The role of platinum in hexane isomerization over Pt/FeOy/WOx/ZrO2

Article abstract of DOI:10.1006/jcat.2001.3229

Hexane isomerization was studied in Pt-free and Pt-containing highly acidic iron oxide/tungsten oxide zirconia (FeO_y/WO_x/ZrO₂) catalysts. Hexane isomerization on WO_x/ZrO₂-based catalysts occurred mainly on monofunctional acid sites via intermolecular hydride transfer reactions between neutral molecules and carbenium ions. The highly acidic character of WO_x/ZrO₂ was such that hexane isomerization did not proceed via the classical dual functional mechanism. These results were consistent with those obtained in strong acid systems, and contrast those of zeolite-based catalysts, where the presence of metal is required to achieve high conversions. The presence of platinum led to a moderately higher level of deuterium exchange in the isohexane products, but a large increase in the deuteration of the normal hexane starting material. At ～ 20% conversion, nearly all of the unreacted normal hexane molecules contain at least one deuterium atom over Pt/FeO_y/WO_x/ZrO₂, while only 4-5% of the hexane was deuterated over Pt-free FeO_y/WO_x/ZrO₂. These results can be attributed to branched isomer exchange with deuterated Broonsted sites, supplemented by non-isomer-selective C-H bond activation by platinum.