| Abstract
| - The reactivity of NOx-adsorbing material, MnOx−CeO2, toward H2 has been studied in the presence ofimpregnated Pd catalysts by the use of micropulse reactions, in situ DRIFT spectroscopy, and chemisorptionexperiments. It was found that NOx adsorbed on Pd/MnOx−CeO2 can be largely removed by micropulse H2injections at 150 °C, which ensure the conversion of nitrite adsorbates (NO2-) into N2 and thus recover theadsorbability. The results of O2−H2 titration evidenced that the role played by Pd is to produce atomic hydrogen,which spills over onto MnOx−CeO2 and leads to the reduction of the surface. The amount of spilt-over hydrogenwas strongly dependent on temperature and the composition of MnOx−CeO2; the equimolar oxide (0.5MnOx−0.5CeO2) exhibited ca. 270-fold larger hydrogen uptake compared to the number of surface Pd atom(nH/nPds = 270) at 150 °C. The anion vacancies thus formed on MnOx−CeO2 could be refilled by oxygenspilt-over from Pd. When H2 was supplied after saturated by the oxidative NO adsorption at 150 °C, hydrogenspilt-over from Pd caused not only the reduction of nitrite species adsorbed on MnOx−CeO2, but also thereaction between the anion vacancy and gaseous NO. Consequently, two types of spillover-assisted mechanismsfor NO−H2 reactions were proposed to explain the reason the reduction of adsorbed nitrite spreads out to thewhole surface of MnOx−CeO2.
|
