Sulfur Deactivation of NOxStorage Catalysts: A Multiscale Modeling Approach

Abstract

Lean NO<sub><i>x<i/><sub/> 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 SO<sub><i>x<i/><sub/> (SO<sub>2<sub/> and SO<sub>3<sub/>) in the exhaust. Sulfur oxides interact strongly with the NO<sub><i>x<i/><sub/> trapping material of a LNT to form thermodynamically favored sulfate species, consequently leading to the blockage of NO<sub><i>x<i/><sub/> 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 <i>ab initio<i/> 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 SO<sub>3<sub/> adsorption on the model NO<sub><i>x<i/><sub/> storage material, BaO. SO<sub>3<sub/> 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.