Kinetic models for catalytic reactions from first principles: benzene hydrogenation

Abstract

A fundamental kinetic model was constructed from first principles for the hydrogenation of benzene over a Pt(111) catalyst. Benzene adsorbs at the hollow and the bridge sites of the Pt(111) surface. Benzene at the hollow site is the reactive species, whereas benzene at the bridge site is too strongly bound. Hydrogenation follows a Horiuti–Polanyi mechanism. A reaction path analysis based on quantum chemical density functional theory calculations indicates that the fifth hydrogenation step is the rate determining step with an activation energy of 104 kJ mol−1. From the first principles reaction path analysis, a Langmuir–Hinshelwood–Hougen–Watson rate equation was constructed using first principles kinetic and thermodynamic data. Only the coverage-dependent hydrogen adsorption enthalpy was regressed to accurately (F value of 38 500) model laboratory scale data for the hydrogenation of toluene over a Pt–ZSM-22 catalyst. The optimized hydrogen adsorption enthalpy of −68.8 ± 2 kJ mol−1 is intermediate between the low and high coverage value of −94.0 and −45.0 kJ mol−1 respectively.