Toluene oxidation over ZrO2-based gasification gas clean-up catalysts: Part B. Kinetic modeling

Abstract

Energy, liquid biofuels and chemicals can be produced from biomass via gasification followed by gas cleaning over ZrO2-based catalysts. When a small amount of oxygen is added, ZrO2-based catalysts can be utilized in tar decomposition reactions (tar molecules need to be removed before further use). Oxidation of toluene as tar model compound was studied by temperature-programmed experiments over ZrO2, Y2O3-ZrO2 and SiO2-ZrO2. In the first part of this study (Part A: Effect of oxygen on the formation of primary products), special attention was given to the effect of oxygen amount on the formation of synthesis gas components (CO and H2) from toluene. The data obtained in Part A was extended and subjected to kinetic modeling. As a result, the reaction mechanism of toluene oxidation over ZrO2-based catalysts was discovered. The first step in toluene oxidation is the adsorption of toluene as a benzyl species. Next, the surface benzyl species is oxidized, possibly via superoxide surface species (O2−), into four products in a single net primary reaction. Oxidation of CO and H2 are the secondary reactions in the model. Furthermore, the present study clearly demonstrates the strength of temperature programming as a transient technique for comprehensive mechanistic investigations, kinetic model development and parameter estimation.