低温晶化温度对B-ZSM-5及Ti-ZSM-5物理化学性质的影响

采用变温晶化方法, 通过改变低温段晶化温度, 水热合成B-ZSM-5沸石. 以B-ZSM-5沸石为母体, 经脱硼处理后, 与TiCl4进行气固相取代反应制得Ti-ZSM-5样品. 采用扫描电子显微镜(SEM)、X射线衍射(XRD)、傅里叶变换红外(FT-IR)光谱、紫外-可见(UV-Vis)光谱、电感耦合等离子体原子发射光谱(ICP-AES)、拉曼光谱、N2吸附-脱附及1,2,4-三甲苯物理吸附等手段对其进行了表征, 并考察了Ti-ZSM-5样品在苯酚羟基化反应中的性能. 结果表明, 合成的母体均为长方体颗粒的聚集体且具有完整的MFI拓扑结构, 但其聚集体颗粒大小、载钛量、孔容及比表面积却存在明显差异; 低温晶化最佳温度为333-353 K, 以此条件下合成出以B-ZSM-5为母体制得的Ti-ZSM-5具有更小的颗粒尺寸、较大的孔容及比表面积, 在苯酚羟基化反应中表现出更加优异的催化性能. 在苯酚与过氧化氢的摩尔比为3的条件下, 苯酚转化率最高可达到20.5%.

Effect of Crystallization Temperature on Physico-Chemical Properties of B-ZSM-5 and Ti-ZSM-5

B-ZSM-5 zeolites with different crystal sizes were synthesized by adjusting hydrothermal synthesis temperature. Ti-ZSM-5 samples were prepared by gas-solid reaction using acid-treated B-ZSM-5 as precursors with gaseous TiCl_4. The samples were characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), Fourier-transform infrared (FT-IR) spectra, ultraviolet-visible (UV-Vis) spectroscopy, inductively coupled plasma atomic emission spectrometry (ICP-AES), Raman spectra, nitrogen adsorption-desorption, and 1,2,4-trimethylbenzene adsorption. The catalytic performance of Ti-ZSM-5 for phenol hydroxylation was investigated. Results showed that all the precursors were agglomerated by the small cuboids particles and had MFI topology structure, but there were some differences in the crystal size, the amount of framework titanium species, and pore volume. The optimized temperature range of the low-temperature crystallization stage is from 333 to 353 K for the synthesis of B-ZSM-5. Moreover, Ti-ZSM-5 sample using this B-ZSM-5 as the precursor has a better catalytic performance for phenol hydroxylation, because of the smaller cuboids particles, the larger pore volume and surface area. In phenol hydroxylation, when the molar ratio of phenol to hydrogen peroxide was 3, the conversion of phenol was 20.5%.