Reaction of linear, branched, and cyclic alkanes catalyzed by Brönsted and Lewis acids on H-mordenite, H-beta, and sulfated zirconia

Abstract

The isomerization and cracking of pentane, cyclohexane, and C5–C6 branched alkanes (isopentane, 2-methylpentane, 2,2-dimethylbutane, and 2,3-dimethylbutane) were performed on H-mordenite and H-beta at 473 K, and sulfated zirconia at 273 K and 323 K. Pentane and 2-methylpentane were converted into the corresponding isomers on Brönsted acids of mordenite and beta-zeolite in the initial stage of the reaction. The major final product was isobutane, formed by bimolecular reaction in the later stage of the reaction. In contrast, pentane and 2-methylpentane were converted into their isomers by monomolecular reaction on sulfated zirconia with high selectivity. No reaction was observed in isopentane isomerization on sulfated zirconia because the product has the same structure. These highly selective isomerizations are considered to be catalyzed by Lewis acid sites on sulfated zirconia, because it has superacidic Lewis acid sites. Multi-branched alkanes showed higher reactivity than linear, mono-branched and cyclic alkanes. Isobutane formation as the main product and remarkable deactivation were found in the isomerization of 2,2-dimethylbutane and 2,3-dimethybutane on sulfated zirconia. The Brönsted acid sites on sulfated zirconia were not strong enough to promote the skeletal isomerizations of linear and mono-branched alkanes. However, these acid sites were active enough to form intermediates by bimolecular reaction of multi-branched alkanes, and were the source of catalyst poisoning species formed by dehydrogenation. Cyclohexane was converted into methylcyclopentane on both Brönsted and Lewis acid sites with high selectivity.