Deactivation Reactions on a Commercial Lean NOx-trap - Effect of Hydrocarbon Nature, Concentration and Operation Temperature

Abstract Engine-out emissions during rich phase operation of a lean NOX trap (LNT) catalyst contain a mixture of different hydrocarbons (HCs) depending on engine operation and fuel type. The impact of temperature, as well as type and concentration of HC on reactions and deactivation potential on a commercial LNT catalyst was analyzed by lean-rich cycle measurements and subsequent temperature programmed oxidation. Deactivation during the rich phase is omitted initially by O species adsorbed or stored by CeO2, but formation of amorphous carbon and significant deactivation of noble metal sites occur in the presence of C2H2. Carbon formation and deactivation of Pt sites correlate with the reforming reaction of C2H2, thus emphasizing the significance of this reaction in the rapid build-up of carbonaceous deposits. Coking and deactivation decreases with decreasing C2H2 concentration and reaction temperature that determine the extent of reforming reaction. DFT calculations of adsorption energies on sites of Pt (111) or Pt10/CeO2 verify that abundance of HCs on the Pt surface, relative to other feed components, determines which reactions occur and thus the coking degree. This aligns with the finding that HCs with lower adsorption energy, such as C2H4 or C3H6, are less reactive and significant catalyst deactivation is absent during their presence.