Abstract:

A series of La-modified ZSM-5 were prepared by hydrothermal treatment and incipient wetness impregnation. Compared with those of pristine ZSM-5, an increase in lattice constants and the amount of strong, weak and the total acid cites of La-modified ZSM-5 by the hydrothermal treatment occurs. The amount of acid cites of by La-modified ZSM-5 by incipient wetness impregnation increases, however, the lattice constants does not change. High yields of ethylene and propylene were obtained on both kinds of modified samples tested in the catalytic cracking of hexane. The yields of ethylene and propylene were achieved on the samples modified by hydrothermal treatment at WHSV 6 h^-1 (23.39% of ethylene, 25.17% of propylene), which are 2% and 4% larger than those of the pristine ZSM-5 samples (21.19% of ethylene, 21.04% of propylene), and slightly better than those of the samples modified by incipient wetness impregnation. In the long-term experiment of hexane cracking with at WHSV 4 h^-1, the samples modified by hydrothermal treatment (2000 min) and incipient wetness impregnation (1600 min), exhibited much longer durability than the pristine ZSM-5 sample (800 min). It suggested that the hydrothermal treatment is better modification method in the preparation of La-modified ZSM-5 catalyst to improve the performance of hexane catalytic cracking.

Key words: La modification, hydrothermal treatment, impregnation, ZSM-5, catalytic cracking, catalyst

摘要：

采用高温水热法和等体积浸渍法将La离子负载于ZSM-5分子筛上得到了改性ZSM-5分子筛材料。水热法La改性样品改变了ZSM-5的晶胞尺寸，提升了其强酸、弱酸及总酸量。浸渍法改性样品也提高了其酸量但是对晶胞参数没有影响。将改性样品应用于正己烷催化裂解反应中，两种方法均得到了较高的双烯收率，其中水热法改性样品在空速为6 h^-1时乙烯收率和丙烯收率分别为23.39%和25.17%，这与原样相同空速下的乙烯丙烯收率（乙烯为21.19%，丙烯为21.04%）相比分别提升了约2%和4%，略高于浸渍法改性样品。在长周期反应寿命方面也有了显著提高，在空速为4 h^-1时，水热法改性样品（2000 min）和浸渍法改性样品（1600 min）均显著优于原样（800 min）。这些结果表明采用水热法La改性可以更好地提升ZSM-5分子筛在正己烷催化裂解反应中的性能。

关键词: 镧改性, 水热法改性, 浸渍法, ZSM-5, 催化裂解, 催化剂