MnO<i>_x</i>−CeO₂ Binary Oxides for Catalytic NO<i>_x</i>-Sorption at Low Temperatures. Selective Reduction of Sorbed NO<i>_x</i>

Abstract

The reactivity of NO x sorbed onto MnO x −CeO 2 toward H 2 was studied in the presence of impregnated Pd catalyst by use of TPR, H 2 pulse reactions, in situ FT-IR, and steady-state NO−H 2 −O 2 reactions. The Pd-loaded catalyst after saturated NO x -sorption at 150 °C could be regenerated by micropulse injections of H 2, which ensure the reduction of monodentate, bidentate, and ionic nitrates sorbed on MnO x −CeO 2 into N 2 . In the steady-state NO−H 2 −O 2 reaction, gaseous NO x was first sorbed onto MnO x −CeO 2 and subsequently reduced at the PdO/MnO x −CeO 2 boundary. Despite the nonselective character of Pd catalysts toward NO x −H 2 reaction, Pd/MnO x −CeO 2 attained 65% NO-conversion of a stream of 0.08 vol % NO, 2 vol % H 2, and 6 vol % O 2 in He at a low temperature of 150 °C, compared to ∼30% for Pd/γ-Al 2 O 3, the reaction on which was more suppressed by the competitive H 2 −O 2 reaction. The combination of NO x sorbability of MnO x −CeO 2 and H 2 activation of Pd catalysts was found to give rise to a synergistic effect, thus paving the way to development of NO x -sorbing catalysts for selective deNO x processes at low temperatures (<150 °C).