Passive NOx Reduction with CO Using Pd/TiO2/Al2O3 + WGSR Catalysts Under Simulated Post-Euro IV Diesel Exhaust Conditions

Abstract

This study deals with diesel DeNO(x) catalysis by physically mixed Pd/TiO2/Al2O3 and water-gas-shift reaction (WGSR) catalysts under CO-rich conditions at a CO/NOx ratio of 16. In the post-Euro IV era, many diesel engines are expected to produce CO-rich exhaust emissions due to the trend toward emission regulation and limitations in related technologies. Under these circumstances, the passive DeNOx strategy utilizing CO as a single reductant can be considered appropriate. The Pd/TiO2/Al2O3 catalyst is well known for its high DeNO(x) performance when CO and H-2 are available as NOx reductants. However, when CO is used as a single reductant, the catalyst shows poor DeNOx activity, even if the CO concentration is exceptionally high (CO/NOx = 16). In this study, the DeNO(x) activity of Pd/TiO2/Al2O3 was noticeably improved by physically mixing it with a proper WGSR catalyst (Cu/ZnO/Al2O3), which is capable of producing H-2 and feeding it to Pd/TiO2/Al2O3 successfully even in the presence of O-2. The NOx conversion exceeded 70% at 400-450 degrees C using a Pd/TiO2/Al2O3 + Cu/ZnO/Al2O3 catalyst mixture at a weight ratio of 33:67. The reaction gas consisted of 500 ppm NO, 8000 ppm CO, 8 vol.% O-2, 5 vol.% CO2 and 10 vol.% H2O and w/f was 0.1 g s/cm(3).