Toluene Oxidation in the Absence and Presence of CO, CO₂, Water and H₂ over ZrO₂-Based Gasification Gas Clean-Up Catalysts

Gasification of biomass is an environmentally friendly way to produce electricity and syngas when combined with effective gas cleaning. ZrO₂-based catalysts have been proven to remove undesired tar molecules when a convenient amount of oxygen is added. However, high activity in the tar oxidation is not the only requirement for the catalyst performance. The valuable gasification gas components, such as CO and H₂, must be protected while passing the complex gasification gas over the catalyst. Oxidation of toluene as a tar model compound was addressed by applying temperature-programmed surface reaction (TPSR) experiments with continuous feed of toluene, oxygen and one main gasification gas component (CO, CO₂, H₂ or water) over pure and doped zirconias. The most water tolerant catalyst was pure ZrO₂ and the least was SiO₂-ZrO₂. A new indicator called ‘Preferentiality’ was introduced and it expresses in one single quantity how well the catalyst is performing in tar conversion while protecting the valuable components of the gas. At 600 °C, the highest preferentiality of toluene oxidation over both CO and H₂ oxidation was achieved over pure ZrO₂.