Strong and Weakly Acidic OH Groups of HY Zeolite into the Different Routes of Cyclohexene Reaction: An IR Operando Study

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IR operando study of cyclohexene reaction on HY zeolite (Si/Al = 15) was performed to determine the role of the OH groups located in the different zeolitic cages and the silanol groups (SiOH). A parallel between the product yield and type and amount of OH groups poisoned by coking and pyridine pulses was established. The role of silanol and zeolitic OH groups during cyclohexene conversion and the coverage rate of surface groups of the dealuminated HY zeolite, were evaluated by FT-IR operando study. At the beginning of the reaction, zeolite exhibited a very intense deactivation due to coke formation. Coke is initially deposited on strong acid sites, inhibiting the H-transfer activity. Further, coke formation decreased. At this stage of the reaction, pyridine addition markedly decreased the isomerization activity. In parallel, it is noted that mainly SiOH, OH groups at hexagonal prisms, and perturbed OH groups in sodalite cages were mainly affected, indicating that these groups are responsible for the isomerization steps. These results showed that even weakly acidic sites are active sites for isomerization reaction. In cyclohexene conversion, hydrogen transfer occurs on supercage OH groups of HY zeolite. In contrast, perturbed sodalite OH and hexagonal prisms OH, as well as SiOH groups, are responsible for isomerization steps, as revealed by pyridine pulse addition during the reaction.