Durable Copper and Iron SCR Catalysts for Mobile Diesel and Dual-Fuel Applications 2016-01-2214
The latest emission regulations for mobile and stationary applications require the use of aftertreatment methods for NOx and diesel particulate filters (DPF) for particulate matter (PM). SCR catalysts were evaluated by laboratory experiments and the most promising SCR catalysts were also scaled up to full-size. Development with copper (Cu) and iron (Fe) on zeolitic materials (Beta, ZSM-5, SAPO, chabazite) has resulted in the new generation of thermally durable SCR (selective catalytic reduction) catalysts, which have also an improved sulfur tolerance and a low N2O formation tendency. Opposite to Cu on Beta and ZSM-5, Cu on chabazite and SAPO showed clearly lower N2O formation. Cu-SCR catalysts had a low dependency on NO2/NOx but Fe-SCR catalysts required a higher NO2/NOx ratio (>0.3) to keep a high NOx efficiency. The decomposition of sulfates on the durable Cu- and Fe-SCR catalysts was investigated by temperature programmed oxidation (TPO) and reduction (TPR) methods to find the appropriate conditions for desulfation.
Full-scale SCR systems with diesel oxidation catalysts (DOC) were evaluated by engine bench experiments. The Cu-SCR based catalysts showed a wide operation window, resulting in NOx conversions above 95% as fresh and thermally aged at 650-750°C. The platinum containing ammonia slip catalyst (ASC) is usually integrated as a short zone on the SCR unit and its main role is to prevent slip in transient conditions.