Characterization of the chemical mechanisms of automotive catalysts

The automotive catalyst allows for treating exhaust gases and eliminating pollutants. A sound understanding of the chemistry involved is necessary in order to improve catalysts and thus meet anti-pollution standards, notably concerning diesel and lean-running engines. The selective reduction of nitrogen oxides by alumina-supported silver is one of the most promising processes. In the laboratory, infrared spectroscopy can detect the chemical species that appear on the catalyst during operation (operando mode) in order to monitor surface reactions and determine the chemical mechanism at work. The evolution of species on the surface is correlated to changes in the concentration of gases at the reactor outlet and the kinetic profiles of the reaction can be detected by sending pulses of reactants on the catalyst. The fastest stages can be detected via step-scan spectroscopy (with a maximum resolution of a few nanoseconds) by using a femtosecond pulsed laser in order to trigger the catalytic reaction.