具有多级孔结构的NH4-β沸石的直接合成及其性能

以非离子表面活性剂壬基酚聚氧乙烯醚(TX-15)为模板, 设计氟化铵作为矿化剂, 在近中性条件下直接合成了具有微孔-介孔复合孔道的铵型β沸石. 合成样品采用粉末X射线衍射(PXRD), 高分辨扫描电子显微镜(SEM), 微分热重(DTG)以及氨程序升温脱附(NH3-TPD)等手段进行了表征. 结果表明, 氟离子及非离子表面活性剂的加入对沸石的孔结构、酸性质均起到了一定的调变作用.该沸石具有发达的呈梯级分布的多级孔结构, 孔容高达0.67 cm3·g-1, 且具有较强的Bronsted酸和适度分布的Lewis酸, 大大改善了反应物和产物分子的扩散和反应性能. 在混合C4烃的催化裂解反应中, 该沸石与传统方法合成的β沸石相比, 其转化率提高了约15%, 烯烃(乙烯和丙烯)产率提高了近10%, 芳烃(苯和甲苯)产率提高了3%.

Direct Synthesis and Characteristics of NH4-βZeolite with Hierarchical Pore Structure

NH4-βzeolite with hierarchical porous structure was directly prepared in a nearly neutral synthetic systemusing nonionic compound (polyoxyethylene nonyl phenylether) as the mesoporogen and fluoride as a mineralizer. Samples were characterized by powder X-ray diffractometry (PXRD), scanning electron microscopy (SEM), NH3-temprature programmed desorption (NH3-TPD), N2 adsorption/desorption and differential thermogravimetry (DTG). N2 analysis results showed that the synthesized H-(NH4)-βzeolite contained stepwise distributed micro-mesoporous structure. The Barrett-Joyner-Halenda (BJH) method of analyzing the N2 adsorption isothermshowed that the mesopore volume was 0.67 cm3·g-1 and the most probable pore size was about 21.8 nm. This value was higher than that for the conventional H-βzeolite (0.37 cm3·g-1 and 3.8 nm). The large amount of Lewis acid and the moderate amount of Bronsted acid in the H-(NH4)-β zeolite was examined by means of Pyridine-IR spectroscopy. Compared to conventional H-βzeolite, the conversion in the catalytic cracking reaction of mixed C4 hydrocarbons using this H-(NH4)-βzeolite was improved by 15%. Yields for the olefins (ethene and propene) and aromatic hydrocarbons (benzene and toluene) increased by 10%and 3%, respectively.