Abstract
The effect of WO
3 (5–50 wt%) and ZnO (0.7–22 wt%) on the catalytic properties of Pt/WO
3/(ZnO)–ZrO
2 for
n-heptane (
n-C
7) hydroisomerization was investigated. The optimized WO
3 and ZnO contents are 20 wt% and 3.4 wt%, respectively. The catalytic performance is achieved at 81%
n-C
7 conversion and 89% C
7 isomer selectivity at 250 °C, which is reproducible and can be kept constant over 82 h under reaction conditions. Both WO
3 and ZnO can stabilize the tetragonal phase of ZrO
2. The Brønsted acid-to-Lewis acid ratio should be optimized to achieve high catalytic performance. The activity for Pt/WO
3/ZrO
2 using Zr(OH)
4 as the catalyst support (
n-C
7 conversion, 88% at 250 °C) is much higher than that for Pt/WO
3/ZrO
2 with ZrO
2 as the support (
n-C
7 conversion, 9% at 250 °C) with the same Pt and WO
3 loadings. BET, SEM-EDX, and pyridine-FTIR analyses show that acid treatment can successfully enhance the surface area (from 73 to 91 m
2/g), increase the number of Brønsted acid sites, and lower the surface Zn:Zr ratio (from 0.43 to 0.15) for ZnO–ZrO
2 with 22 wt% ZnO. The yield of C
7 isomers is increased from nil to 47% at 300 °C on Pt/WO
3/ZnO–ZrO
2 catalyst after acid treatment. It is suggested that
n-heptane hydroisomerization activity is related to acidity, surface area, and crystalline phase of ZrO
2.