Nitrate Formation/Decomposition On Ba-, and K-Based Model LNT Catalysts: Similarities and Differences

Diesel engines are a promising near-term solution for obtaining high energy efficiency because of their unparalleled power density and low CO₂ emissions.  However, there are challenges for the catalytic aftertreatment systems, especially due to the necessity to selectively reduce nitrogen oxides (NO_x) in the net oxidizing environment.  NO_x storage-reduction (NSR) catalysts are generally considered as one of the potential options for removing NO_x in the diesel engine exhaust.  In the NSR technology, alkali or alkaline earth elements (K or Ba) take up NO_x under lean operation and store them as nitrates, which are subsequently reduced during rich operation.  In this presentation, we compare the characteristics of Ba and K storage elements during NOx adsorption and desorption processes using multiple techniques, including TR-XRD, FTIR and NO₂ TPD.  We find that, although both elements store NOx as nitrates, there are significant differences between the morphology changes of the Ba and K nitrates.