Study of the remarkable reactivity of HNCO/urea with NO2 in the NOx SCR by urea process over an oxide-based catalyst

Abstract

An exceptional reactivity between NO₂ and probably HNCO was demonstrated over an oxide-based catalyst during NO₂-SCR experiments with urea as the injected reductant. This was observed when only NO₂ was used as NO_x, but not with gaseous NH₃ as the reductant. Roughly, one third of the injected reductant reacted with NO₂ and two thirds appeared to be oxidized by O₂, the main product being N₂. 28 reactions may be involved in the observed results. A cooperative effect of NO₂ with O₂ was demonstrated and the observed global stoichiometry did not depend on the NO₂ concentration for (NO₂/eq. NH₃)_{inlet ratio} ≤1.