Design and synthesis of Pt/ZSM-22 catalysts for selective formation of iso-Dodecane with branched chain at more central positions from n-Dodecane hydroisomerization

Abstract

The formation of centrally branched iso-dodecane was controlled by absorption modes of alkene intermediates on ZSM-22, which included pore mouth type and key lock type. In this paper, we have designed and synthesized two kinds of ZSM-22 catalysts for selective formation of iso-dodecane with branched chain at more central positions from n-dodecane hydroisomerization. Aluminosilicate ZSM-22 was modified via carbonization of template to block the micropores and borosilicate ZSM-22 was synthesized. The characterization results and performance evaluation validated that micropore blockage could limit the pore mouth type at low reaction temperatures which favored the formation of iso-dodecane with side chain near the end of the carbon chain. Owing to the weak acid strength, higher temperatures, which favored the key lock mode, were needed to run the n-dodecane hydroisomerization over Pt/borosilicate ZSM-22. Both the two strategies for catalyst design achieved key lock adsorption mode and improvement of the selectivity for centrally branched iso-dodecane. Most importantly, weak acid sites on borosilicate ZSM-22 could catalyze double-bond isomerization reactions, which enhanced centrally branched iso-dodecane distribution up to more than 47%. Our research provides a prospective strategy for selective formation of centrally branched iso-alkanes and Pt/borosilicate ZSM-22 is expected to have potential applications in n-alkane hydroisomerization.