Selective oxidation of ammonia over Ir( [formula omitted]). Comparison with Ir( [formula omitted

Abstract

The decomposition and oxidation of NH 3 have been studied on the Ir(5 1 0) surface in the temperature range from 300 K up to 800 K. Decomposition of NH 3 at room temperature and combination of N-atoms to form N 2 was observed. The products of ammonia oxidation were N 2 and H 2O. NO and N 2O 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 NH 3/O 2 ratio). Above those temperatures the reaction starts as manifested by a decrease in NH 3 and O 2 pressures and a simultaneous increase in H 2O and N 2 pressures. Reaction orders with respect to NH 3 and O 2 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.