ZSM-22 Synthesized Using Structure-Directing Agents of Different Alkyl Chain Lengths for Controlled n-Hexadecane Hydroisomerizations

ZSM-22 zeolites were synthesized using different structure-directingagents (SDAs) with varying alkyl chain lengths, including n-alkyldiamines (DAB, DAH, DAO, and DAD) and lauryl amine(LA). The characteristics of the resulting samples (denoted as "Z-SDA")revealed that optimal elongation of SDA alkyl chains brought abouta decrease in crystallization time while retaining ZSM-22 crystalphase stability. The morphology and acidity of the samples variedas the alkyl chain length of the SDAs increased. The average crystallength ranged from 13 & mu;m to 250 nm, and the total acid contentshowed a downward trend, while each sample possessed nonlinear acidsite distributions. Additionally, ZSM-22-supported Pt catalysts wereobtained and probed using the n-hexadecane hydroisomerizationprocess. It was found that the activity and i-hexadecaneselectivity gradually increased with the alkyl chain length of theSDAs (C-4-C-10). Notably, Pt/Z-DAD achieved>70% yield under specific reaction conditions, which could be attributedto the abundant mesopore network and high proportion of weak Bronstedacid site distributions.