Effects of hydrogen on heptane isomerization over zirconium oxide modified with tungsten oxide and platinum
Heptane isomerization was carried out over Pt/WO3-ZrO2 under a hydrogen pressure range 0–2 MPa to elucidate the effects of hydrogen on the activity and selectivity of the catalyst. Optimum catalyst was prepared by calcination of WO3-ZrO2 at 1053 K and loading of 0.75 wt% of Pt with a constant WO3 content of 11 wt%. The rate of isomerization was slightly negative in hydrogen pressure in a high pressure range (>0.3 MPa) and positive in a low pressure range (<0.3 MPa). Cracking was markedly suppressed in the reaction under a high hydrogen pressure, which is caused by a high concentration of hydride ion species on the surface. Hydride ions originating from hydrogen molecules play a key role in selective isomerization of heptane. Hydride transfer step was suggested to be slow as compared to skeletal rearrangement among mono- and di-branched carbenium ion intermediates. By controlling the reaction conditions, a high isomerization selectivity of 94% at a conversion of 80% was obtained at 553 K under a hydrogen pressure of 1.55 MPa.
Graphical abstractHeptane isomerization over Pt/WO3-ZrO3 was studied to elucidate the effects of hydrogen on the activity and selectivity. Selectivity for isomerization is markedly improved with hydrogen pressure. The hydride species originating from hydrogen play an important role in selective formation of isomerized heptanes. A selectivity of 94% at 80% conversion was obtained by controlling catalyst preparation and reaction conditions.Figure optionsDownload full-size imageDownload as PowerPoint slide
Journal: Applied Catalysis A: General - Volume 362, Issues 1–2, 30 June 2009, Pages 75–81