Sorptive property dependence of catalytic performance in o-xylene isomerization over H/Ga-ZSM-5

Abstract

The sorptive properties of a synthetic zeolite of type MFI with different concentration and nature of framework cations were studied using different probe molecules. The influence of the framework composition on the BET surface area and micropore void volume was examined using low-temperature nitrogen sorption. Sorption uptake kinetics using different probe molecules such as water, n-hexane, cyclohexane, o-, m- and p-isomers of xylenes, n-butylamine and tributylamine were also studied. The catalytic performance of different MFI isomorphs was studied in the o-xylene isomerization reaction. The probable correlation between the sorptive and catalytic properties has been discussed as a function of framework composition, acidity, o-xylene feed rate calculated in terms of mol/min g of catalyst and reaction temperature. The trend in the para selectivity was found to be proportional to the relative sorption of xylenes. In comparison to H/Al-ZSM-5, H/Ga-ZSM-5 with an almost identical framework composition exhibited lower para-selectivity. Even though all these zeolite catalysts possess identical frameworks consisting of 10-MR openings and intersecting channels, differences in the nature and concentration of the trivalent framework cations, the crystallite size and total acidity lead to changes in their sorptive properties and catalytic performance.