Design of Durable Vanadium - SCR Catalyst Systems for Heavy - Duty Diesel Applications 2013-26-0049
The emission regulations for mobile applications become stricter in Euro-IV to Euro-VI levels. Carbon monoxide and hydrocarbon can be removed by efficient Diesel Oxidation Catalysts (DOC) but Particulate Matter (PM) and NOx are more demanding requiring the use of active methods (urea-SCR and DPF) which will be world-wide implemented in the 2010's.
Durable, coated V-SCR catalysts are based on stabilized raw materials and tailored preparation methods. Coated V2O5/TiO2-WO3 catalysts (ceramic 300/400 cpsi and metallic 500/600 cpsi) were evaluated by laboratory and engine bench experiments. Traditional V-SCR catalysts are durable up to about 600°C and have a high efficiency at 300°C-500°C. SCR activities were tailored to be higher also at 200°C-300°C or 500°C-600°C. The use of thermal stabilizers or the vanadium loading variation enabled the changes in operation window and stability. The stabilized V-SCR catalyst kept the SCR activity also after ageing at 600°C-650°C when the reference lost partly the activity. NOx conversions (DOC+SCR, 300 cpsi ceramic) without NH3 slip were above 95% in steady engine points (250°C-530°C, 19.000-51.000 h−1). DOC with a low Pt loading (25 g/cft) was efficient to reach target NO2 promotion (>30% NO2 at 250°C-300°C) needed at low temperatures. The promotion by hydrolysis catalysts on SCR was demonstrated by full and partial flow designs. The development for hydrolysis catalyst coating resulted in lower HNCO formation and better SCR selectivity.
The NOx conversions with defined NH3 slip (<10-20 ppm) by catalyst volumes and controlled urea dosing were used for dosing strategy design over the life-time (>500.000 km) of the system. The target NOx conversion (80%-95%) has a crucial effect on required catalyst volumes and dosing strategy marginal, which principles were analyzed based on urea-dosing experiments.