同晶外延生长法合成MFI型核壳复合分子筛  

Synthesis of core-shell structured MFI-type composite zeolites by isomorphous epitaxial growth

作　　者：崔丽萍[1] 王成雄[2] 赵云昆[2] 李忠[1] 杨冬花[1] 

机构地区：[1]太原理工大学煤科学与技术教育部和山西省重点实验室,山西太原030024 [2]昆明贵金属研究所稀贵金属综合利用新技术国家重点实验室,云南昆明650106

出　　处：《燃料化学学报》2016年第9期1145-1152,共8页Journal of Fuel Chemistry and Technology

基　　金：山西省科技基础条件平台建设项目(2015091009)资助~~

摘　　要：采用二次热液结晶法,以四丙基氢氧化铵水溶液预处理过的低硅ZSM-5分子筛为晶核,通过调控p H值、水量和晶化时间等二次结晶条件,在晶核上外延生长了高硅ZSM-5壳,制备了MFI/MFI核壳型复合分子筛。通过X射线衍射、扫描电镜、能量色散谱仪、透射电子显微镜、N2吸附-脱附和NH3-程序升温脱附等手段表征了所合成的核壳分子筛的晶体结构、表面形态及核/壳界面,并对它们的结构参数以及酸性进行了初步评估。结果表明,核壳复合分子筛的壳层由多层200 nm的MFI沸石晶粒组成;高硅ZSM-5分子筛壳层的生成,引入了介孔结构,显著增大了外比表面积;同时,核壳结构的形成降低了复合分子筛酸性和外表面的酸密度,但增加了弱酸量。当二次晶化母液p H值为8.5,H2O/SO2物质的量比为30,晶化时间为24 h时,高硅分子筛壳层更易可控生长。MFI/MFI core-shell composite zeolites with a low-silica ZSM-5 core and a high-silica shell were successfully synthesized by secondary hydrothermal crystallization on the low-silica ZSM-5 cores that was pretreated with a basic TPAOH aqueous solution; the preparation parameters for shell growth including the pH value, water amount, and crystallization time were well considered. The crystal structure, surface morphology, core/shell interface, textural properties and surface acidity of the resultant core-shell zeolites were characterized by X-ray diffraction, scanning electron microscopy, energy dispersive spectrometer, transmission electron microscopy, N2 physisorption and NH3 temperature programmed desorption. The results indicated that in the core-shell composite zeolites, high-silica ZSM-5 shell with a particle size of 200 nm is well developed on the surface of core crystal. The growth of ZSM-5 shell results in an increase of external surface area, decrease of external acid density and increase of weak acid sites without influencing pore structure. The isomorphous epitaxial growth of high-silica ZSM-5 shells can be effectively controlled under the conditions of a pH value of 8. 5, H2 O/SiO2 mol ratio of 30 and crystallization for 24 h during the secondary crystallization.

关 键 词：ZSM-5 二次结晶 核/壳结构 复合分子筛 表面酸性 

分 类 号：TQ426[化学工程]