Tailoring the structure and acid site accessibility of mordenite zeolite for hydroisomerisation of n-hexane

• Published in: Applied catalysis. A, General Vol. 562; pp. 159 - 172
• Main Authors: Pastvova, Jana, Pilar, Radim, Moravkova, Jaroslava, Kaucky, Dalibor, Rathousky, Jiri, Sklenak, Stepan, Sazama, Petr
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 25.07.2018; Elsevier Science SA
• Subjects: Accessibility; Acids; Alkanes; Aluminum; Catalysis; Fluorination; Isomerisation; Isomers; Micromesoporous structure; Molecular structure; Mordenite (MOR) zeolites; n-hexane; Organic chemistry; Silicon; Spectrum analysis; Supermicroporosity; Zeolites; Isomerisation; n-hexane; Micromesoporous structure; Supermicroporosity; Mordenite (MOR) zeolites
• ISSN: 0926-860X; 1873-3875
• DOI: 10.1016/j.apcata.2018.05.035

[Display omitted] •The acid sites in mono-dimensional 12-ring channels and 8-ring side pockets of mordenite zeolites are diffusion-restricted.•Concurrent extraction of Si and Al provides 3D supermicroporous zeolite with high accessibility of the acid sites.•The 3D supermicroporous mordenites provide strongly enhanced activity, selectivity and long term catalytic stability.•The concurrent extraction of Si and Al provides supermicroporous zeolites for variety of diffusion-restricted reactions. Mordenite zeolites with diffusion-restricted access to the acid sites located in mono-dimensional 12-ring channels and 8-ring side pockets have found broad applications as catalysts for hydroisomerisation of linear C5 and C6 alkanes and other highly relevant acid-catalysed processes. The accessibility of the porous structure of mordenite (MOR) zeolite is traditionally enhanced by dealumination, but this is invariably connected with a dramatic reduction in the aluminium content and corresponding concentration of the acid sites in the zeolites. Here we describe the preparation of MOR zeolite with high micropore volume, three-dimensional supermicropores (d ∼ 7.5 Å) and good acid site accessibility by concurrent extraction of Si and Al using postsynthesis fluorination-alkaline-acid treatment. The concurrent extraction of Si and Al enables formation of more developed supermicroporous structure and preservation of the molecular Si/Al. The procedure yields MOR with a crystalline structure in which the Si/Al ratio and the micropore volume can be tailored (Si/Al from ∼ 6, VMI up to 0.25 cm3.g−1) by the chemical conditions of the treatment. The Al-rich 3D supermicroporous structure with accessible Brønsted and Lewis active sites provides strongly enhanced activity, selectivity and long-term catalytic stability in the transformation of n-hexane into the corresponding branched isomers.