CeX分子筛催化分子氧选择性氧化环己烷

SELECTIVE AEROBIC OXIDATION OF CYCLOHEXANE BY CeX ZEOLITE

用液相离子交换法引入Ce离子对NaX分子筛改性,对比Ce(Ⅲ)X、Ce(Ⅳ)X对环己烷氧化反应的催化效果,主要考察了Ce(Ⅲ)X的不同离子交换度,以及不同焙烧气氛下离子占位和价态变化对环己烷氧化的影响。结合X射线衍射、电感耦合等离子体原子发射光谱仪、氮气吸附-脱附、X射线光电子能谱仪等方法对改性催化剂进行分析。研究表明,Ce(Ⅲ)X催化环己烷氧化反应的转化率是NaX分子筛的2.6倍,略高于Ce(Ⅳ)X分子筛;随着Ce(Ⅲ)X的离子交换度由13.4%增加到76.2%,环己烷的转化率由3.15%提高到8.54%;Ce(Ⅲ)X在真空氛围和空气氛围下焙烧,环己烷转化率分别降至7.5%和5.7%,催化活性的降低与Ce(Ⅲ)离子向方钠石笼迁移和价态变化有关。同时得出最优的工艺条件:氧气压力为1.5 MPa,反应温度为150℃,搅拌速率为800 r min,反应时间为2 h。在最优条件下环己烷转化率为8.54%,目标产物(环己酮和环己醇)选择性为86.39%。

In this paper,NaX zeolite was modified with Ce ions by liquid phase ion exchange method.After comparing the catalytic effects of Ce(Ⅲ)X and Ce(Ⅳ)X,the effect of ion occupation and valence state on cyclohexane oxidation were investigated under different ion exchange rates and different calcination atmosphere.The modified catalysts were characterized by ICP,XRD,BET,XPS,H 2-TPR.The results showed that the conversion of cyclohexane on Ce(Ⅲ)X was 2.6 times higher than that on NaX,and slightly higher than that on Ce(Ⅳ)X;the conversion of cyclohexane was increased from 3.15%to 8.54%with the Ce(Ⅲ)X ion occupation increasing from 13.4%to 76.2%,and the conversion of cyclohexane was reduced to 7.5%and 5.7%with Ce(Ⅲ)X calinated in vacuum and air,respectively.The reduction of catalytic activity was related to the migration of Ce(Ⅲ)ions to sodalite cages and valence variation.At the same time,the optimum process conditions were obtained:oxygen pressure was 1.5 MPa,reaction temperature was 150℃,stirring speed was 800 r min,and reaction time was 2 hours.The conversion of cyclohexane was 8.54%,and the selectivity of target products(cyclohexanone and cyclohexanol)was 86.39%under the optimum process conditions.