MnOx-CeO2 binary oxides for catalytic NOx sorption at low temperatures. Sorptive removal of NOx

Interactions of nitrogen oxides (NOx) with (n)MnOx-(1-n)CeO2 binary oxides were studied to use them for sorptive NO, removal at low temperatures (simi lar or equal to 150 degreesC). The formation of MnOx-CeO2 solid solutions w ith the fluorite-type structure at n similar or equal to 0.5 was found to b e quite effective in accelerating NOx sorption from flowing mixtures of 0.0 8% NO, 2% O-2, and He balance (W/F = 0.24 g.s/cm(3)). The cumulative NOx up take was increased by decreasing the reaction temperature and/or by increas ing O-2 concentration, indicative of chemisorption via oxidation of NO/NO2. In situ FT-IR diffuse reflectance spectrometry demonstrated that adsorptio n of NOx as bidentate, monodentate, and ionic nitrates is responsible for t he large uptake. These adsorbates are produced by oxidative adsorption, whi ch is caused by NO oxidation to NO2 by lattice oxygens bound to Mn and subs equent coordination to Ce in adjacent surface sites. XPS and O-2-TPD studie s suggested that the active site for NO oxidation should be related to the redox of Mn and accompanying reversible sorption/desorption of lattice oxyg ens.