The preparation of hierarchical ZSM-48 zeolite-supported bifunctional catalysts for n-hexadecane hydroisomerization

Hydroisomerization plays a significant role in improving the low-temperature fluidity of diesel fuel, producing gasoline with a high-octane number, and lowering the pour point of lubricating oil. Therefore, the development of hydroisomerization catalysts is crucial. Herein, two steps are utilized to this end for synthesizing a hierarchical ZSM-48 zeolite (Z48–0.2CA) continuously: the growth modifier cetyltrimethylammonium bromide (CTAB) is utilized first to limit the growth of ZSM-48 crystals and introduce rich intercrystalline mesopores. Then, the nano-ZSM-48 crystals are treated with citric acid to form intracrystalline mesopores. Furthermore, the acidity of the synthesized Z48–0.2CA is effectively reduced. The test of the catalytic performance of n -hexadecane hydroisomerization over the Pd-loaded Pd/Z48-CA bifunctional catalysts demonstrates that the Pd/Z48–0.2CA catalysts prepared with a CTAB/Al mole ratio of 0.2 and treated with citric acid has the highest iso ‐hexadecane yield of 68.8 %, which is 12.0 % greater at lower reaction temperature in contrast to the conventional microporous Pd/Z48 catalyst because of the improved diffusion of hydrocarbons in the channel of the zeolite and the increased C Pd /C H + value. Therefore, the use of a growth modifier and acid treatment for the synthesis of hierarchical zeolite effectively enhances the catalytic performance of bifunctional catalysts. • The employment of CTAB and further acid treatment is effective for the synthesis of hierarchical Z48-0.2CA sample. • The synthesized Z48-0.2CA sample indicates the largest HF value due to the introduction of more mesopores. • The decrease of framework Al atoms at T1, T3 and T4 sites leads to the reduced Brønsted acid density of Z48-0.2CA sample. • The Pd/Z48-0.2CA catalyst reveals the best catalytic performance due to its largest HF value and the highest C Pd /C H + value.