Catalytic Reduction of Nitrogen Oxides by Methane over Pd(110)

The catalytic reduction of NO with CH4 has been studied over Pd(110) in the temperature range 700−800 K at a total pressure of 10 Torr. The rate of NO reduction is at a maximum at a high CH4/NO stoichiometry (8/1) and at a minimum at a low (1/4) CH4/NO ratio. Correspondingly, the activation energy for NO reduction decreases with increasing CH4/NO ratio, and the reaction orders are −1.0 in NO and +1.5 in CH4. Unlike NO, the rate of N2O reduction is at a maximum at low CH4 pressures, and the reaction orders are positive in N2O and negative in CH4. In the presence of oxygen, NO is oxidized to NO2, which is in turn reduced back to NO by CH4. The NO/NO2 oxidation/reduction cycle has the effect of delaying NO reduction to N2 (or N2O) until all of the O2 is consumed.