碱处理对X沸石孔结构影响的研究

Effects of Alkali-Treatment on the Pore Structure of Zeolite X

研究了X型沸石经碱溶液处理后介孔的形成,考察了碱溶液浓度、碱处理温度和时间对形成介孔的影响。并采用ICP、N2吸附-脱附、SEM、XRD等进行表征。结果表明:碱处理抽提沸石骨架上的硅使处理后样品硅铝比发生变化,从而改变了X型沸石的性能;浓度为0.05mol·L-1的NaOH溶液70℃下处理30min是形成介孔的最佳条件,在此条件下形成介孔孔容为0.24cm3·g-1,孔径分布为2.3～8nm的介孔,比表面积从处理前的352.69m2·g-1升高到443.11m2·g-1。而碱处理温度低于70℃,沸石骨架上硅不易抽提;碱溶液浓度高于0.05mol·L-1或碱处理时间长于30min,X型沸石则易形成大孔。样品经亚甲基蓝吸附测试,证实X型沸石碱处理后确实形成了一定量的介孔。

The formation of mesoporous structure of zeolite X treated with alkali solution was studied, The effects of the concentration of alkali solution used, treating temperature and time on the formation of mesoporous structure were investigated. The zeolites after alkali treatment were characterized by ICP, N2 adsorption-desorption, SEM, and XRD, The results reveal that alkali-treatment can change the Si/Al molar ratio of zeolite X, and thus modify its properties, It was found that the Si in the framework of zeolite X is difficult to be removed when the alkali-treatment temperature is lower than 70℃, and zeolite X is prone to form macropores when used concentration of NaOH solution is higher than 0,05 mol·L^-1 and/or the alkali-treatment time is longer than 30 min. When the zeolite X was treated under the optimal conditions （using 0.05 mol·L^-1 NaOH solution at 70℃ for 30 min）, the mesoporous zeolite with mesoporous volume of 0.24 cm^3·g^-1, pore size distributions of 2.3-8 nm and specific surface area of 443.11 m^2·g^-1can be obtained. The methylene blue adsorption tests show that the adsorption equilibrium amount of methylene blue adsorbed by alkali-treated zeolite X is larger than that by the untreated zeolite X, which confirms that a certain amount of mesopores are indeed formed in the zeolite X after alkali-treatment.