n-Pentane isomerization over Pt/WOx/ZrO2 catalysts:: A 1H and 13C NMR study

The skeletal isomerization of n-pentane over platinum-promoted tungstated zirconia has been studied by the H-1 and C-13 nuclear magnetic resonance technique. Pt/WOx/ZrO2 samples with varying Pt concentrations have been used as catalysts. C-13-labeled n-pentane was used to analyze the isotopic label distribution in the reaction products. A few aspects of the mechanism of n-pentane isomerization are discussed. Spectroscopic evidence was obtained indicating that initially n-pentane isomerization proceeds by a monomolecular pathway, most probably on Lewis acid sites, which permit hydride abstraction from n-alkane molecules. At higher conversion degrees, isopentane is produced both mono- and bimolecularly via oligomerization and beta -fission of a chemisorbed C-10-carbenium ion. (C) 2001 Academic Press.