Abstract
The electrical conductivity of titanium and zirconium pyrophosphates used as catalysts in n-butane oxidative dehydrogenation has been measured under oxygen and n-butane at 400 and 500 °C and under subsequent exposures to both gases at the catalytic reaction temperature. The two compounds appeared to be p-type semiconductors under air with positive holes as the main charge carriers but became n-type when contacted with n-butane. If their conductivities are comparable as p-type semiconductors (within one order of magnitude), by contrast, they differ by 3 orders of magnitude when being n-type semiconductors. These results explain the difference in catalytic reaction mechanism encountered on the two solids. The alkane activation was proposed to be related in both cases to the p-type semiconducting properties of the solids, likely through hydrogen abstraction by a surface O- species, forming a C4H9 • radical which will similarly undergo a second hydrogen abstraction to form butenes. The changes in activation energy and in selectivity on TiP2O7 at higher temperatures (>450 C) are indicative of a change in mechanism, possibly with the transient formation of an alkoxide species.
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Marcu, IC., Millet, JM.M. & Herrmann, JM. Semiconductive and Redox Properties of Ti and Zr Pyrophosphate Catalysts (TiP2O7 and ZrP2O7). Consequences for the Oxidative Dehydrogenation of n-Butane. Catalysis Letters 78, 273–279 (2002). https://doi.org/10.1023/A:1014944231515
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DOI: https://doi.org/10.1023/A:1014944231515