Lean NOx Catalyst Evaluation and Characterization

Copper ion exchange procedures were used to prepare zeolite-based catalysts for NO_x reduction in lean (oxygen-rich) exhaust. Energy dispersive x-ray fluorescence and scanning electron microscopy analyses confirmed the presence of copper in the zeolite matrix. Zeolites were applied onto honeycomb and foam substrates, and evaluated for catalytic NO_x reduction efficiency using engine exhaust. Copper-exchanged zeolite catalysts prepared for this study revealed NO_x reduction of 95 percent for a period of seven minutes using previously adsorbed exhaust hydrocarbons as the reducing agent. Experiments using ethylene injection to supplement the exhaust suggest long-term and sustained NO_x reduction, initially observed at 52 percent. Experimental results and performance comparisons of ZSM-5, mordenite, and Y-type zeolites are discussed. Zeolite catalysts based on Cu-mordenite showed high levels of initial NO_x reduction, while results using Cu-ZSM-5 suggested better long-term activity.