Effect of Hydrohalogenation of Metal/Zeolite Catalysts for Cyclohexene Hydroconversion II. Rhenium/H-ZSM-5 Catalysts

A post-preparation treatment of the Re/H-ZSM-5 catalyst with HCl or HF was performed, and its effect on cyclohexene hydroconversion reactions at 50-400 °C in a continuous flow reactor was investigated. The HF treatment significantly improved the catalytic activity for cyclohexene hydrogenation to cyclohexane and methylcyclopentenes to methylcyclopentane in comparison to the HCl treatment. This is principally attributed to the higher Re dispersion and enhancement of the acid site number and strength. Thereupon occurs the highest hydrocracking activity and the lowest dehydrogenation activity for cyclohexene to cyclohexadienes on Re/H-ZSM-5(HF) by virtue of the highest strength of acid sites. The untreated Re/H-ZSM-5 catalyst exhibited the highest dehydrogenation activity for aromatics production, which may be attributed to the lowest quantity of extraframework Al and Si depositing in the pores and cavities of the zeolite support. Industrially, the relative amounts of xylene isomers produced on the hydrohalogenated catalysts are of interest. The amount of p-xylene was higher than m-xylene on the HF-treated catalyst; m- and p-xylenes presented almost equal values on the HCl-treated catalyst; m-xylene exceeded p-xylene on the untreated catalyst. O-xylene was almost equal to the sum of p- and m-xylenes in all cases.