Design and synthesis of Pt catalyst supported on ZSM-22 nanocrystals with increased accessible 10-MR pore mouths and acidic sites for long-chain n-alkane hydroisomerization

Synthesis of ZSM-22 with more accessible 10-membered ring (10-MR) openings is important for the preparation of highly active and selective hydroisomerization catalyst. Herein, we synthesized ZSM-22 nanocrystals (HZSM-22-NA) with more 10-MR openings and a mesoporous structure on a large scale. The prepared Pt/HZSM-22-NA catalyst (4.74 × 10−6 mol·g−1·s−1) exhibited higher intrinsic activity than conventional HZSM-22-supported Pt catalyst (Pt/HZSM-22, 2.65 × 10-6 mol·g−1·s−1) in the hydroisomerization of n-dodecane. Additionally, Pt/HZSM-22-NA had higher C12 isomer selectivity (93.5%) and lower cracking selectivity (6.5%) than Pt/HZSM-22 (79.8% and 20.2%) at the same n-dodecane conversion level (~90%). These features could be due to the change in the porous structure and acidity between HZSM-22-NA and HZSM-22. HZSM-22-NA composed of nanocrystals at c-axis could double the number of accessible 10-MR openings and acidic sites, thus enhancing the isomerization activity of Pt/HZSM-22-NA. Furthermore, the mesoporosity of HZSM-22-NA facilitated mass transfer of the intermediates and products, thus inhibiting cracking reaction.