Influence of NH4NO3 Formation on the NOx Reduction Pathways over Vanadium-based Catalyst under Diesel Exhaust Conditions

Abstract

Nitrates are often deposited on the pipe wall and catalyst surface in the SCR system, so the NOx removing efficiency and catalytic activity are also reduced and limited at low exhaust temperatures. According to working characteristics and exhaust conditions of Diesel engine, a NH3−NO/NO2−SCR reaction model including NOx reduction, NH4NO3 formation and decomposition pathways was proposed in this paper, and the influence of NH4NO3 on the NOx reduction pathways and low-temperature catalytic activity was studied using the described model. As an important intermediate product of NOx reduction at low temperatures, NH4NO3 formation rate is strongly dependent on the apparent rate of SCR reaction. Since NH4NO3 formation reaction is enhanced in the presence of H2O, and its decomposition is controlled by the exhaust temperature, both reactions can proceed into a quasi-equilibrium state at high temperatures.