Adjacent Pt Nanoparticles and Sub-nanometer WOx Clusters Determine Catalytic Isomerization of C7H16

Abstract

Processes for the isomerization of light alkanes have been commercialized; however, the isomerization of paraffins (CnH2n+2, n ≥ 7) remains a challenge. On mesoporous tungsten-zirconia catalyst supported Pt catalysts (Pt/WZrOx), initial isomerization productivity of 5249 moli-C7/molPt/h was obtained for n-heptane reforming at 275 °C and 5 bar of hydrogen. The catalyst possessed quasi-monolayer and uniformly distributed WOx clusters (diameter of ∼0.5 nm), and Pt nanoparticles were preferentially deposited in close vicinity to these WOx sub-nanometer monolayers. The initial productivity over the best Pt/WZrOx catalyst was 18 times higher than that of a corresponding physical mixture (0.8 wt % Pt/ZrO2 + WZrOx), highlighting the significance of intimacy between the Pt and WOx species. The isomerization could not be triggered until the acid density of the catalysts reached a threshold because of the necessity of close proximity between adequate acid sites and adjacent Pt metal sites. Meanwhile, the adjacency increased the metallicity of the supported Pt; thus, enabling easier activation of C–H bonds of C7H16.(Figure presented).