n-Butane conversion on sulfated zirconia:the mechanism of isomerization and ~(13)C-label scrambling as studied by in situ ~(13)C MAS NMR and ex situ GC-MS

摘要

Using ~(13)C MAS NMR,conversion of selectively ~(13)C-labeled n-butane on sulfated zirconia catalyst has been demonstrated to proceed initially via two parallel routes:scrambling of the selective ~(13)C label in the n-butane molecule and selective formation of isobutane.The combination of the results obtained by both in situ ~(13)C MAS NMR and ex situ GC-MS analysis provides evidnece for the monomolecular mechanism of the ~(13)C-label scrambling,whereas isomerization into isobutane proceeds through a pure bimolecular mechanism.Further,the intermolecular mechanism of n-butane isomerization is complicated and turns into conjunct polymerization.Besides isobutane,conjunct polymerization gives also the products of butane disproportionation,propane and pentanes,as well as the stable cyclopentenyl cations;the latter may be in charge of catalyst deactivation.