碱酸联合处理H-ZSM-5沸石多级孔改性

Hierarchical mesoporous modification of H-ZSM-5 zeolites via sequential alkali and acid treatments

采用水热合成和离子交换法制备H-ZSM-5沸石。以硅铝比为47的H-ZSM-5沸石为介孔改性原料,用水热碱预刻蚀—碱溶滤—酸洗处理法制备微孔-介孔材料。采用XRD、N2吸附-脱附、FTIR、SEM、TEM等技术,考察逐级碱酸处理过程和水热碱预刻蚀温度对改性沸石介孔形成、介孔尺度分布和织构性质的影响。实验结果表明,碱酸改性沸石具有较高的比表面积、介孔率和微孔-介孔结构性质,同时较好地保留了H-ZSM-5沸石的骨架结构。升高水热碱预刻蚀温度导致改性沸石的微孔体积、比表面积、相对结晶度和收率逐渐下降,总比表面积增幅由38%降至34%,附加介孔体积与总孔体积的比保持在70%以上。水热碱预刻蚀温度为358 K的HZ-2试样的介孔比表面积和介孔体积最大,分别为209.8 m2/g和0.295 cm3/g,微孔与介孔的体积之和可达0.364 cm3/g。

H-ZSM-5 zeolite with silica-alumina ratio of 47 was prepared by hydrothermal synthesis and ion exchange. Its mesoporous modification was conducted through sequential hydrothermal alkali pre-etching, bulk alkali leaching, acid leaching and ion-exchange. The effects of the sequential treatment process and alkali pre-etching temperature on the mesoporous formation, pore size distribution and textural properties of the modified zeolites were investigated by means of XRD, N2 adsorption-desorption, FTIR, SEM and TEM. The results indicated that the modified zeolites showed relatively high specific surface area, mesoporosity and mesopore-size distribution and kept the framework structure of the H-ZSM-5 zeolite well. The hydrothermally alkali pre-etching temperature rise led to decreasing their microporous volume, specific surface area, relative crystallinity and mass yield, and the incremental specific surface area from 38% to 34%. At the same time, the ratio of mesoporous volume to total micro- and mesoporous volume were kept more than 70%. When the hydrothermal alkali pre-etching temperature was at 358 K, the mesoporous specific surface area and volume of sample HZ-2 were maximum, 209.8 m2/g and 0.295 cm3/g, respectively, while the total micro- and mesoporous volume was 0.364 cm3/g.