High performance NH₃ SCR zeolite catalysts for treatment of NO_x in emissions from off-road diesel engine

The leading approach for reduction of NO_x from diesel engines is selective catalytic reduction employing urea as a reductant (NH₃ - or urea-SCR). For passenger vehicles, the best known NH₃ -SCR catalysts are Cu-ZSM-5 and Fe-ZSM-5 and have been shown to function very well in a narrow temperature range. This technology is not directly transferable to off-road diesel engines which operate under a different duty cycle resulting in exhaust with different fractions of components than are present in passenger vehicle emissions. Our results show that Cu-ZSM-5 exhibits 90% NO_x reduction efficiency in 250-450°C range while Fe-ZSM-5 is highly effective in 350-550°C range for off-road engines. However, a combination of these catalysts cannot efficiently reduce NO_x in 150-650°C which is the desirable range for deployment in off-road diesel engines. In our efforts to increase the effective range of these catalysts, we initiated efforts to modify these catalysts by catalyst promoters. In this paper, we describe our results on synthesis, characterization, and testing of new zeolites prepared by selective partial replacement of framework aluminum with trivalent ions. The new hetero-bimetallic MFI-zeolite, formed by partial replacement of framework aluminum with indium, exhibits high NO_x conversion performance at 150°C. The impact of aging on the NO_x reduction efficiencies of these catalysts is also presented.