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 (similar or equal to 150 degreesC). The formation of MnOx-CeO2 solid solutions with the fluorite-type structure at n similar or equal to 0.5 was found to be quite effective in accelerating NOx sorption from flowing mixtures of 0.08% NO, 2% O-2, and He balance (W/F = 0.24 g.s/cm(3)). The cumulative NOx uptake was increased by decreasing the reaction temperature and/or by increasing O-2 concentration, indicative of chemisorption via oxidation of NO/NO2. In situ FT-IR diffuse reflectance spectrometry demonstrated that adsorption of NOx as bidentate, monodentate, and ionic nitrates is responsible for the large uptake. These adsorbates are produced by oxidative adsorption, which is caused by NO oxidation to NO2 by lattice oxygens bound to Mn and subsequent coordination to Ce in adjacent surface sites. XPS and O-2-TPD studies suggested that the active site for NO oxidation should be related to the redox of Mn and accompanying reversible sorption/desorption of lattice oxygens.