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在不同温度下焙烧处理 HZSM—5沸石;用粉末 X 射线衍射、扫描电镜、固体~(27)AL—NMR 研究了样品的结构变化;所得 NH_3—TPD,IR 谱表征了样品的表面酸性;在甲苯歧化反应中考察了其催化性能。结果发现:ZSM—5沸石经高温焙烧后发生了结构脱 Al,生成了无定型、酸性极弱的氧化铝,致使样品的结晶度下降,酸性降低,B 酸向 L 酸转化;由焙烧 ZSM—5催化的甲苯歧化反应,甲苯的转化率下降,对二甲苯的选择性升高。由此得出:甲苯歧化的活性由催化剂的表面酸量决定。对二甲苯选择性主要由酸类型控制。
HZSM-5 zeolite was calcined at different temperatures. The structural changes of the samples were investigated by X-ray powder diffraction, scanning electron microscopy and solid-27 atomic-nuclear magnetic resonance spectroscopy. The surface acidity of samples was characterized by NH_3-TPD and IR spectra. Toluene disproportionation reaction was investigated for its catalytic properties. The results showed that zeolite ZSM-5 was calcined at high temperature, and the structure of AlZSM-5 zeolite was decomposed. The amorphous, extremely weakly acidic alumina was formed, which led to the decrease of the crystallinity, the decrease of acidity and the conversion of B acid to L acid. 5 catalyzed toluene disproportionation reaction, the conversion of toluene decreased, the selectivity of paraxylene increased. It follows that the activity of toluene disproportionation is determined by the surface acidity of the catalyst. Paraxylene selectivity is dominated by the acid type.