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.