沸石Ga-ZSM-5芳构化性能及机理考察

考察了ZSM-5和杂原子分子筛Ga-ZSM-5在正己烷、环已烷及丙烷转化中的催化作用,表明Ga-ZSM-5是良好的芳构化催化剂,它主要以脱氢环化的方式生成芳烃。表征结果及不同预处理条件下Ga-ZSM-5的反应行为表明,Ga-ZSM-5脱镓所形成的非骨架氧化态镓有明显的脱氢活性,Ga-ZSM-5相对较弱的酸性则使其氢转移及裂解反应活性较低。这两者是Ga-ZSM-5具有优良芳构化性能的特征。

Aromatization Properties and Active Phase of ZSM-5 Type Gallosilicate

The conversion of n-hexane, cyclo-hexane and propane on ZSM-5 and ZSM-5 type gallosilicate, Ga-ZSM-5, was investigated and the aromatization properties of the two catalysts were studied. Pure Ga-ZSM-5 is less active than ZSM-5 while degallated Ga-ZSM-5 is quite excellent for the aromatization process. Aromatization on degallated Ga-ZSM-5 is realized mainly via dehydrocyclization whereas that on ZSM-5 is mainly via H-transfer and cyclization. Degallation of Ga-ZSM-5 forms non-skeletal gallium oxide, which, together with the acid, sites on Ga-ZSM-5, can catalyze the dehydrogenation of paraffines and the dehydrocyclization of C_(?)~=—C_(?)~= olefines, thus greatly increasing the activity and selectivity of aromatization. Meanwhile, the relatively lower acidity of Ga-ZSM-5, with respect to that of ZSM-5, corresponds to a lower activity in cracking and H-transfer reaction. As a result, theC_1~0—C_3~0 yield is reduced and the selectivity to aromatics is increased.