Abstract:

Alumina-doped Pt/WO₃/ZrO₂ catalysts were prepared using either a constant or variable pH method. The obtained catalyst samples were characterized using N₂ adsorption, X-ray diffraction, ultraviolet-visible diffuse reflectance, CO chemisorption, X-ray photoelectron spectroscopy, ²⁷Al magic-angle spinning nuclear magnetic resonance, and infrared spectroscopy of adsorbed pyridine. Compared to the catalyst prepared using the variable pH method, the catalyst prepared using the constant pH method had a higher surface area and Pt dispersion. More Brönsted acid sites were generated in the presence of H₂ on the latter catalyst, and this was responsible for its higher catalytic activity in n-heptane hydroisomerization. When the reaction temperature was 200℃ and the weight hourly space velocity of n-heptane was 0.9 h^-1, the Pt/WO₃/Al₂O₃-ZrO₂ catalyst prepared using the constant pH method gave 70.0% conversion of n-heptane, which was significantly greater than the conversion obtained using the corresponding catalyst prepared using the variable pH method (43.5%).

Key words: Platinum, Tungsten oxide, Zirconia, Alumina doping, Preparative method, n-Heptane hydroisomerization, Protonic acid sites