Microkinetics for toluene total oxidation over CuO–CeO2/Al2O3

• Reaction network and microkinetic modeling.
• Transient response techniques.
• Kinetically significant steps for toluene total oxidation.
• Optimum catalyst composition.

Total oxidation of toluene over a CuO–CeO2/Al2O3 catalyst was studied by means of Temporal Analysis of Products (TAP) at temperatures of 723–873 K in the absence and presence of oxygen (molar toluene:oxygen ratio = 1:9) at degrees of reduction of the catalyst up to 0.42. A single set of kinetic parameters corresponding to the steps of the detailed mechanism can describe the experimental data. A detailed mechanism with oxidation occurring on Ce3+ sites and reduction on Cu2+ sites formed the basis of a microkinetic model. The interaction of reactants and products with the catalyst support was taken into account.A distinction was made between O atoms at the surface of the catalytically active phase and those in the bulk. Transport of the latter to the surface was explicitly accounted for in the model. The abstraction of hydrogen atoms leading to the formation of water is the fastest process. The formation of carbon dioxide occurs through three kinetically significant steps. The potentially slowest step in the whole process was found to be the destruction of the aromatic ring. A linear dependency of the activation energies of the processes which include transport of oxygen from the bulk to the catalyst surface, on the degree of reduction of the catalyst was found.Analysis of the dependency of the catalytic behavior on the catalyst descriptors provided information about the optimum catalyst composition and fraction of the active component exposed, which can be used for catalyst optimization.

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