金属离子改性对纳米SO_4^(2-)/ZrO_2固体超强酸性能的影响

Effects of Doping Metal Ions on Performance of SO_4^(2-)/ZrO_2 Nanosuperacids

制备了一系列金属离子改性的SO42-/ZrO2固体超强酸(SZ)。用N2吸附比表面积测定、X射线衍射、透射电子显微镜、扫描电子显微镜、差热分析等方法对固体超强酸进行表征。以正己烷的裂解为探针反应,考察了固体超强酸催化剂的催化活性和乙烯选择性。实验结果表明,不同金属离子改性的SZ均为纳米粒子(粒径小于40nm),但其催化剂的催化活性不同。金属离子和SO42-的共同作用使得ZrO2由四方晶形向单斜晶形转化的温度升高,晶粒粒度减小,比表面积增大,催化活性提高。催化剂催化正己烷裂解的活性由高到低的顺序为:N i/SZ>A l/SZ>Sn/SZ>SZ>Ag/SZ。

A series of sulfated zirconia—SO4^2-/ZrO2 （SZ）modified by doping metal ions, such as Ni^2＋ , Al^3＋ ,Sn^4＋ , were prepared by impregnation of zirconium hydroxide in H2SO4 and different metal ion solutions. The solid nanosuperacids were characterized by BET, XRD, TEM, SEM, DTA and chemical method. Activities and ethylene selectivities of catalysts were evaluated using cracking of n- hexane as probe reaction. SO4^2-/ZrO2 modified by doping different metal ions behaved differently and all catalysts particles were in nano - size （ ＜ 40nm）. Joint effects of metal ions and SO4^2- increased crystal transition temperature of ZrO2 from tetragonal to monoclinic. At the same time, crystallite size was decreased and specific surface area increased significantly.Activity of SO4^2-/ZrO2 catalysts modified by various metal ions in n- hexane cracking was in order of Ni/SZ ＞Al/SZ ＞ Sn/SZ＞ SZ ＞ Ag/SZ.