Ag/SBA-15低温气相选择性催化氧化苯甲醇合成苯甲醛（英文）

Catalytic activity of Ag/SBA‐15 for low‐temperature gas‐phase selective oxidation of benzyl alcohol to benzaldehyde

以SBA-15为载体,采用浸渍法制备了不同Ag含量的Ag/SBA-15,通过N2吸附-脱附、X射线衍射、扫描电子显微镜、高分辨透射电子显微镜、X射线光电子能谱和电感耦合等离子体质谱对催化剂进行了表征.将Ag/SBA-15用于苯甲醇气相选择性催化氧化合成苯甲醛,研究了反应条件对转化率和选择性的影响.结果表明,Ag/SBA-15具有均一的一维孔道结构、较厚的孔壁(3–5 nm)及较大的比表面积(411–541 m2/g),其规整纳米空间的限域作用使一定负载量的Ag以纳米尺寸均匀分散于介孔SBA-15孔道内,增加了活性组分的比表面积.亲核性氧物种从Ag到SBA-15表面的氧溢流,提高了低温下Ag/SBA-15对苯甲醇气相选择性氧化合成苯甲醛的催化性能.5.3%Ag/SBA-15中的Ag粒径为5–6 nm,且均匀分散于载体孔道中,反应温度为220°C时,苯甲醇转化率为87%,苯甲醛选择性为95%;240°C时,苯甲醇转化率和苯甲醛选择性分别高达94%和97%;并在240–300°C范围内,其催化活性和选择性保持不变,表现出了良好的温度耐受能力.催化剂经活化再生可以连续使用40 h,选择性基本保持不变.

Ag/SBA-15 catalysts with different Ag contents were prepared by an impregnation method and were used for the gas-phase selective oxidation of benzyl alcohol to benzaldehyde with O2 as the oxidant.These catalysts were characterized using N2 adsorption-desorption,X-ray diffraction,scanning electron microscopy,high-resolution transmission electron microscopy,inductively coupled plasma mass spectrometry,and X-ray photoelectron spectroscopy.The effects of Ag loading,reaction temperature,and weight hourly space velocity of benzyl alcohol on the catalytic performance were investigated.The results showed that Ag was successfully incorporated into the mesoporous channels of SBA-15 and well dispersed on the surface as a result of the nano-confinement effect of SBA-15,which increased the specific surface area of the active components.Moreover,Ag/SBA-15 had a uniform pore size,a wall of thickness of 3-5 nm,and a high specific surface area of 411-541 m2/g.The catalytic activity of Ag/SBA-15 for the gas-phase selective oxidation of benzyl alcohol to benzaldehyde was enhanced by oxygen spillover of nucleophilic oxygen species from the Ag nanoparticles to the SBA-15 surface.The 5.3%Ag/SBA-15 exhibited excellent low-temperature catalytic properties; when the reaction temperature was 220 ℃,the conversion of benzyl alcohol and the selectivity for benzaldehyde reached 87% and 95%,respectively.At 240 ℃,the catalyst displayed the best catalytic properties,achieving a benzyl alcohol conversion of 94% and benzaldehyde selectivity of 97%,which remained almost constant at 240-300 ℃.This showed that Ag/SBA-15 had excellent thermal gradient stability.The catalyst could be used for 40 h and retained high catalytic activity for oxidation after treatment at 500 ℃.