Synthesis of ZSM-23 zeolite with dual structure directing agents for hydroisomerization of n-hexadecane

Highly crystallized ZSM-23 zeolite samples were synthesized by employing the dual structure directing agents pyrrolidine (PY) and isopropylamine (IPA). The existence of two types of structure directing agents widened the synthesis composition ratio range and speeded up the crystallization. The samples obtained showed larger micropore surface areas and volumes compared with the products synthesized with single SDA. It was found that the use of the dual-structure directing agent had no effect on the total acidity but altered the acid site distribution where more weak and medium acidic sites were exposed and was found to be more suitable for n-hexadecane hydroisomerization. The bifunctional catalysts prepared from the supports using the dual-structure directing agent showed excellent catalytic performance under certain reaction conditions. It was noteworthy that Pt/PI-200 (Pt supported on the dual-structure directing agent with a SiO2 /Al2O3 ratio of 200) showed a constant selectivity to iso-hexadecane ca. 69% with contact time of 0.75 min and longer.