Iridium/H-ZSM-5 zeolite catalyst promoted via hydrochlorination or hydrofluorination for the hydroconversion of cyclohexene
The hydroconversion of cyclohexene (CHE) was carried out in a flow reactor at atmospheric pressure and temperatures of 50–400 °C using: Ir/H-ZSM-5, Ir/H-ZSM-5(HCl), and Ir/H-ZSM-5(HF) catalysts. The acid site strength distribution, Ir dispersion, XRD, SEM photography for these catalysts were evaluated. The hydroconversion reaction steps of CHE were found to proceed as follows: CHE → cyclohexane; CHE → methylcyclopentenes (MCPEs) → methylcyclopentane (MCPA); CHE → cyclohexadienes (CHDEs) → benzene; benzene → alkylbenzenes; CHE and others → hydrocracked products.The doping of Ir/H-ZSM-5 catalyst with HCl enhanced its acid sites number and strength but reduced the Ir metal dispersion, whereas doping with HF enhanced acid sites number and strength as well as Ir metal dispersion. The hydrogenation step of CHE to CHA was significantly inhibited via HCl doping of Ir/H-ZSM-5 because of agglomeration of Ir crystallites, but significantly enhanced via HF doping due to improving Ir dispersion and increasing acid sites number and strength of the catalyst. Also, MCPEs hydrogenation and CHE dehydrogenation were highest on the untreated Ir/H-ZSM-5 catalyst because it doesn’t suffer diffusion limitation caused by deposited halo-aluminium debris. CHE isomerisation does not critically depend on acid site parameters or on Ir dispersion in the catalysts. Hydrocracking reactions were more active on the HCl treated catalyst.
Journal: Applied Catalysis A: General - Volume 303, Issue 2, 28 April 2006, Pages 141–151