On the Formation of Hydrocarbon Chains in the Aromatization of Aliphatic Olefins and Dienes Over High-Silica Zeolites

The Effect of Acidity on Olefin Aromatization over Potassium Modified ZSM-5 Catalysts

“…These messages indicate that the more hydrogen-deficient hydrocarbons, such as diene or cycloolefin undergo aromatization process more easily than alkenes with the same carbon number during olefin aromatization. This is well in agreement with the previous document reported by Isagulitants [7]. It is worth noting that over the 1.9 wt% K/ZSM-5 catalyst, without any strong acid sites, almost no aromatics were formed when using 1-butene as reactant, whereas a large quantity of aromatics was formed when using 1,3-butadiene, isoprene or cyclopentene as reactants, as shown in figure 10.…”

“…The aromatics formed in the liquid products were almost negligible when the K-loading reached 1.9 wt%. Combining the reaction data with the results of NH 3 -TPD, it is reasonable to propose that the strong acid sites are absolutely necessary for the transformation of butene into aromatics, while the interconversion of olefins is catalyzed both by strong and weak acid sites, which is in agreement with earlier reports [4,[6][7][8], which state that the transformation of olefins, methanol and ethanol to aromatics is catalyzed by strong acid sites over the ZSM-5. Figure 4 shows the dependence of aromatics distribution on K-loadings on the catalyst.…”

Optimizing the Acid Properties of the HZSM-5 Catalyst for Increasing the p-Xylene Yield in 1-Hexene Aromatization

“…This is closely related to the acid properties of the catalysts. HZSM-5 was widely used for olefin aromatization due to its variable acid properties. − For increasing the aromatics yield, metals were introduced into the HZSM-5 to strengthen the hydrogen transfer and/or dehydrogenation capabilities by adjusting the acid properties of catalysts. ,, Many in-depth studies have been conducted on the relationship between the mechanism of olefin aromatization and the acid properties of catalysts. ,− The multistep continuous reaction begins with the interconversion of olefins with Brønsted acid sites (BAS) as the active sites, including olefin cracking to form small-molecule olefins (C2–C4) and olefin oligomerization to form large-molecule olefins (C5+). ,, Afterward, the large-molecule olefins are further converted to C6+ dienes by the synergistic interaction of Lewis acid sites (LAS) and BAS, and then the C6+ dienes are cyclized and dehydrogenated to aromatics. , By comparing the results of light hydrocarbon aromatization over a series of zinc-modified HZSM-5 catalysts, Hadrien Coqueblin et al found that an appropriate L/B ratio was the key to obtaining a high aromatics yield. Gao et al measured the number of BAS-Ga pairs by 1 H– 71 Ga double-resonance solid-state NMR and found that the synergic effect between BAS and Ga species strengthened the Brønsted acidity and the number of BAS-Ga pairs correlated with the aromatics selectivity in the MTA reaction.…”