Reaction mechanism and chemical kinetics of NH 3 -NO/NO 2 -SCR system with vanadium-based catalyst under marine diesel exhaust conditions

As one of the most effective NOx emission removing technologies to meet the Tier III limitation by International Maritime Organization, urea-selective catalytic reduction (SCR) technology is starting to be used in two-stroke marine diesel engines. Based on the two-cycle catalytic mechanism proposed by Topsoe, in combination with the exhaust characteristics of the marine diesel, expansion studies on detailed SCR reaction model were carried out in this paper. According to the temperature dependence of reaction pathway, SCR reaction model was divided into three parts: low temperature reaction pathway, standard SCR reaction pathway, and high temperature oxidation pathways, and an expanded NH₃-NO/NO₂-SCR reaction model for V₂O₅ catalyst was proposed in the paper. In order to verify the accuracy of the expanded SCR reaction model, simulating and testing studies of SCR reaction under marine diesel conditions were carried out with a commercial extruded V₂O₅/TiO₂ catalyst. The simulation values are agreed well with experimental values at 150–500 ℃, and kinetics characteristics of SCR reaction process under V₂O₅/TiO₂ catalyst can be predicted accurately with the expanded NH₃-NO/NO₂-SCR reaction model.