SAPO-5 分子筛的制备及其催化合成对氨基苯酚

 采用水热法在常规无氟和含氟体系中制备了磷酸硅铝 (SAPO-5) 分子筛, 并运用 X 射线衍射、扫描电镜、固体核磁共振、红外光谱和氨程序升温脱附等方法对样品进行了表征, 考察了初始凝胶硅含量及 HF 的加入对分子筛结构、硅插入方式、酸性及其在硝基苯加氢合成对氨基苯酚 (PAP) 反应过程中催化苯基羟胺重排反应活性的影响. 结果表明, 含 HF 体系中合成的分子筛中 Si 的取代以 SM3 机理为主, 产生了较多的 Si(4Si) 纯硅区, 导致分子筛表面酸量降低, 酸强度增加. HF 的存在提高了 SAPO-5 分子筛晶化的完整度, 抑制了高硅含量条件下凝胶态 SiO2 的产生, 促进了 Si 在分子筛结构中的插入. 在硝基苯加氢合成 PAP 反应过程中, 含氟体系中合成的分子筛催化重排反应性能明显高于无氟体系合成的分子筛样品, PAP 最高收率达 53.2%.

Preparation of SAPO-5 and Its Catalytic Synthesis of p-Aminophenol

Silicoaluminophosphate molecular sieves (SAPO-5) were synthesized by hydrothermal crystallization using both a conventional aqueous medium and a HF medium. The SAPO-5 samples were characterized by X-ray diffraction, scanning electron microscopy, solid state NMR, Fourier transform infrared reflectance spectroscopy, and temperature-programmed desorption of adsorbed NH3. The effect of Si content and presence of HF in the initial gel on the structure of the SAPO-5 synthesized and the manner of Si incorporation into the framework were investigated. Their acidity and catalytic activity for phenylhydroxylamine (PHA) rearrangement in the synthesis of p-aminophenol (PAP) from nitrobenzene were studied. The incorporation of Si in the samples prepared in the presence of HF was mainly by the SM3 mechanism and patches of Si(4Si) were predominant. This resulted in a decrease in the acid amount and increase in acid strength. The presence of HF during synthesis increased the integrity of the SAPO-5 crystal and helped incorporate more Si in the SAPO-5 structure by inhibiting the polymerization of Si species to a reticulated silica gel. The samples prepared in the HF medium exhibited better catalytic performance for PHA rearrangement in the synthesis of PAP, and a PAP yield of 53.2% could be obtained.