A New Class of Environmental Friendly Vanadate Based NH₃ SCR Catalysts Exhibiting Good Low Temperature Activity and High Temperature Stability

For the removal of NOx from the oxygen-rich diesel exhaust in mobile applications the selective catalytic reduction (SCR) is one of the most favoured technologies. Well established NH₃-SCR technique uses either V₂O₅/WO₃-TiO₂ or Zeolite based catalysts, NOx being continuously reduced by NH₃ resulting in the selective formation of nitrogen and water. A major drawback of V₂O₅ based formulations is their lower thermal stability and low temperature activity, in addition, V₂O₅ release poses serious environmental and toxicity problems. In active filter regeneration performed by post-injection of fuel the temperature may increase up to 800°C resulting in drastic loss of activity (due to poor stability of V₂O₅ based formulations) as well as discharge of V₂O₅. Zeolite-based catalysts promoted by transition metal such as Fe and Cu represent an excellent solution to overcome the stability problems of V₂O₅-based catalysts with only a small activity penalty and cost raise issues but may show disadvantages in stability after hydrothermal ageing. In the present study a new class of rare earth modified Fe vanadates are shown to be valid substitutes of V₂O₅ in SCR catalyst providing i) good activity in the low temperature window (180°C-300°C) ii) high temperature stability up to 850°C, with no major associated activity loss, iii) absence of toxicological and environmental concern.