Regeneration mechanism of Pt/BaO/Al2O3 lean NOx trap catalyst with H2

NOx Storage and Reduction for Diesel Engine Exhaust Aftertreatment

“…The reactants and product profiles shown in Fig. 7 are in agreement with mechanistic aspects of the regeneration already reported [45,81,83,84]. The reduction of stored nitrates with hydrogen has been found to occur by the following reactions:…”

“…This finding implies again that the supply of the reductant H2 is controlling the NSR process. This was also observed by Mulla et al [81] that measured the time required for regenerate the trap catalyst by the width of the N2 pulse in a mass spectrometer. Analogously, Nova et al [45] had also noticed that the N2 production during the regeneration of a PtBaO/Al2O3 catalyst was limited by the amount of H2 fed to the reactor.…”

“…On the other hand, the complete consumption of H2 during the initial period of the regeneration together with the rectangular shape of the H2O and N2 formation curve indicates a "plugflow" type of the regeneration mechanism. As several authors have already reported [45,78,81,82], the hydrogen front travels through the catalyst bed with complete regeneration of the trapping sites as it propagates down the bed with regeneration time.…”

“…11. Mulla et al [81] also reported the overall rate for NOx reduction as a linear function of rate of flow of H-atoms in the form of H2 or NH3 at 300 °C. Their observations also confirmed that the regeneration process was not mass transfer or kinetically limited, but it was controlled by the supply of the reductant H2.…”

Formation and removal of Ba-carbonates or carboxylates on Pt/BaO/γ-Al2O3 lean NOx traps

“…This allows the traps to oxidize much of the NO in the exhaust stream to NO 2 over Pt [4,5] and capture the NO x (NO and NO 2 ) in the form of nitrites and nitrates on the Ba storage component during the lean phase [6,7]. Then the rich phase regenerates the Ba by converting adsorbed NO x species into N 2 [8,9]. Thus over a pair of sufficiently long lean-rich phase exposure periods, a LNT has the capability of converting 100% of the harmful NO x emissions from the engine exhaust into N 2 .…”