Modeling of kinetic expressions for the reduction of NOx by hydrogen in oxygen-rich exhausts using a gradient-free loop reactor

The reduction of NOx by hydrogen under lean conditions is investigated in a gradient-free loop reactor. Using this computer-controlled reactor, the reaction rates can be measured under exact isothermal conditions. Systematic variation of the input concentrations of hydrogen, nitric oxide, oxygen as well as reaction temperature provides a complete data set of reaction rates for the given reaction system. A number of kinetic rate expressions were evaluated for their ability to fit the experimental data by using toolboxes of MATLAB. The temperature influence on reaction rate constants and adsorption equilibrium constants were correlated simultaneously using Arrhenius and van't Hoff equations, respectively. The kinetic rate expression based on a Langmuir-Hinshelwood-type model describes the data and the model can be improved by introducing a correction term in square root of hydrogen partial pressure over the range of conditions investigated.