Hydroisomerization performance of nanosized high-silica ZSM-48 catalysts synthesized via stepwise crystallization method

In this paper, a nanoparticle-stacked ZSM-48 molecular sieve is prepared by modifying the gel preparation process through stepwise crystallization. The corresponding bifunctional catalyst is developed for the hydroisomerization reaction of n -dodecane. The physicochemical properties of ZSM-48 are characterized and analyzed using XRD, SEM, NH 3 -TPD, N 2 adsorption–desorption and zero-length column (ZLC) method. The crystal size of Z-48-T2 synthesized via the stepwise synthesis method is reduced to as small as 0.6 μm, and its acidity is lower compared to that of Z-48-C. Meanwhile, Z-48-T2 exhibits the highest HF value and demonstrates excellent diffusion properties. Consequently, the Z-48-T2 catalyst shows superior catalytic activity and isomerization selectivity, achieving the highest iso -C 12 yield of 83.8 %. The outstanding diffusion performance of Z-48-T2 results in a monomethyl isomerization yield approximately 21 % higher than that of conventional ZSM-48 molecular sieves. Despite these improvements, the final mono-branched isomer product distribution remains unchanged, with 5-methylundecane being the predominant mono-branched isomer for both Z-48-T2 and Z-48-C.