Effects of channel structure and acidity of molecular sieves in hydroisomerization of n-octane over bi-functional catalysts

SAPO-5, -11, -31, -41, -34, ZSM-5, -22 and -23 were synthesized by using the hydrothermal method and characterized by various methods such as XRD, SEM, XRF and TPD of NH3. They are representative of large-pore, medium-pore, small-pore, weak acid, strong acid, monodimensional channel and zigzag channel type of molecular sieves. Effects of pore size, the number of acid sites over medium-pore SAPOs, acid strength and shape of medium-pore channel on hydroisomerization of n-octane were examined over Pt-loaded corresponding molecular sieves. These results indicate that the selectivity to isomerization in hydroisomerization of n-octane is highly influenced by channel structure in molecular sieves and the conversion activity of n-octane is dependent on acidity of molecular sieves. Monodimensional medium-pore molecular sieves are ideal catalytic materials for higher isomerization selectivity in hydroisomerization of n-octane regardless of acid strength, such as SAPO-11, -31, -41, ZSM-22 and -23.