Pore mouth catalysis promoting n-hexane hydroisomerization over a Pt/ZSM-5 bifunctional catalyst

In hydroisomerization of n-alkane over bifunctional Pt/zeolite, the pore mouth catalysis was inferred to be crucial to selective formation of the target product: isomers. However, the roles of Brønsted acid sites (BASs) locating near the pore mouth region of zeolites (BASpm) are still lacking detailed experimental evidence. Here, it was found that the formation of C6 isomers was much enhanced by locating Pt on γ-Al2O3, apart from the BASs inside the micro-channel of ZSM-5 with excessive concentration of BASs (CBAS). However, such beneficial effects disappeared after passivating the BASpm of ZSM-5. A linear dependence of the yield of C6 isomers on the BASpm was revealed for the designed Pt/Al2O3+ZSM-5. Pore mouth catalysis was thereby provided; in this process, the BASpm acted as the main active sites for isomerization of alkene intermediates, suppressing the undesired acid-cracking reaction occurring inside the microchannel of zeolite.