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 NO_x 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 NO_x reduction, NH₄NO₃ formation and decomposition pathways was proposed in this paper, and the influence of NH₄NO₃ on the NO_x reduction pathways and low-temperature catalytic activity was studied using the described model. As an important intermediate product of NO_x 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.