NO decomposition and reduction by CH4 over Sr/La2O3

Both NO decomposition and NO reduction by CH4 over 4%Sr/La2O3 in the absence and presence of O-2 were examined between 773 and 973 K, and N2O decomposition was also studied. The presence of CH, greatly increased the conversion of NO to N-2 and this activity was further enhanced by co-fed O-2. For example, at 773 K and 15 Torr NO the specific activities of NO decomposition, reduction by CH4 in the absence of O-2, and reduction with 1% O-2 in the feed were 8.3 . 10(-4), 4.6 . 10(-3), and 1.3 . 10(-2) mu mol N-2/s m(2), respectively. This oxygen-enhanced activity for NO reduction is attributed to the formation of methyl (and/or methylene) species on the oxide surface. NO decomposition on this catalyst occurred with an activation energy of 28 kcal/mol and the reaction order at 923 K with respect to NO was 1.1. The rate of N-2 formation by decomposition was inhibited by O-2 in the feed even though the reaction order in NO remained the same. The rate of NO reduction by CH4 continuously increased with temperature to 973 K with no bend-over in either the absence or the presence of O-2 with equal activation energies of 26 kcal/mol. The addition of O-2 increased the reaction order in CH4 at 923 K from 0.19 to 0.87, while it decreased the reaction order in NO from 0.73 to 0.55. The reaction order in O-2 was 0.26 up to 0.5% O-2 during which time the CH4 concentration was not decreased significantly. N2O decomposition occurs rapidly on this catalyst with a specific activity of 1.6 . 10(-4) mu mol N-2/s m(2) at 623 K and 1220 ppm N2O and an activation energy of 24 kcal/mol. The addition of CH4 inhibits this decomposition reaction. Finally, the use of either CO or H-2 as the reductant (no O-2) produced specific activities at 773 K that were almost 5 times greater than that with CH4 and gave activation energies of 21-26 kcal/mol, thus demonstrating the potential of using CO/H-2 to reduce NO to N-2 over these REO catalysts.