Influence of preparative method on Al2O3-doped Pt/WO3-ZrO2 catalyst for n-heptane isomerization

Abstract

Alumina-doped Pt/WO 3 /ZrO 2 catalysts were prepared using either a constant or variable pH method. The obtained catalyst samples were characterized using N 2 adsorption, X-ray diffraction, ultraviolet-visible diffuse reflectance, CO chemisorption, X-ray photoelectron spectroscopy, 27 Al 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 H 2 on the latter catalyst, and this was responsible for its higher catalytic activity in n -heptane hydroisomerization. When the reaction temperature was 200 °C and the weight hourly space velocity of n -heptane was 0.9 h −1 , the Pt/WO 3 /Al 2 O 3 -ZrO 2 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%). 采用恒pH法和非恒pH法制备了Al 2 O 3 掺杂的Pt/WO 3 /ZrO 2 催化剂, 并用N 2 吸附-脱附、X射线衍射、紫外-可见漫反射、CO化学吸附、X射线光电子能谱、 27 Al魔角旋转核磁共振和吡啶吸附红外等技术对催化剂进行了表征. 结果表明, 相比于非恒pH法制备的催化剂, 恒pH法制备的催化剂具有较高的比表面积和Pt分散度, 在H 2 气氛中产生更多的B酸位, 从而表现出更高的催化正庚烷临氢异构化反应活性; 在200 °C和质量空速0.9 h −1 的反应条件下, 正庚烷转化率达70.0%, 明显高于非恒pH法制备的催化剂(43.5%). An Al 2 O 3 -doped Pt/WO 3 /ZrO 2 catalyst prepared using a constant pH method exhibited significantly higher activity in n -heptane hydroisomerization than did the corresponding catalyst prepared using a variable pH method. This was because more Brnsted acid sites were generated on the former catalyst in the presence of H 2 .