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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 structures of HZSM-5 zeolites treated by hydrothermal treatment at low temperature (573-823K) were investigated by XRD, IR, XPS, temperature programmed desorption (TPD), low temperature nitrogen adsorption, TG deposition and atmospheric pressure pulse and continuous flow microreactor. And the changes of the surface properties, investigated the zeolite catalyst activity and stability changes. The results showed that the structure of HZSM-5 zeolite did not change greatly after hydrothermal treatment at low temperature. The results of XPS showed that there was a dealumination at 723K and a slight shrinkage of the unit cell volume above 773K, but no crystal symmetry was observed. TPD and IR data showed that as the hydrothermal treatment temperature increased, the total surface acid decreased, the strong acid center decreased linearly, and the hydrothermal treatment decreased the number of acid sites on the surface. The conversion reaction of n-hexane, heptene and methanol showed that the 673K- The highest catalytic activity, the selectivity of aromatic hydrocarbons and C_ (5 +) aliphatic hydrocarbons in the product all showed the maximum and the minimum value. The increase of the catalytic activity of the zeolite appeared before the dealumination of the zeolite, and the number of acid sites on the surface B and L was nearly equal , Higher than 673K treatment significantly increased the stability of the catalyst.