Kinetics of ammonia oxidation on stepped platinum surfaces

A mean field model is presented describing the kinetics of ammonia oxidation with oxygen on two stepped Pt(1 1 1) surfaces, Pt(5 3 3) and Pt(4 4 3), under low pressure conditions (p < 10−3 mbar). It is shown that the experimental data of both surfaces can be simulated with good agreement with a strongly simplified mechanism which neglects NHx (x = 1, 2) intermediates and contains direct H abstraction from NH3 by adsorbed oxygen as essential step. The model works quantitatively in excess of oxygen, but with ammonia being in excess the agreement worsens.