高纯度中孔分子筛MCM-41的合成与表征

用不同pH值的混合物制备了不同孔径的全硅MCM-41和不同金属离子取代的M-MCM-41(M=Al,Mn,Fe和V)分子筛.这些试样均呈现MCM-41的X射线粉末衍射特征峰和Ⅳ型氮气吸附等温线,但混有不同含量的无定形氧化硅.样品中MCM-41晶体的含量与溶胶的pH值和所用表面活性剂的碳链链长有关.骨架硅的金属离子取代降低了MCM-41的有序度,并且(100)面衍射峰强度从Al到V依次减弱.

Synthesis and Characterization of High-quality Mesoporous Molecular Sieve MCM-41s

Siliceous MCM-41 samples with two different pore size and metal substituted MCM-41 samples with different metals have been synthesized at different pH of the mixture, and characterized by X-ray powder diffraction and nitrogen adsorption analysis. The results show that all the samples exhibit a typical XRD diffraction of MCM-41 and an adsorption isotherm of type Ⅳ, but there exists a considerable amount of amorphous siliCA In the samples. The sample prepared at pH=11(MCM-3) shows the best in quality among the others, and has less content of amorphous silica phase. When the MCM-3 is regarded as a standard, the sample prepared without pH adjustment contains only 36% of pure MCM-41 crystallites, while the sample prepared at pH=10.5 has 84% of pure MCM-41 phase. It has also been observed that the quality of the resulted samples is decreased when a shorter chain surfactant is used. When the metal substituted M-MCM-41 (M=Al, Mn, Fe, V) is prepared at pH=11, their quality can be improved. However, the diffraction intensity of d₁₀₀phase is still lower than that of the corresponding siliceous MCM-41, and decreases accordingly from Al to V.