LNT Morphology Changes with Lean/Rich Cycling
Charles Peden, Pacific Northwest National Laboratory
The fundamentals of NOx uptake/release processes have been studied extensively on NOx storage/reduction (NSR) catalysts (also known as lean-NOx traps (LNTs) and NOx adsorber catalysts) based on BaO on alumina support. The formation of different NOx species on the active BaO phase has clearly been shown, however, their identity has not been unambiguously determined. In order to understand the processes that take place upon NOx adsorption on these BaO/Al2O3 catalysts in different reactant gas mixtures, and in the subsequent regeneration, we have undertaken studies utilizing a series of spectroscopic techniques. The adsorption of NOx was investigated on 2%, 8%, and 20% BaO/Al2O3 catalysts with or without Pt using a series of in situ spectroscopic techniques: FTIR, TPD, 15N and 27Al MAS NMR, and synchrotron TP-XRD. TEM has also been used to follow morphological changes during NOx adsorption and desorption processes. The results of these investigations allowed us to propose a morphology cycle that the BaO/Al2O3 systems go through during NOx uptake and release. We utilize these same methods to also study the effects of high temperature processes on the morphologies and performance of these model LNT catalysts.