Browse Publications Technical Papers 2019-24-0150
2019-09-09

Analysis and Modeling of NOx Reduction Based on the Reactivity of Cu Active Sites and Brønsted Acid Sites in a Cu-Chabazite SCR Catalyst 2019-24-0150

In this study, the NOx purification reactivity of a Cu-chabazite SCR catalyst was analyzed over a wide temperature range based on the NH3-SCR mechanism considering Cu redox reactions and reactions on a Brønsted acid site. It was revealed that the De-NOx reactions on the active site of Cu proceeded in different paths at lower and higher temperatures. This means that the rate-limiting step of SCR reactions was changed as each temperature. The reaction rate of NOx purification on a Cu site less than 200 °C was determined by the reaction rate of oxidation of Cu sites. On the other hand, the NH3 adsorption on Cu sites played a dominant role in NOx purification at temperature range higher than 300°C. Moreover, it was also observed that the Cu reaction site took different states at low and high temperatures during the NOx purification and was estimated that the valence state of a Cu site was changed as the temperature increased. In order to analyze the reaction on a Brønsted acid site of chabazite structure, analysis using an H-chabazite catalyst was also carried out. It was observed that NOx purification by NO2 -NH3 reaction took place on a Brønsted acid site. NH3 oxidation which had significant impact on the DeNOx reactivity in the high temperature region, did not occur on a Brønsted acid site. Numerical studies were also carried out to develop a SCR reaction model considering the effects mentioned earlier. As a results, we showed this model can describe the NOx purification phenomena where the temperature changes transiently.

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