碱酸联合处理H-ZSM-5沸石多级孔改性

摘要

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.%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。