Steam reforming kinetics of olefins and aromatics over Mn-Cr-O spinel oxides

Abstract

Catalytic steam reforming of propylene, benzene and toluene was investigated over Mn-Cr-O spinel oxides with different stoichiometry. The catalysts were structurally stable during reforming conditions except for Mn3O4, which reduced in situ to MnO. The Cr2O3 catalyst showed the highest initial rate for propylene reforming, whereas the Mn-rich Mn1.5Cr1.5O4 spinel was the most active and stable catalyst for aromatic reforming. Reforming rates of olefins and aromatics were comparable under 0.05 bar hydrocarbon and 0.40 bar steam at 873 K. The reforming rate of olefins and aromatics was first order in hydrocarbon and slightly inhibited by H2O, which is consistent with a Mars-van Krevelen type mechanism. Of the hydrocarbons investigated, only the rate of toluene reforming was negative first order in excess H2. Results from diffuse reflectance infrared Fourier transform spectroscopy of adsorbed toluene on a spinel catalyst suggest that H2 inhibits the rapid oxidation of the methyl group of toluene.