Deposition and decomposition of urea and its by-products on TiO2 and VWT-SCR catalysts

Exhaust gas aftertreatment devices such as selective catalytic reduction (SCR) catalysts are often positioned close to the combustion engine today. These close-coupled systems lead to rather short mixing sections of the reducing agent urea–water solution (UWS) and the exhaust gas in the case of SCR of nitrogen oxides (NOx) by ammonia. Due to higher temperatures, an increased UWS droplet evaporation is expected. However, startup procedures and unfavorable operating conditions can lead to a stronger impact onto exhaust pipes and the catalysts itself. The interaction of urea and its by-products with TiO2 and V2O5–WO3/TiO2 (VWT), as typical SCR catalyst materials, is investigated via thermogravimetric analysis. A surface reaction mechanism with associated kinetic expressions is developed. Complete decomposition of all deposited species occurs at temperatures as low as 450 °C. This behavior can be well represented by the model developed. •TG experiments of urea by-products and SCR catalyst material.•Investigation of the influence of TiO2 and V on the deposit decomposition.•Development of a surface mechanism and kinetics.•Simulations with multiphase tank reactor model in good agreement with exp. data.