Propane dehydrogenation to propylene on metal-containing MFI-type zeolite catalysts

Abstract

The investigation of propane dehydrogenation was made on An-containing MFI type catalysts. Zn was introduced by either ion-exchange, Zn/MFI, or incorporation with the presence of Al to the zeolite framework, An,Al-silicate. It has been found that the host zeolite with ammonium form to which Zn was introduced exhibited higher catalyst performance for propane dehydrogenation than its protonated form (H-form). Thus the comparison between Zn/NH4-MFI and NH4-Zn,Al-silicate was focused and the optimum amount of Zn for each one was investigated. The conversion of propane increased with the increasing amount of Al suggesting that the high acidity of catalyst was obtained. However, the high acidity can readily convert the propylene formed to aromatics and hence the lower selectivity for propylene. When compared on the catalyst stability, Zn/NH4-MFI exhibited higher stability than did NH4-Zn,Al-silicate. The results obtained lead to the conclusion that Zn in Zn/NH4-MFl can prevent the hydrogenation of light olefins to light paraffins such as ethane better than did Zn in NH4-Zn,Al-siilicate. The less hydrogenation of light olefins to light paraffins means the better hydrogen conserved for hydrogen transfer to the carbonaceous deposit on the catalyst surface that responsible for the long catalyst life.