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用离子交换法测定了不同温度下焙烧的HZSM-5沸石表面的B酸量;对用离子交换、TPD及IR等方法测定的酸性结果进行了关联;讨论了表面酸性质对乙酸和乙醇的酯化及乙醇分子间缩合反应活性的影响。结果表明,当焙烧温度低于550℃时,HZSM-5表面的B酸量(0.745—0.727mmol/g)基本上与根据骨架铝计算的理论值(0.735mmol/g)相吻合,说明交换下来的酸与沸石骨架铝密切相关。这部分B酸与HZSM-5的TPD谱图中峰Ⅱ相对应,说明它们是沸石表面的强酸中心,L酸与其它与骨架铝无直接联系的酸是较弱的酸中心。HZSM-5的催化活性随表面B酸量的下降而有规律的下降,而经Na~+充分交换后,用TPD测定的酸量与其催化活性基本无关的事实,说明酯化和乙醇缩合反应主要是在B酸中心上进行的。
The amount of B acid on the surface of HZSM-5 zeolite calcined at different temperatures was determined by ion exchange method. The acidity was determined by the methods of ion exchange, TPD and IR. The effects of surface acidity on the acidity of acetic acid and ethanol And the effect of condensation reaction between ethanol molecules. The results show that the amount of B acid on the surface of HZSM-5 (0.745-0.727 mmol / g) is basically consistent with the calculated theoretical value (0.735 mmol / g) based on framework aluminum when the calcination temperature is lower than 550 ℃, The acid is closely related to the zeolite framework aluminum. This part of B acid corresponds to the peak II in the TPD spectrum of HZSM-5, indicating that they are the strong acid sites on the surface of the zeolite. The L acid is the weaker acid center than other acids that are not directly linked to the framework aluminum. The catalytic activity of HZSM-5 decreases regularly with the decrease of acid content on the surface. However, the fact that the amount of acid measured by TPD is almost irrelevant to its catalytic activity after Na ~ + is fully exchanged indicates that the esterification and ethanol condensation reactions are mainly Is carried out on the B acid center.