热处理对HZSM-5结构、酸性及催化乙醇脱水反应性能的影响

对商用HZSM-5分子筛进行高温热处理,利用X射线衍射(XRD)、核磁共振波谱法(²⁷Al-MAS NMR)低温氮吸附、电感耦和等离子体放射光谱(ICP-AES)、氨-程序升温脱附(NH₃-TPD)和吡啶吸附傅里叶变换红外(FT-IR)光谱等技术对高温热处理改性前后样品进行了表征,并考察了高温热处理对分子筛的结构、酸性及催化乙醇脱水制乙烯反应性能的影响。结果表明,热处理改性后的HZSM-5分子筛发生骨架脱铝,B酸减少,L酸增多,孔容增大,出现新的介孔;适中的酸性位和复合型的介-微双孔道结构使其减少了反应中的副反应,乙烯的选择性得到提高,催化剂寿命显著提高。

Effect of heat treatment on the structure, acidity and catalytic performance of HZSM-5 zeolites in ethanol dehydration

Heat treatment at high temperature was used to modify HZSM-5 zeolites.The HZSM-5 samples before and after heat treatments were characterized by X-ray diffraction(XRD),27Al-MAS NMR,N2 adsorption,inductively couple plasma emission spectroscopy(ICP-AES),temperature-programmed desorption of ammonia(NH3-TPD),and Fourier transform infrared(FT-IR) spectroscopy of adsorbed pyridine.The effects of heat treatment conditions on the structure,acidity,and catalytic performance of HZSM-5 zeolites in dehydration of ethanol to ethylene were investigated.The results showed that the heat treatment leads to dealuminization from the zeolite framework and channels,which may decrease the amount of Bronsted acid sites,increase the Lewis acid sites and the pore volume,and form new mesopores.When the heat-treated HZSM-5 is used as the catalyst in ethanol dehydration,owing to its appropriate acidity and binary meso/micro porous structure,the side reaction is reduced and the selectivity to ethylene and the catalyst life time are increased significantly.