硫酸根促进的纯硅MCM-41催化假性紫罗兰酮环化合成紫罗兰酮的性能

 分别采用硫酸和硫酸铵溶液作为促进剂,对MCM-41进行表面硫酸根促进,并在不同温度下焙烧制得一系列硫酸根促进的纯硅MCM-41样品SM和ASM. 采用氮吸附-脱附、吸附氨的程序升温脱附(NH3-TPD)、 热重分析(TG-DTG)、 元素分析和红外光谱(FT-IR)等表征方法对两类样品的介孔结构、硫酸根促进过程和表面酸性进行了考察,并通过环化合成紫罗兰酮这一典型的液体酸催化反应评价其催化活性. 结果表明,经450 ℃焙烧的样品(SM-450和ASM-450)中促进剂完全分解,不存在作为原始促进剂或分解中间产物的游离硫酸分子,硫酸根以双齿螯合配位结构存在于SiO2表面. 原位吡啶吸附红外光谱显示ASM-450表面同时存在L酸和B酸中心, NH3-TPD测试结果表明其酸强度较弱. SM-450和ASM-450具有与商品化氢型酸性树脂Amberlyst-15相当的催化性能,其催化作用来源于一般被认为不具备酸活性的SO2-4/SiO2表面螯合结构. 在较低反应温度下, ASM-450具有优于Amberlyst-15的催化性能,并在循环使用5次后仍保持较高的催化活性.

Catalytic Performance of Sulfated Silica MCM-41 for the Cyclization of Pseudoionone to Ionones

A series of sulfated silica MCM-41 samples denoted as SM and ASM were prepared by calcination at different temperatures using H₂SO₄ and (NH₄)₂SO₄ solution as the promoter, respectively. The mesostructure, sulfation process, and surface acidity of the two samples were investigated by N₂ adsorption-desorption, temperature-programmed desorption of adsorbed NH₃ (NH₃-TPD), thermogravimetric analysis (TG-DTG), elemental analysis, and Fourier transform infrared (FT-IR) spectroscopy. The activity of the samples for the traditional liquid acid-catalyzed cyclization reaction of pseudoionone to ionones was investigated. For the SM and ASM samples calcined at 450°C (denoted as SM-450 and ASM-450, respectively), SO₄^2- was successfully chelated onto the silica surface in bidentate complex forms, and no free H₂SO₄ molecules existed as the original promoter or intermediate of thermal decomposition inside the mesopores. The in situ pyridine adsorption FT-IR and NH3-TPD measurements revealed that ASM-450 contained both Brønsted and Lewis acid sites of weak strength. The catalytic performance of SM-450 and ASM-450 was comparable with that of the commercial acid resin Amberlyst-15, and the chelating structure of SO₄^2-/SiO₂, which was generally considered to be inactive, was responsible for the high activity. ASM-450 showed better catalytic performance compared with Amberlyst-15 at relatively low temperature, and it could be reused 5 times with good activity.