不同硅铝比的ZSM-11沸石分子筛的催化性能

合成了一系列硅铝比为31—176的ZSM-11沸石,以甲苯-甲醇烷基化、间二甲苯异构化和甲苯歧化三个反应作为探针反应,研究了它们的催化性能。将其与酸性质和晶胞参数相关联发现,低硅铝比适于甲苯歧化,中硅铝比适于间二甲苯异构化,高硅铝比适于甲苯-甲醇烷基化反应。各反应所需的酸强度为甲苯歧化>间二甲苯歧化>间二甲苯异构化>甲苯-甲醇烷基化。Na~+的存在以及用4-甲基喹啉或(CH_3)_3SiCl中毒,可抑制强酸位,明显提高甲苯-甲醇烷基化反应生成对二甲苯的选择性,尤以(CH_3)_3SiCl中毒的低Al/u.c.的NaHZSM-11最佳。

CATALYTIC PERFORMANCE OF ZSM-11 ZEOLITES WITH DIFFERENT Si/AI RATIOS

A series of ZSM-11 zeolites with Si/Al ratio from 31 to 176 were synthesized.Their catalytic properties were studied in a pulse micro-reactor by using the alkylation of toluene-metbanol , the isomerization of m-xylene and the disproportionation of toluene as probe reactions. It is found that the HZSM-11 zeolite with low Si/Al ratio is fit for the reaction of toluene disproportionation, and those with middle and high Si/Al ratio are fit for the isomerization of m-xylene and the alkylation. of tolu-ene-metbanol respectively. When the strong acid sites decrease and the crystal cells constrict with the increase of Si/Al ratio, the p-xylene selectivity for the alkylation of toluene-methanol obviously increases, and the p-xylene selectivity of NaHZSM-11 zeolites is higher than that of HZSM-11 zeolites. When HZSM-11 and NaZSM-11 are poisoned by 4-methylquinoline or trimetbylcblorosilicane, the p-xylene selectivity can be greatly increased, particularly, the NaHZSM-11 with high Si/Al ratio poisoned by trimethylchlorosilicane exhibits the excellent catalytic performance for the alkylation of toluene-methanol.