Inhibition of NH<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si161.svg" display="inline" id="d1e428"><mml:msub><mml:mrow/><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:math>-SCR over Cu-CHA at high partial pressures of water: Measurements and DFT-based kinetic modeling
Shivangi Singh, Yingxin Feng, Ton V. W. Janssens, Henrik Grönbeck
Abstract
Cu-exchanged chabazite (Cu-CHA) is a widely applied catalyst for selective catalytic reduction of nitrogen oxides in oxygen excess. The application of Cu-CHA to exhaust from H 2 -fueled engines depends on the behavior of this material at high partial pressures of water. We have performed flow-reactor measurements, which show that the NO x conversion at 200 °C over a Cu-CHA (3.2 wt% Cu, Si/Al=6.7) catalyst decreases with increasing partial pressures of water from 2 to 25%. Simultaneously, the apparent reaction order in water decreases from − 0 . 17 to − 1 . 18 , following the simple empirical equation − 3 . 43 ( p H 2 O / p ∘ ) 0 . 76 . The experimental results are corroborated with DFT-based microkinetic modeling. The DFT calculations show that H 2 O competes with NO adsorption on the Cu-sites and hinders the reaction. The kinetic model describes accurately the inhibiting effect of water after minor adjustments to the computed Gibbs free energies of water adsorption.