12 research outputs found
Study of NH3-Standard SCR reactions over a commercial catalyst on powder and mini-SCRF forms
SSCI-VIDE+CARE+SML:AGFInternational audienceNon
Study of NH3-Standard SCR reactions over a commercial catalyst on powder and mini-SCRF forms
SSCI-VIDE+CARE+SML:AGFInternational audienceNon
Sulfur Deactivation of NOx Storage Catalysts: A Multiscale Modeling Approach
Lean NOx Trap (LNT) catalysts, a promising solution for
reducing the noxious nitrogen oxide emissions from the lean burn and Diesel engines, are
technologically limited by the presence of sulfur in the exhaust gas stream. Sulfur
stemming from both fuels and lubricating oils is oxidized during the combustion event and
mainly exists as SOx (SO2 and SO3) in
the exhaust. Sulfur oxides interact strongly with the NOx
trapping material of a LNT to form thermodynamically favored sulfate species, consequently
leading to the blockage of NOx sorption sites and altering the
catalyst operation. Molecular and kinetic modeling represent a valuable tool for
predicting system behavior and evaluating catalytic performances. The present paper
demonstrates how fundamental ab initio calculations can be used as a valuable source for
designing kinetic models developed in the IFP Exhaust library, intended for vehicle
simulations. The concrete example we chose to illustrate our approach was SO3
adsorption on the model NOx storage material, BaO.
SO3 adsorption was described for various sites (terraces, surface steps and
kinks and bulk) for a closer description of a real storage material. Additional rate and
sensitivity analyses provided a deeper understanding of the poisoning phenomena
Copper Coordination to Water and Ammonia in Cu II -Exchanged SSZ-13: Atomistic Insights from DFT Calculations and in Situ XAS Experiments
International audienceIn this study, the coordination sphere of copper in Cu–SSZ-13 as a catalyst for the selective catalytic reduction of NOx by ammonia is analyzed as a function of environmental parameters: temperature, partial pressure of water P(H2O), and partial pressure of ammonia P(NH3). By periodic density functional theory calculations, we obtain stability domains for variable loadings of water and ammonia (nH2O + mNH3 with (m + n ≤ 6)) close to CuII ions, which are located at 6-membered ring (6MR) or 8-membered ring (8MR) of the zeolitic structure. Ab initio calculations and thermodynamic investigations were performed to build phase diagrams, with vibrational analysis, so as to provide Gibbs free energy, G, values. Copper located in the 8MR appears to be more reactive toward H2O and NH3 adsorption than the one in the 6MR because of a lower coordination number of copper at 8MR in the absence of adsorbates. Depending on the operating conditions, structures containing adsorbed water and ammonia as ligands at the metal site can simultaneously be stabilized. The most widespread coordination number of CuII is 4 even at m + n > 4. The theoretical predictions were validated by in situ X-ray absorption spectroscopy, in dehydration conditions and in two gas atmospheres: dry He with P(NH3) = 10–3 bar (1000 ppm) and He with P(NH3) = 10–3 bar and P(H2O) = 10–2 bar. Trends in terms of ammonia desorption temperature as well as coordination numbers are well reproduced. Experimentally determined behaviors of CuI and CuII open new perspectives for the systematic computational investigation of the behavior of CuI in a H2O/NH3 atmosphere