Two challenging reactions, the oxy-dehydrogenation of NH3 and the reduction of N2O, were investigated on model metallic surfaces, combining characterisation of model surfaces under low pressures of reactants and kinetics measurements.
New insights into the reactions mechanisms were in particular brought by the in situ determination of the surface intermediates by FT-RAIRS. XPS was also used to characterise the catalyst surface at various extents of conversion. The influence of oxygen upon the two reactions was addressed.
On Cu(110), at 600K, in the presence of an NH3+O2 equimolecular mixture, the active catalyst surface is a mixed oxy-nitride layer. On that new surface phase, the reaction proceeds via a progressive dehydrogenation of ammonia by adsorbed oxygen. The formation of NH2, NH and of a polarised dinitrogen species, adsorbed on Cu(110), was evidenced. An excess of oxygen, or a higher reaction temperature, leads to the formation of N2O, an undesired product of the reaction.
- At temperature below 750 K, N2O dissociation leads to the formation of an oxide surface layer that rapidly blocks the reaction.
- At temperature above 750 K, N2O can be reduced by a NH3 + O2 mixture.
In situ RAIRS characterisation of the copper surface again made clear the formation of NH2, NH and a N2d- adsorbed species. The IR frequency of it’s stretch mode is strongly influenced by the atomic environment of this species making this molecule a probe to assess the surface occupancy by oxygen or hydroxyls.
A surface science approach, combined with kinetics tests enables us to suggest that the reactivity of N2O is strongly related to the concentration of oxygen on the surface.

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