Modelling and parametric investigation of NO_x reduction by oxidation precatalyst-assisted ammonia-selective catalytic reduction

Nitrogen oxide (NO_x) reduction by the selective catalytic reduction (SCR) system assisted by an oxidation precatalyst is modelled and analytically investigated. The Langmuir- Hinshelwood SCR kinetic scheme with vanadium-based catalyst and ammonia (NH₃) reductant in conjunction with the NO-NO₂ conversion reaction over a platinum-based catalyst is used. The effects of the ratio of the oxidation precatalyst to the SCR monolith volume, the gas temperature, the space velocity, and the NH₃-to- NO_x concentration ratio on the de-NO_x performance are parametrically examined. The oxidation precatalyst promotes NO_x conversion at low temperatures. At intermediate temperatures, the NO_x reduction is either activated or deactivated with increase in the space velocity. A higher oxidation precatalyst-to-SCR monolith volume ratio tends to promote the NO_x reduction of higher space velocities. At high temperatures, the de-NO_x efficiency is very high and insensitive to the space velocity. The NO_x conversion efficiency depends on the NH₃-to-NO_x ratio at low temperatures.