Study on metal-MFI/cordierite as promising catalysts for selective catalytic reduction of nitric oxide by propane in excess oxygen

Abstract

ZSM-5 and AlTS-1 zeolites were successfully in situ synthesized on the surface of honeycomb cordierite substrate, certified by XRD and SEM techniques. Strong interaction between zeolite and substrate developed during in situ synthesis, entailing improved hydrothermal stabilities of the zeolites. A series of nonnoble metal ion-exchanged ZSM-5/cordierite and AlTS-1/cordierite were studied as catalysts for the selective reduction of nitric oxide by propane under dry and wet conditions. In the deNO x processes, NO x (ads) and C x H y O z (ads) were thought as the important reaction intermediates and the formation of them on the catalysts was a key step in deNO x reactions. Based on this, the factors that influence the activities of the catalysts were discussed considering not only the active components but also the supports. As for the active components, the ability to adsorb gas reactants and the oxidative activity are two dominant factors that determined the deNO x activities. As for the supports, the Brønsted acidity and oxidative activity are two important factors that influenced the deNO x activities. From the catalytic testing results, Cu-ZSM-5/cordierite is selected as a promising SCR deNO x catalyst due to its superior deNO x activity and high selectivity. For practical purposes, the catalytic testing of Cu-ZSM-5/cordierite was also preformed on a real lean-burn engine. Hydrocarbons and carbon monoxide in the exhaust were directly used as reductants for NO x reduction. Thus, three main pollutants in the exhaust could be removed simultaneously. As expected, Cu-ZSM-5/cordierite also exhibited a rather good durability due to the in situ synthesis method.