关键词: ZSM-5, 改性, 芳构化, 反应机理, 催化剂

Abstract: The reaction rules for aromatization of alkanes having various carbon number and structure over Zn-Pt-Re/ZSM-5 catalyst were studied on a continuous flow micro-reactor device and using n-hexane, n-heptane, n-octane, methylcyclohexane and cyclohexane as probe molecules. The aromatization performance of alkane over Zn-Pt-Re/ZSM-5 catalyst and conventional reforming catalyst CB-8 was compared. Test results show that when reaction temperature is less than 450℃, the sequence of generating aromatization reactions from hard to easy is n-hexane, cyclohexane, methylcyclohexane, n-heptane and n-octane; when the reaction temperature is over 450℃, the aromatics yields of alkanes tested are all more than 90％. It is also found that the aromatization mechanism of alkane over CB-8 catalyst and Zn-Pt-Re/ZSM-5 catalyst is different: over CB-8 catalyst, alkane is turned into cycloalkane by dehydrocyclization firstly, followed by further dehydrogenization to form aromatics; over Zn-Pt-Re/ZSM-5 catalyst, two possible reaction pathways may exist, one is the same as over CB-8 catalyst, the other is alkanes crack to form light olefins firstly, followed by reactions including polymerization, cyclization and dehydrogenization to form aromatics, and it seems that the latter is the main one.

Key words: ZSM-5, modification, aromatization, reaction mechanism, catalyst