Resolving kinetics and dynamics of a catalytic reaction inside a fixed bed reactor by combined kinetic and spectroscopic profiling

Abstract

The oxidative dehydrogenation of ethane to ethylene was studied using a MoO₃ based catalyst supported on γ-alumina spheres. The measurement of species and temperature profiles through a fixed bed reactor shows for the first time the reaction pathways inside the catalyst bed directly. Oxidative dehydrogenation of ethane to ethylene and water occurs on the redox sites of MoO₃ only in the presence of gas phase oxygen. Further oxidation of the product ethylene to carbon dioxide occurs as a subsequent reaction step by lattice oxygen of MoO₃. Deep oxidation of ethylene to CO₂ is the only existing reaction in the absence of gas phase oxygen reducing MoO₃ to MoO₂. Oxidation of CO and C₂H₆ by lattice oxygen does not occur. The reduction of the catalyst can be followed by in situ fiber Raman spectroscopy as a function of the oxygen partial pressure. The in situ Raman measurements are complemented by ex situ micro-Raman spectroscopy and X-ray diffraction. The combined measurement of kinetic and spectroscopic reactor profiles presents a novel approach in in situ catalysis research to establish catalyst structure–function relationships under technically relevant conditions of temperature and pressure.