硅铝比对ZSM-5分子筛催化甲醇制烯烃性能的影响

摘要

The pore structures and acidic properties of the ZSM-5 zeolites with different n(SiO2)/n(Al2O3) were characterized by nitrogen adsorption-desorption, XRD and NH3-TPD. The catalytic performances for conversion of methanol to light olefins (MTO) in a fixed bed packed the different zeolites were evaluated. The effect of surface properties and pore structure of the ZSM-5 zeolites on the catalytic performances for MTO reaction were discussed. The results showed that with the increase of n(SiO2)/n(Al2O3) of ZSM-5 zeol-ites, the average pore diameter of the catalyst decreased, the semi-strong acid gradually disappeared, the acid strength gradually decreased, the selectivity of light olefins and the stability of the catalyst gradually increased. The ZSM-5 zeolite with n(SiO2)/n(Al2O3) of 360 had the weakest acidic property, the smallest average pore size and the largest specific surface area, which made it had the highest total selectivity of ethylene and propylene (up to 69.36%).%以n(Si)/n(A1)分别为25、38、50、80、360的ZSM-5分子筛为催化剂，利用N2吸附-脱附、XRD和NH3-TPD对催化剂的孔结构和表面酸性进行表征分析，测定催化剂对甲醇制低碳烯烃(MTO)各产物的选择性，讨论催化剂的孔结构与表面酸性对其催化性能的影响。结果表明，随硅铝比增加，催化剂平均孔径逐渐减小，中强酸逐渐消失，酸强度逐渐减弱，烯烃的选择性逐渐增大，催化剂的稳定性逐渐增强。其中，硅铝比360的分子筛具有最低的表面酸强度，最大的比表面积和最小的孔径，MTO催化性能最佳，乙烯+丙烯的选择性达69.36%。