In Situ X-ray Photoelectron Spectroscopy of Catalytic Ammonia Oxidation over a Pt(533) Surface

The NH3 + O-2 reaction on a Pt(533) surface has been studied in the 10(-4) mbar range and close to 1 mbar pressure with in situ X-ray photoelectron spectroscopy using synchrotron radiation. The coverages of the various O- and N-containing surface species have been followed in T-cycling experiments with varying mixing ratios O-2/NH3 and varying total pressure. In heating/cooling cycles hysteresis of similar to 50-100 K width occur. Adsorbed NOad already decomposes at T > 350 K. Under stationary conditions, no adsorbed NO could be detected. At no time during the experiments were Pt bulk oxides formed. A shift in the surface core level component of the Pt 4f spectrum by more than 0.5 eV toward higher binding energy is attributed to Pt atoms of the (100) step edges which are coordinated to more than one oxygen atom similar to the model proposed by Wang et al.