Selective oxidation of ammonia over Ir(5 1 0). Comparison with Ir(1 1 0)

The decomposition and oxidation of NH3 have been studied on the Ir(5 1 0) surface in the temperature range from 300 K up to 800 K. Decomposition of NH3 at room temperature and combination of N-atoms to form N2 was observed. The products of ammonia oxidation were N2 and H2O. NO and N2O were not observed. Inhibition of the reaction by N species seems to exist until a certain temperature (between 400 and 500 K, depending on the NH3/O2 ratio). Above those temperatures the reaction starts as manifested by a decrease in NH3 and O2 pressures and a simultaneous increase in H2O and N2 pressures. Reaction orders with respect to NH3 and O2 were found to have values between 0.5 and 0.7. A comparison with previous results obtained on the Ir(1 1 0) surface is made.