Zn-promoted Hβ zeolite for gas-phase catalyzed aza-heterocyclic-aromatization of acrolein dimethyl acetal and aniline to quinolines

Abstract

Catalytic activities of Zn-promoted Hβ zeolite for gas-phase aza-heterocyclic-aromatization of acrolein dimethyl acetal and aniline to quinolines were investigated. the Zn/Hβ catalyst showed better selectivity to quinoline than the parent Hβ one. Characterization results demonstrated that the Zn/Hβ catalyst prepared via deposition precipitation method existed the isolated Zn2+ cations as well as the highly dispersed ZnO clusters, which not only decreased concentration of strong acid sites but also enhanced enhance aromatization process. As a result, the decrease of strong acid sites restrained the cracking of acrolein to acetaldehyde as well as the alkylation of quinoline to ethylquinoline effectively; and the Zn species of catalyst further improved aromatization process of dihydroquinoline to quinoline. Moreover, the Zn/Hβ catalyst presented relatively enhanced ability of anti-activation and excellent regenerability, owing to decrease strong acid-induced polymerization of active intermediates to form the coking. Under the optimized operating conditions, more than 51 % yield of quinoline was achieved over Zn/Hβ catalyst; which far exceeded quinoline yield (28 %) over the pure Hβ one. Besides, a plausible reaction routes in vapor-phase acrolein diethyl acetal with aniline to quinolines were suggested in this paper.