Single and multisite detailed kinetic models for the adsorption and desorption of NO2 over Cu based NH3-SCR catalyst

Abstract

Kinetic modeling of NH3 Selective Catalytic Reduction (NH3-SCR) of NOx in Cu-chabazite washcoated monolithic reactors has recently become an important task for design, control and calibration of heavy-duty engine aftertreatment systems. Development of detailed and accurate kinetic models rely on the correct simulation of the NO₂ and NH₃ storage at different conditions. Here, different kinetic schemes for NO₂ adsorption and desorption were developed and compared to experimental data. For this purpose, firstly, realistic values of the active Cu sites in the Cu-zeolite were obtained using the temperature programmed desorption (TPD) of NH₃ and NO₂ which showed fractional coverages of 0.04 and 0.17 for the so-called ZCuOH and Z₂Cu species which reside in the 8 and 6 membered rings (MR) of the zeolitic framework, respectively. Active site concentrations were used in the kinetic models which included simultaneous formation of nitrate/nitrite species or the formation of HNO3 intermediate which in turn resulted in the formation of nitrates or nitrites over the ZCuOH. Models also included or excluded the NO₂ storage over the so called secondary Z₂Cu sites. It was shown that models taking into account HNO3 intermediate formation along with two NO₂ storage sites were better fits to the experimental data. 

Keywords

• NO2 Storage
• NH3 storage
• Kinetic model
• TPD
• NH3-SCR

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