Mechanistic study on skeletal isomerization of n-butane using 1,4-13C2-n-butane on typical solid acids and their Pt-promoted bifunctional catalysts

Abstract

Abstract The reaction mechanism of skeletal isomerization of n-butane over typical solid acids such as Cs2.5H0.5PW12O40, sulfated ZrO2, and WO3/ZrO2 and their Pt-promoted catalysts have been studied by the use of 1,4- 13 C 2 -n-butane. Isotopic distributions in product isobutane and reactant n-butane were quantitatively analyzed by field-ionization mass spectrometry (FI-MS). On these solid acids, below 423 K, isobutane consisted of 13 C 0 – 13 C 4 isotopes, whose distributions were close to the corresponding binomial distributions, with the reactant n-butane being mainly 13 C 2 -n-butane. This indicates that the isomerization proceeded with an intermolecular rearrangement through a bimolecular mechanism. In the temperature range of 493–523 K over these solid acids, the isotopic distributions in isobutane deviated from the binomial distributions; the fractions of 13 C 2 -isobutane were greater than those expected from the binomial distributions, showing that an intramolecular (monomolecular) rearrangement became significant. Further, the product isobutane was found to consist of exclusively 13 C 2 -isobutane over these Pt-promoted catalysts in the presence of H2, demonstrating the operation of a monomolecular mechanism on the bifunctional catalysts.