ZSM-5/MCM-41复合分子筛的制备及对乙醇脱水的催化活性

以微孔ZSM-5分子筛为母体,采用NaOH溶液对其进行预处理,再在水热条件下以十六烷基三甲基溴化铵（CTMAB）为模板剂制备了ZSM-5/MCM-41介微孔复合分子筛,考察了预处理温度、晶化温度等因素对复合分子筛结构和形貌的影响。进一步考察了该复合分子筛催化剂在乙醇脱水反应中的催化活性。结果表明,ZSM-5分子筛在2.0 mol/L NaOH溶液中于110℃预处理20 h,再于110℃水热晶化20 h制备的分子筛具有良好的介微孔复合结构;该复合分子筛经NH4NO3溶液离子交换制备的氢型催化剂在乙醇脱水催化反应中表现出良好的性能。当乙醇WHSV=0.5 h-1时,最佳反应温度为240～255℃,乙醇转化率〉99%,乙烯选择性〉96%。

Preparation of micro/mesoporous ZSM-5/MCM-41 composite molecular sieve and its catalytic performance on the dehydration of ethanol

Micro/mesoporous ZSM-5/MCM-41 composite molecular sieves were prepared with commercial ZSM-5 zeolite as silica-alumina sources by the treatment of aqueous NaOH solution and with further hydrothermal crystallization using cetyltrimethylammonium bromide(CTMAB)as a structure-directing agent.The influence of various parameters,especially the temperature of the treatment and/or that of the crystallization processes on the crystallization and the morphology of the micro/mesoporous composites has been investigated.The obtained composite materials were further prepared to become catalysts and their catalytic performance on the dehydration of ethanol was carefully illustrated.The results show that micro/mesoporous ZSM-5/MCM-41 composite can be successfully obtained by a two-step method and the optimal condition is that ZSM-5 zeolite was firstly treated at 110 ℃ in a 2.0 mol/L aqueous NaOH solution for 20 h and further crystallized under 110℃ for 20h.H-type catalysts were prepared by ion exchange of the prepared micro/mesoporous ZSM-5/MCM-41 composite with NH4NO3 solution.They show wonderful catalytic performance on the dehydration of ethanol.The conversion of ethanol and the selectivity of ethylene is up to 99% and 96% respectively when the reaction temperature ranges from 240 to 255 ℃ under 0.5 h-1 weight hourly space velocity(WHSV)of ethanol.