摘要
采用十六烷基三甲基溴化铵(CTAB)和六亚甲基亚胺(HMI)组成双模板体系,以气相二氧化硅为硅源,在150 ℃下动态原位合成了薄层的MWW型MCM-22分子筛纳米片,并考察了 CTAB添加量对分子筛产物的影响.采用粉末X射线衍射(PXRD)、扫描电子显微镜(SEM)、N2吸附-脱附、氨气程序升温脱附(NH3-TPD)、高倍透射电子显微镜(HRTEM)、吡啶红外(Py-IR)和2,6-二叔丁基吡啶红外(DTBPy-IR)测试方法对合成的分子筛样品进行表征.结果表明:采用双模板体系可以制备出5～10nm的薄层MWW型纳米片.同时,通过偏三甲苯异构化反应对样品的催化性能进行了表征,催化结果显示样品d-MWW-4％CTAB具有较好的催化性能,其中偏三甲苯的质量转化率、均三甲苯质量收率及均三甲苯选择性分别为34.97％、22.42％和64.09％,这主要归因于薄层纳米片MCM-22具有的较大外表面积和片层间形成的晶间介孔结构.
Abstract
A nano-thin layer MWW-type zeolite,derived from fumed silica,was dynamically in-situ synthesized at 150 ℃ using a dual-template system of cetyltrimethylammonium bromide(CTAB)and hexamethylene imine(HMI).The effect of CTAB amount on the zeolite was also investigated.The nano-thin layer samples were characterized using powder X-ray diffraction(PXRD),scanning electron microscopy(SEM),N2 adsorption-desorption,ammonia temperature programmed desorption(NH3-TPD),high-resolution transmission electron microscopy(HRTEM),pyri-dine infrared spectroscopy(Py-IR),and 2,6-di-tert-butylpyridine infrared spectroscopy(DTBPy-IR).The results indicated that MWW nanosheets with a thickness of 5-10 nm can be prepared using the double template system.Furthermore,the catalytic performance of the samples was evaluated through the isomerization of the trimethylben-zenes reaction.The catalytic results show that the sample d-MWW-4％CTAB exhibits good catalytic performance,with the conversion of 1,2,4-trimethylbenzene,the yield of 1,3,5-trimethylbenzene,and the selectivity of 1,3,5-trimethylbenzene being 34.97％,22.42％,and 64.09％,respectively.This is primarily attributed to the external sur-face area and interlayer mesoporous structure formed in the nano-thin layer MCM-22.
维普
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