Comparison of catalytic consequences of ionic liquid-templated ZSM-22 and ZSM-5 zeolites in propene dimerization

Abstract

The ionic liquid-templated TON- and MFI-type zeolites having 10-membered rings were synthesized and their catalytic performances on propene dimerization were studied. The comparable acid site strength among TON- or MFI-type zeolites accounted for the nearly identical propene dimerization turnover rates despite their different Si/Al ratios. At the low propene conversion (<5%), the TON- and MFI-type zeolites (with a Si/Al ratio of 30–120) obtained a dimer selectivity of over 70% and less than 42%, respectively. The different channel structures and acid properties of zeolite were responsible for the different catalytic selectivity in TON- and MFI-type zeolites. Compared to MFI zeolite, TON with a smaller void size was much more suitable for stabilizing the transition states and intermediates for dimers under the reaction conditions. In addition, a three-stage and a three-in-one dimerization reaction pathways were proposed for the ZSM-22 and ZSM-5 zeolites, respectively. • Ionic liquid-templated ZSM-22 and ZSM-5 with various Si/Al ratios were compared. • ZSM-22 showed a higher dimer selectivity over ZSM-5 at high conversion (<70%). • Topological and acidic properties of zeolites are crucial for dimer selectivity. • The turnover rate was shown to be independent of the Brønsted acid concentration.