Hydroisomerization-cracking of gasoline distillate from Fischer–Tropsch synthesis over bifunctional catalysts containing Pt and heteropolyacids

A gasoline distillate from the Fischer–Tropsch synthesis (so-called as F–T gasoline) was collected in a cold trap set in a gas-flowed slurry reaction system. The F–T gasoline contained 92.8 wt.% n-alkanes (ranged from n-C4H10 to n-C14H30), 2.4 wt.% 1-alkenes, and 4.8 wt.% iso-alkanes. By the hydroisomerization-cracking in an atmospheric flowed fixed-bed reactor over the catalysts containing Pt and heteropoly compound Cs2.5H0.5PW12O40 (abbreviated as Cs2.5), the F–T gasoline was converted to gasoline distillated mixed alkanes with a high iso/n ratio. A mechanical mixture of Pt/Al2O3 and Cs2.5 (noted as Pt/Al2O3 + Cs2.5) showed the highest catalytic performance among various catalysts. The product over Pt/Al2O3 + Cs2.5 after 5 h on-steam at 523 K contained 94.4% C5–C9 (gasoline components) with a high iso/n ratio of 8.45. The co-grinding time of Pt/Al2O3 and Cs2.5 influenced the catalytic performance when the time was shorter than 10 min but gave little influence on the catalytic performance when the time was longer than 10 min. Because the iso/n ratio of products over Pt/Al2O3 + Cs2.5 increased by adding Pt in Cs2.5 and decreased with increasing H2/feedstock, the reaction proceeded through a bifunctional mechanism in which Pt sites achieved a hydrogenation/dehydrogenation function and acid sites achieved an isomerization/cracking function. The balance of Pt and solid acids was important to obtain a high catalytic performance in the hydroisomerization-cracking of F–T gasoline. Because Cs2.5 possessed moderate acidic strength and uniformly distributed acidic sites, Pt/Al2O3 + Cs2.5 showed a higher catalytic stability than that over Pt/Al2O3 + SO4/ZO2 and showed a higher catalytic activity than that over Pt/Al2O3 + H-ZSM-5.

► We investigated F–T gasoline hydroisomerization-cracking on bifunctional catalysts.
► Synergy effect of Pt and solid acid is very important for the reaction.
► Mechanical mixed catalyst showed high activity due to small Pt particles.
► Heteropolyacid is suitable for the reaction due to moderate acidic strength.