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Isomerization of n-Butane and of n-Pentane in the Presence of Sulfated Zirconia: Formation of Surface Deposits Investigated by In Situ UV-vis Diffuse Reflectance Spectroscopy

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Ahmad,  Rafat
Inorganic Chemistry, Fritz Haber Institute, Max Planck Society;

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Melsheimer,  Jörg
Inorganic Chemistry, Fritz Haber Institute, Max Planck Society;

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Jentoft,  Friederike C.
Inorganic Chemistry, Fritz Haber Institute, Max Planck Society;

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Schlögl,  Robert
Inorganic Chemistry, Fritz Haber Institute, Max Planck Society;

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Citation

Ahmad, R., Melsheimer, J., Jentoft, F. C., & Schlögl, R. (2003). Isomerization of n-Butane and of n-Pentane in the Presence of Sulfated Zirconia: Formation of Surface Deposits Investigated by In Situ UV-vis Diffuse Reflectance Spectroscopy. Journal of Catalysis, 218, 365-374. doi:10.1016/S0021-9517(03)00144-1.


Cite as: http://hdl.handle.net/11858/00-001M-0000-0011-11DE-E
Abstract
Catalytic performance and formation of carbonaceous deposits were studied simultaneously during alkane isomerization over sulfated zirconia in a fixed bed flow reactor with an optical window for in situ UV-vis diffuse reflectance spectroscopy. The reactions of n-butane (5 kPa) at 358 and 378 K and of n-pentane (0.25 kPa) at 298 and 308 K passed within 5 h or less through an induction period, a conversion maximum, and a period of deactivation; a steady activity of 64 and 77 µmol g-1 h-1 (isobutane formation) and 3 µmol g-1 h-1 (isopentane, both temperatures) remained. UV-vis spectra indicate the formation of unsaturated surface deposits; the band positions at 310 nm (n-butane reaction) and 330 nm (n-pentane) are within the range of monoenic allylic cations. More highly conjugated allylic cations (bands at 370 and 430 nm) became evident during n-butane reaction at 523 K. The chronology of events suggests that the surface deposits are (i) a result only of the bimolecular and not the monomolecular reaction mechanism, and (ii) are formed in a competitive reaction to the alkane product