摘要
用XRD,IR,XPS,程序升温脱附(TPD)、低温氮吸附、TG积炭反应和常压脉冲与连续流动微反色谱装置研究了低温(573～823K)水热处理 HZSM-5沸石的结构和表面性质的变化,考察了沸石催化剂活性和稳定性的变化规律。结果表明,经低温水热处理后,HZSM-5沸石的结构没有大的改变,XPS结果表明在723K出现脱铝作用,在773K以上晶胞体积略有收缩,但未出现晶体对称性变化,NH_3-TPD和IR数据表明随水热处理温度提高,表面总酸减少,强酸中心呈线性下降,水热处理使表面B酸中心数大幅度减少,正己烷、庚烯和甲醇的转化反应表明673K处理的沸石具有最高催化活性,产物中芳烃和C_(5+)脂肪烃选择性均呈现最大值和最小值,沸石催化活性增大现象出现在沸石脱铝作用之前,此时表面B,L酸中心数接近相等,高于673K处理使催化剂稳定性显著增加。
The structure and catalytic behavior of HZSM-5 zeolite catalyst pretreated with flowing steam (partial pressure 80.0 KPa) for 4h at 573 -823K were studied. The results revealed that the crystalline structure and the orthorhombic symmetry showed no discernible change, but the cell volume of the zeolite steam treated at above 773K contracted slightly. XPS analysis also confirmed that the dealumination of the zeolite occurred at steaming temperature above 723K. NH3-TPD and IR data indicated that when the steaming temperature increased from 573 to 823K, the strong acid sites of HZSM-5 decreased linearly,and the B acid sites decreased sharply with a gradual increase in the relative ratio of L acid sites. The conversion of n-hexane, heptene-1 and methanol over the zeolite sample steam-treated at 673K showed an activity maximum, in spite of a great reduction of strong acid sites, and selectivity for aromatics and C5+ aliphatics appeared a maximum and a minimum respectively. The enhancement in catalytic activity of the steam-treated HZSM-5 zeolite could be observed only before dealumination. The stability of HZSM-5 catalyst steam-treated at temperature above 673K increased remarkably.
基金
国家自然科学基金
山西省自然科学基金
