Hydroisomerization of n-heptane over Pt/USY catalysts promoted by Cr additive

The Pt-supported USY zeolite catalysts doped with Cr, Al or Zn were prepared by impregnation, and characterized by XRD, low temperature nitrogen physisorption, H₂-chemisorption and IR spectroscopy of the pyridine adsorption. Catalytic activities were evaluated via the hydroisomerization of n-heptane with an atmospheric fixed-bed reactor. The Pt dispersion and acidity of the Pt-supported USY catalyst were influenced by the addition of the promoters. The Pt-supported catalysts promoted by Cr, Al or Zn, especially by Cr, were catalytically much more stable and exhibited much higher catalytic activity and selectivity for isomerization of n-heptane than the catalysts without the dopant. Both the conversion and selectivity are discussed in relation with the physicochemical properties of catalysts.