Evaluation of Supplier Catalyst Formulations for the Selective Catalytic Reduction of NOx With Ammonia

The selective catalytic reduction of NO using urea (urea-SCR) is one of the promising technologies for removing NO_x from diesel engine exhaust. The engine-out NO_x is reduced by ammonia (NH₃) derived from urea over a catalyst to environmentally benign N₂. In this paper, we investigate the effect of various reactor operating conditions on the NO_x reduction performance of three different catalyst formulations (e.g., Cu-zeolite, Fe-zeolite, Vanadium-based) to obtain useful guidance in the design and operation of urea-SCR lean NO_x emission control systems. We examine the effects of NO:NO₂ ratio on the steady-state NO_x reduction activity at typical diesel engine exhaust temperatures (150-550°C). Transient measurements were also performed to determine the impact of NH₃:NO_x ratio and NH₃ storage on catalyst performance. The impacts of hydrocarbon poisoning and sulfur poisoning/regeneration were also examined.