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

摘要

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/NO_x 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 DeNO_x 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 H2 are available as NO_x reductants. However, when CO is used as a single reductant, the catalyst shows poor DeNO_x activity, even if the CO concentration is exceptionally high (CO/NO_x = 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 H2 and feeding it to Pd/TiO2/Al2O3 successfully even in the presence of O2. The NO_x conversion exceeded 70% at 400-450 °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.% O2, 5 vol.% CO2 and 10 vol.% H2O and w/f was 0.1 g s/cm~3.