Abstract: A series ZSM-5 zeolites with a silicon-to-aluminum atomic ratio of 20 - 150 were applied to systematically study the effects of proton acid sites on the catalytic performance of i-butane and 1-butene. The relationships between the quantity of proton acid site and product distributions and reaction pathways of i-butane, 1-butene, and their mixtures with different ratios were investigated in the temperature range of 400–600 oC, respectively. In the case of long residence time of reactants, the number of proton acid sites affects the depth of the secondary reaction. For i-butane, the reaction is initiated by the protonation and monomolecular cracking, and whereas for 1-butene, the reaction is initiated by the tandem bimolecular pathway of olefin isomerization, polymerization, and hydrogen transfer. For the mixture of i-butane and 1-butene, the reaction still follows the bimolecular pathway, and the product composition is distributed between that of i-butane and 1-butene. This work demonstrates that a reasonable combination of proton acid sites and reaction conditions is necessary to adjust the reaction pathways and product distributions of the C₄ component.

Key words: C₄ component, ZSM-5 zeolite, Br?nsted acid site, monomolecular cracking, bimolecular pathway