Kinetics of n-hexane hydroisomerization over HZSM-5 supported platinum catalysts. Features of the process mechanism and the Ni-promoting effect

Abstract

• Bimetallic platinum-containing zeolites are effective catalysts for the paraffins isomerization • The presence of Ni in Pt/HZSM-5 reduces the particle size of the active phase and its stability • The introduction of Ni into Pt/HZSM-5 significantly increased the rate of hydroisomerization • The mechanism of hydroisomerization of n-hexane assumes the direct participation of hydrogen in the skeletal rearrangement • The increase in the rate of isomerization of n-hexane from the hydrogen content is close to linear Kinetic studies of the hydroisomerization of n-hexane under stationary and non-stationary conditions for Pt/HZSM-5 catalysts promoted and non-promoted with nickel have been carried out. The catalysts were studied by the low-temperature N 2 adsorption-desorption, X-ray diffraction, transmission electron microscopy, TPR-H 2 , and TPD-NH 3 methods. It is found that the kinetic equation of n-hexane isomerization on both catalysts is written by a common fractional-rational equation, in which the hydrogen exhibits a positive effect on the reaction rate. However, the values of the kinetic constants of the reaction on the two catalysts differ, showing the influence of the Ni additive on the catalyst properties and the reaction kinetics. The introduction of Ni into Pt/HZSM was accompanied by a decrease in the particle size of the active phase, an increase in the concentration of adsorbed hydrogen, which significantly increased the rate of hydroisomerization. In addition, the distinctive characteristics of the kinetic model of the reaction on the Pt-based and the Pd-based catalyst were elucidated.