Hydroisomerization of n-Hexadecane over Highly Dispersed ZSM-48 Synthesized Using Hexamethylenediamine

Zeolite ZSM-48 is an efficient acidic catalyst support for the hydroisomerization of higher (C16+) n-paraffins, but its industrial application is hindered by the high cost of conventional structure-directing agents (SDAs). This study develops a more economical synthesis method using hexamethylenediamine (HDA) as an affordable SDA. A series of high-crystallinity zeolite samples (SiO2/Al2O3 = 160–200) were synthesized hydrothermally. After loading with 0.5 wt % Pt, their physicochemical properties and catalytic performance were evaluated in the hydroisomerization of n-hexadecane at 3.0 MPa. The initial alkali content in the reaction gel was identified as a critical parameter controlling crystallization selectivity, crystal morphology, and crystallinity. The sample synthesized with low alkali content exhibited the highest performance, achieving 90% n-hexadecane conversion at 320°C with a yield of desired isomers up to 62%. This demonstrates the high potential of HDA for crystallizing selective ZSM-48 and for preparing promising catalysts for the hydroisomerization of higher n-paraffins.