n-Heptane Hydroisomerization over Alumina Binder-Shaped Pt-WO₃/ZrO₂/Al₂O₃ Catalysts

A series of Pt-WO₃/ZrO₂/Al₂O₃(PtWZA)catalysts were prepared by extrusion method using Al₂O₃ as a binder. The isomerization performance of n-heptane by PtWZA catalysts was evaluated on a micro-fixed bed reactor. The influence of Al₂O₃ mass fraction, WO₃ mass fraction and calcination temperature on the physico-chemical properties and isomerization performance of PtWZA_catalysts were studied. The crystalline structure, specific surface area and acidity of catalysts were determined by XRD、nitrogen adsorption-desorption and Py-FTIR, respectively. The results indicated that the addition of proper amount of Al₂O₃ had a significant effect on the isomerization performance for PtWZA catalysts. However, the effect of the catalytic performance on the isomerisation activity is not only related to the mass fraction of Al₂O₃, but also to the mass fraction of WO₃. The catalytic activity was greatly enhanced when small mass fraction (2%) of Al₂O₃ was introduced into PtWZA catalysts for a low mass fraction (15%) of WO₃. However, the catalytic activity increased slightly when small amount of Al₂O₃ was introduced into Pt20WZ catalysts. The n-heptane isomerization activity of Pt15WZA and Pt20WZA catalysts greatly decreased with 15% Al₂O₃ mass fraction. The isomerization activity of PtWZ15A catalysts increased significantly when the mass fraction of WO₃ increased. The enhancement in the calcination temperature led to an appreciable improvement in the catalytic activity of Pt20WZ10A catalysts. High calcination temperature resulted in the decrease of isomerisation activity. The suitable calcination temperature of Pt20WZ10A catalysts is in the range of 800-850℃.