n-Octane aromatization on Pt supported on novel zeolites

Abstract

KL zeolites with cylindrical shape are effective catalyst supports for noctane aromaticzation, but the effectiveness strongly depends on the channel length of the zeolite crystallite as well as Pt dispersion and location of the Pt cluster. The different Pt/KL catalysts in the series were compared in the aromatization of n-octane at 500C and atmospheric pressure. It was found that the catalysts with shorter channel length exhibited improved activity, selectivity, and catalyst life. In addition, the catalysts with shorter channels had a much lower extent of secondary hydrogenolysis. Consequently, more C8 aromatics are preserved in the product and less benzene and toluene are produced compared to the catalysts with longer channels. In the case that the inactive metal was added into Pt/KL catalysts, it was found that the addition of tin improved the stability of the Pt/KL catalyst by inhibiting the adsorption of dehydrogenated species which is the intermediate for formation of coke. Furthermore, the selectivity to C8-aromatics products is increased but the secondary hydrogenolysis reaction, which occurred inside the pore of KL zeolite, is decreased. In addition, it was found that Co1Pt1Sn prepared by vapor phase co-impregnation method yielded a high fraction of alloy phase compared to Seq1Pt1Sn and Seq1Sn1Pt which were prepared by vapor phase sequential impregnation method. As a result, Co1Pt1Sn gave the highest activity and C8-aromatics selectivity among the Pt-Sn catalysts investigated. Moreover, it was observed that OX molecules were produced more compared to without addition of tin because of electronic effect. As a result, the EB/OX ratio was lower than unity.