On the synthesis of highly acidic nanolayered ZSM-5

Nanolayered ZSM-5 zeolites were synthesized at high framework Al content. Crystallization of ZSM-5 zeolite synthesis gel at Si/Al ratio of 20 at 423 K using C22H45–N+(CH3)2–C6H12–N+(CH3)2–R (R = hexyl or propyl) as structure-directing agents resulted in amorphous product. When the hydrothermal synthesis was carried out at 443 K instead of 423 K, crystalline nanolayered ZSM-5 zeolites were obtained. By replacing the hexyl end group by propyl, the crystallization rate increased due to increased occupancy of the intersections of the MFI framework by quaternary ammonium centers. Optimized hydrothermal synthesis at Si/Al = 20 (443 K, NaF addition) with this surfactant resulted in highly crystalline nanolayered ZSM-5 zeolite. Not all Al atoms are built into the zeolite framework, which limits the overall Bronsted acidity. The catalytic performance in n-heptane hydroisomerization of the various zeolites trends well with the Bronsted acid site density. The product distribution during n-heptane hydroisomerization points to an increased rate of product desorption (higher isomers’ selectivities and increased selectivity of dibranched isomers). The nanolayered ZSM-5 zeolites outperform bulk ZSM-5 zeolite in the methanol-to-hydrocarbons reaction in terms of the methanol conversion capacity.