Mechanistic Kinetic Models for n-Heptane Reforming on Platinum/Alumina Catalyst

Abstract

The kinetics of the reforming of n-heptane on a platinum/alumina catalyst has been studied in a pulse microcatalytic reactor at a total pressure of 391.8 kPa over a relatively wide temperature range of 420°C–500°C. The differential and integral methods were used for the kinetic analyses of the reforming reaction. Twenty-nine reaction rate equations of the Langmuir-Hinselwood-Hougen-Watson type, based on molecular and atomic adsorption of hydrogen, were developed. Parameter estimates for the n-heptane reforming reactions were obtained by application of the Nelder-Mead simplex optimization technique to the predicted and observed conversion/production rates of the reaction components. Discrimination among rival kinetic models was based upon physicochemical criteria, analysis of the residuals, and statistical and thermodynamic tests. The rate-determining step was found to be the surface reaction of adsorbed iso-heptane to adsorbed methylcyclohexane with dissociative adsorption of hydrogen on the catalyst surface during dehydrocyclization of iso-heptane to methylcyclohexane. Hence, the surface reaction on the metallic function is rate-determining for the n-heptane reforming on the Pt/Al2O3 catalyst.