贵金属负载型核壳结构催化剂的制备及其催化性能

以十六烷基三甲基溴化铵(CTAB)为表面活性剂,尿素为碱源,正硅酸四乙酯(TEOS)为硅源,在环己烷和正戊醇组成的微乳体系中制备了以微孔ZSM-5分子筛为核,树枝状介孔SiO_2为壳的多级孔核壳结构分子筛。考察制备温度、时间、尿素添加量以及TEOS添加量等制备条件对制备催化剂所需载体的影响,并采用X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)和N2吸附-脱附等手段对分子筛样品进行了表征。结果表明,制备温度为100~120℃,时间为4 h,尿素与TEOS物质的量之比为1和TEOS与ZSM-5物质的量之比为0.9~1.2时,得到的核壳结构分子筛呈现出优良的单分散性、完整性以及水热稳定性。最终在树枝状介孔SiO_2壳层负载高分散贵金属Pt,得到的双功能催化剂Pt/ZSM-5@MS在催化丙酮一锅法制备甲基异丁基酮(MIBK)反应中表现出较高的活性及良好的循环使用性能。

Preparation and Catalytic Performance of Noble Metal Loaded Core-Shell Structured Catalyst

Core-shell structured zeolites with ZSM-5 as core and dendritic SiO2 as shell were successfully prepared using cetyltrimetylammonium bromide (CTAB) as surfactant, urea as alkaline source and tetraethyl orthosilicate (TEOS) as silicate source in the microemulsion system composed of cyclohexane and n-pentanol. The effects of the preparation conditions such as temperature, time, addition of urea and TEOS on the preparation of the catalyst were investigated. The zeolites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and N2 adsorption-desorption. The results indicated that the obtained core-shell structured zeolites exhibited excellent monodispersity, integrity and hydrothermal stability when the preparation temperature was between 100-120℃ , reaction time was 4 h, the molar ratio of urea to TEOS was 1 and the molar ratio of TEOS to ZSM-5 was 0.9-1.2. Finally, the noble metal Pt was loaded on the dendritic mesoporous SiO2 shell and the obtained bifunctional catalysts of Pt/ZSM-5@MS exhibited high catalytic activity and reusability in the one-pot preparation of methyl isobutyl ketone (MIBK) from acetone.