Kinetic Modeling Study of NOx conversion based on Physicochemical Characteristics of SCR/DPF Catalyst with Hydrothermal Aging

Paper #:
  • 2017-01-2386

  • 2017-10-08
Diesel engines have better fuel economy over comparable gasoline engines and useful for the reduction of CO2 emissions. However, to meet stringent emission standards, the technology for reducing NOx and particulate matter (PM) in diesel engine exhaust needs to be improved. A conventional selective catalytic reduction (SCR) system consists of a diesel oxidation catalyst (DOC), a diesel particulate filter (DPF), and an urea-SCR catalyst. Recently, more stringent regulations have led to the development of SCR systems with a larger volume and increased the cost of such systems. In order to solve these problems, an SCR catalyst coated on DPF (SCR/DPF) is proposed. An SCR/DPF system has a lower volume and cost compared with the conventional SCR system. The SCR/DPF catalyst has two functions: one is combustion of PM and the other is reduction of NOx emissions. As PM is removed from the DPF at high temperatures (> 650°C), the SCR/DPF system is exposed to higher temperatures compared with the conventional SCR system. In this study, we investigated the NOx reduction performance and the properties of hydrothermal-aged SCR/DPF catalyst. Using these data, a model, which can predict the NOx conversion of the hydrothermal-aged SCR/DPF catalyst, was constructed. A commercial copper-exchanged zeolite catalyst, Cu-ZSM-5, was used and aged using synthetic air with 10% of water at a temperature range of 650-750 °C. The effects of hydrothermal aging on the catalysts were investigated using a synthetic gas bench, and a detailed analysis of the structure of the hydrothermal-aged catalyst was performed. Using the experimental data, we succeeded in constructing a hydrothermal-aged SCR/DPF model for the prediction of NOx conversion based on changes in the physicochemical characteristics of the catalysts with a change in hydrothermal aging conditions. This work is the first step toward bridging the gap between lab-simulate performance model and global reactivity observed under real world conditions.
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