A New Class of Environmental Friendly Vanadate Based NH 3 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 NH 3-SCR technique uses either V 2O 5/WO 3-TiO 2 or Zeolite based catalysts, NOx being continuously reduced by NH 3 resulting in the selective formation of nitrogen and water. A major drawback of V 2O 5 based formulations is their lower thermal stability and low temperature activity, in addition, V 2O 5 release poses serious environmental and toxicity problems. In active filter regeneration performed by post-injection of fuel the temperature may increase up to 800\ub0C resulting in drastic loss of activity (due to poor stability of V 2O 5 based formulations) as well as discharge of V 2O 5. Zeolite-based catalysts promoted by transition metal such as Fe and Cu represent an excellent solution to overcome the stability problems of V 2O 5-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 V 2O 5 in SCR catalyst providing i) good activity in the low temperature window (180\ub0C-300\ub0C) ii) high temperature stability up to 850\ub0C, with no major associated activity loss, iii) absence of toxicological and environmental concern