Journal International 205 (2016): 785-795, doi:10.1093/gji/ggw036.
    Description: An L-configured, three-component short period seismic array was deployed on the Ross Ice Shelf, Antarctica during November 2014. Polarization analysis of ambient noise data from these stations shows linearly polarized waves for frequency bands between 0.2 and 2 Hz. A spectral peak at about 1.6 Hz is interpreted as the resonance frequency of the water column and is used to estimate the water layer thickness below the ice shelf. The frequency band from 4 to 18 Hz is dominated by Rayleigh and Love waves propagating from the north that, based on daily temporal variations, we conclude were generated by field camp activity. Frequency–slowness plots were calculated using beamforming. Resulting Love and Rayleigh wave dispersion curves were inverted for the shear wave velocity profile within the firn and ice to ∼150 m depth. The derived density profile allows estimation of the pore close-off depth and the firn–air content thickness. Separate inversions of Rayleigh and Love wave dispersion curves give different shear wave velocity profiles within the firn. We attribute this difference to an effective anisotropy due to fine layering. The layered structure of firn, ice, water and the seafloor results in a characteristic dispersion curve below 7 Hz. Forward modelling the observed Rayleigh wave dispersion curves using representative firn, ice, water and sediment structures indicates that Rayleigh waves are observed when wavelengths are long enough to span the distance from the ice shelf surface to the seafloor. The forward modelling shows that analysis of seismic data from an ice shelf provides the possibility of resolving ice shelf thickness, water column thickness and the physical properties of the ice shelf and underlying seafloor using passive-source seismic data.
    Description: PDB, AD and PG were supported by NSF Grant PLR 1246151. RAS was supported by NSF Grant PLR-1246416. DAW, RA and AN were supported under NSF Grants PLR-1142518, 1141916 and 1142126, respectively. PDB also received support from the California Department of Parks and Recreation, Division of Boating and Waterways under contract 11-106-107.
    Keywords: Glaciology ; Surface waves and free oscillations ; Seismic anisotropy ; Antarctica
    Repository Name: Woods Hole Open Access Server
    Type: Article
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