Tuning the Structure and Acidity of Pt/Hierarchical SSZ-32 Catalysts to Boost the Selective Hydroisomerization of n-Hexadecane

摘要

Developing highly selective and efficient bifunctional catalysts is an important issue for the hydroisomerization of long-chain n-alkanes. It is vital to tailor the balance of isomerization and cracking reactions in hydroisomerization. Herein, a bifunctional Pt/hierarchical SSZ-32 catalyst was fabricated with a sequential desilication-dealumination treatment to boost the selective hydroisomerization of n-hexadecane (C-16). The pore structure and acid sites of SSZ-32 zeolite were tailored. More mesopore and Bronsted acid sites were generated, and the ratio of weak to strong Bronsted acidity (B-w/B-s) was increased by the sequential desilication-dealumination. The generated hierarchical structure had little effect on the selectivity of the reaction pathways of hydroisomerization versus cracking. The ratio of isomers/cracking products increased almost linearly with the increase in the B-w/B-s ratios. Meanwhile, the synergetic effect of the hierarchical structure and acidity regulation promoted the selectivity of monobranched i-C16 products. Therefore, the resulting Pt/SSZ-0.6AS exhibited the highest activity with a total isomer yield of 71.5 at 255 degrees C and the enhanced formation mechanism of monobranched isomers occurred via the pore mouth.