Catalytic Reactions of NO over 0–7 mol% Ba/MgO Catalysts: I. The Direct Decomposition of NO

A series of catalysts composed of barium oxide supported on magnesium oxide with Ba loadings up to 7 mol% has been studied for NO and N2O decomposition. Nitrous oxide is an intermediate in the decomposition of nitric oxide; however, the rate of N2O decomposition is much greater than that of NO decomposition so that the selectivity for N2 formation approaches 100% at T>700°C. Over 4 mol% Ba/MgO catalyst, the rate of N2 formation at 800°C was 0.22 μmol g−1 s−1 for a gas stream containing 1% NO in He. When the inhibiting effect of O2 is properly accounted for, the reaction order with respect to NO is two. This order is consistent with a mechanism in which gas-phase NO reacts with a surface NOx species that is probably present in an ionic form, considering the temperatures at which the reaction occurs. In situ Raman spectroscopy has demonstrated the presence of nitrate and nitrite ions on the surface, but the exact nature of the surface intermediate is not known.