Selective catalytic reduction of nitrogen oxides from exhaust of lean burn engine over in-situ synthesized Cu-ZSM-5/cordierite

ZSM-5 zeolite was in-situ synthesized successfully on the surface of honeycomb cordierite substrate, certified by XRD and SEM techniques. Good thermal and hydrothermal stability of ZSM-5/cordierite could be obtained because of the in-situ synthesis method. Copper ion-exchanged ZSM-5/cordierite was studied as catalyst for selective catalytic reduction of nitrogen oxides. For practical reasons, the catalytic testing experiments were preformed on a real lean burn engine. Unburned hydrocarbons and carbon monoxide in the exhaust were directly used as reductants for NOx reduction. Cu-ZSM-5/cordierite exhibited high catalytic activity, and at 673 K the maximal NOx conversion to N2 could reach 50% at gas hourly space velocity (GHSV) of about 25 000 h(-1). Hydrocarbons and carbon monoxide in the exhaust could also be purified at the same time. As expected, Cu-ZSM-5/cordierite catalyst exhibited good duration and antipoison properties. When traces of lanthanum were introduced to Cu-ZSM-5/cordierite catalyst as a modifier, the activated temperature of the catalyst could be decreased and the temperature window with high NOx conversions broadened. Cu-ZSM-5/ cordierite and LaCu-ZSM-5/cordierite were thought as promising automobile exhaust catalysts under lean conditions. Copper is the main active component in the Cu-ZSM-5/ cordierite catalyst and Cu(II), which was found in the catalyst during the proceeding of reaction by XPS, is thought to be essential. On the basis of this, deNOx process over Cu-ZSM-5/cordierite is also discussed.