Synthesis, characterization and isomerization performance of micro/mesoporous materials based on H-ZSM-22 zeolite

•Micro/mesoporous materials were prepared via recrystallization of H-ZSM-22 zeolite.•Recrystallization led to the increase of weak B acid sites at pore mouths.•Recrystallized micro/mesoporous catalysts exhibited superior isomerization selectivity.•The mesoporous layers could remarkably improve the multi-branched isomer selectivity.

Micro/mesoporous materials with different mesoporosities were prepared through recrystallization of H-ZSM-22 zeolite in alkaline solution with cetyltrimethylammonium bromide template (CTAB). The structure, morphology, pore properties, acidity and isomerization performance of the catalysts by using the resulting materials were characterized and assessed. The dissolution and recrystallization procedure introduced the well-developed mesoporous structure of MCM-41 type with the meso-scale channels of about 3 nm in size on the outer surfaces of the microporous H-ZSM-22 zeolites, forming the micro/mesoporous materials, which possessed increased weak B acid sites at the pore mouths and a reduced amount of total acid sites. It is shown that the presence of well-developed mesopores could remarkably improve the selectivity to multi-branched products and suppress the side cracking reactions in n-dodecane isomerization. The micro/mesoporous Pt/ZSM-22/MCM-41 bifunctional catalyst with suitable recrystallization degree exhibits high isomerization selectivity under high conversion in long-chain n-alkane isomerization compared to the original microporous Pt/H-ZSM-22 catalyst.

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