Isomerization of n-butane to isobutane over Pt-modified Beta and ZSM-5 zeolite catalysts: Catalyst deactivation and regeneration

This work addresses the deactivation behavior of H-Beta, H-ZSM-5, Pt-Beta and Pt-ZSM-5 catalysts in the isomerization of n-butane to isobutane. Furthermore, the type of coke formed inside these catalysts was characterized. The regeneration of Pt-Beta and Pt-ZSM-5 with synthetic air was also investigated. Most of the coke was formed during the first 70 min of TOS. Linear long-chain olefins formed the soluble coke, which was mainly determined by the reactant molecule and formed by consecutive oligomerization of n-butane molecules. On the other hand, the amount of insoluble coke is influenced by the reaction conditions, carrier gas and, most of all, zeolite structure. Pt and hydrogen inhibit successive reactions, i.e. alkylation, cyclization, that soluble coke undergoes before becoming insoluble. The beneficial effect of coke on the shape selectivity was observed, which increased the isomerization efficiency, defined as IE = iC₄/(iC₄ + C₃ + C₅). The activity on Pt-Beta was completely restored by oxidative regeneration, showing a higher IE than the fresh one.