SBA-15负载的Cu(Ⅱ)席夫碱配合物催化的苯乙烯氧化反应制备苯甲醛

采用一步法将原硅酸四乙酯与3-氨丙基三乙氧基硅烷在表面活性剂P123作用下,酸性共水解制备出氨基功能化的介孔分子筛SBA-15(NH2-SBA-15),再利用其中氨基与水杨醛的缩合反应制备SBA-15固载的席夫碱,该席夫碱与Cu(NO3)2溶液反应最终制成固定于SBA-15的Cu(II)席夫碱配合物多相催化剂Cu-SBA-15.采用X射线衍射、红外光谱仪、紫外可见分光光度计、场发射电镜、透射电镜、N2吸附-脱附、元素分析、原子发射光谱和热重分析对催化剂进行了表征,并将此催化剂用于无有机溶剂条件下催化氧化苯乙烯制备苯甲醛,考察了反应时间、反应温度、H2O2用量、水的用量、催化剂用量对反应的影响.当反应温度为100°C,反应时间8 h,H2O2与苯乙烯的摩尔比为2:1,不额外添加溶剂,且催化剂用量为3.8 wt%时,苯乙烯的转化率最高为84.4%,苯甲醛选择性为83.9%,催化剂的TOF值为261.1 h–1,并且重复使用3次后活性没有明显下降.规则的孔道、较大的比表面积以及分布均匀的活性中心可能是催化剂活性提高的原因.

Catalytic oxidation of styrene to benzaldehyde over a copper Schiff-base/SBA-15 catalyst

The amino-modified mesoporous material SBA-15 (NH₂-SBA-15) was prepared via co-condensation of tetraethylorthosilicate with 3-aminopropyltriethoxysilane in the presence of an amphiphilic triblock copolymer as a pore-directing agent under acidic conditions. The SBA-15-supported Cu Schiff-base complex (Cu-SBA-15) was then synthesized by condensation of salicylaldehyde with NH₂-SBA-15, followed by the addition of a solution of Cu(NO₃)₂. The supported complex was systematically characterized by elemental analysis, inductive coupled high frequency plasma atomic emission spectrometry, powder X-ray diffraction, Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, field scanning electron microscopy, transmission electron microscopy, N₂ absorption-desorption, and thermo gravimetric analysis, and was used as the catalyst for the selective oxidation of styrene to benzaldehyde. The influence of the reaction parameters was assessed. The maximum conversion of styrene was 84.4% and the selectivity for benzaldehyde was 83.9%, when the reaction was conducted with a 2:1 molar ratio of H₂O₂:styrene in the presence of 3.8 wt% catalyst at 100 ℃ for 8 h. The TOF was 261.1 h^-1, and the catalyst could be used three times without significant loss of activity. The uniformly sized pore channels, high specific surface area, and well-distributed active centers of the catalyst may contribute to the high activity.