Study Of N-Heptane Isomerization Over WO₃-ZrO₂ Solid Superacid

Recently, solid superacid catalysts, e.g. WO₃/ZrO₂,SO₄^2- /ZrO₂,have attractedmuch attention of the researchers, due to their strong acidity, thermal stability,environmentally friendly and excellent catalytic activity.In this study, the WO₃-ZrO₂ support and the M/WO₃-ZrO₂ (M = Pd, Ni)catalyst were prepared by coprecipitation and impregnation methods, respectively.The effects of W content, calcination temperature, drying method on thephysicochemical properties of the M/WO₃-ZrO₂ catalysts were investigated andthe activity of n-heptane isomerization over the M/WO₃-ZrO₂ catalyst was studied.The research results can be concluded as below.For the Pd/WO₃-ZrO₂ catalyst, the formation of the tetragonal ZrO₂ crystallinephase, as well as the WO₃ dispersivity on ZrO₂, was dependent on the W contentand calcination temperature. When a large fraction of the tetragonal ZrO₂ phaseand the WO₃ monolayer on ZrO₂ formed, the Pd/WO₃-ZrO₂ catalyst exhibitedexcellent catalytic activity for n-heptane isomerization. Compared with thePd/WO₃-ZrO₂ catalyst, the Ni/WO₃-ZrO₂ catalyst exhibited the same n-heptaneconversion, but slightly lower selectivity.For the WO₃-ZrO₂ support dried in supercritical ethanol (SCD), it was beforecalcination that the tetragonal ZrO₂ crystalline phase had formed. Compared withthe Pd/WO₃-ZrO₂ catalyst by conventional oven drying method (CD), the one bySCD had larger surface, smaller particle size, higher dispersity of WO₃ on ZrO₂and more amount of acidity. The Pd/WO₃-ZrO₂ catalyst by SCD exhibited highselectivity for the isomerization reaction of n-heptane.