具有多级孔道结构、高水热稳定性的含氧化镁Silicalite-1分子筛的合成

通过焙烧将分散在多孔氧化硅母体中的硝酸镁转化成高分散的MgO物种, 然后使用四丙基氢氧化铵(TPAOH)作为结构导向剂, 将含MgO 的母体通过水热晶化合成MgO/silicalite-1 分子筛复合物. X 射线衍射(XRD)、能量X射线光谱(EDX)和透射电镜(TEM)的结果表明MgO物种被均匀地分散在silicalite-1 分子筛晶体中. 将酸处理脱除氧化镁前后的样品在100%水蒸汽800℃ 条件下老化, 结果表明MgO 的引入有效地提高了分子筛的水热稳定性. 此外, 酸洗脱除MgO/silicalite-1分子筛中的MgO提高了分子筛结晶度, 同时引入了一定的介孔. N₂物理吸附-脱附数据证明了酸洗后分子筛中介孔的存在. 水热稳定性的提高和介孔的引入对于在高温下保持催化剂的孔道结构, 提高催化剂的抗积碳能力, 降低催化剂的失活速率以及延长催化剂的使用寿命起着非常重要的作用.

Synthesis of Hierarchical MgO-Containing Silicalite-1 Zeolites with High Hydrothermal Stability

Hierarchical MgO/silicalite-1 composites were synthesized via hydrothermal treatment of MgO-supported porous silica using tetrapropylammonium hydroxide (TPAOH) as a template. MgO species were introduced into porous silica via solid-state grinding and subsequent calcination. X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM) results indicated that MgO was uniformly distributed in the zeolite crystals. The hydrothermal stability of MgO/ silicalite-1 before and after acid washing was detected by treatment at 800℃ in 100% steam for 10 h. The introduction of MgO increased the hydrothermal stability of MgO/silicalite-1 samples. Furthermore, acid washing could remove MgO impurities, increasing the relative crystallinity of samples compared with that of calcined MgO/silicalite-1 and introducing mesopore into zeolite simultaneously. N₂ adsorption-desorption measurements indicated that mesopores were generated in the zeolite crystals by the removal of MgO species. The improved hydrothermal stability and the generation of mesopores in these MgO/silicalite-1 samples play important roles in preserving zeolite structure, enhancing coke tolerance, slowing deactivation, and extending catalyst life during high-temperature reaction.