THE NITRIC-OXIDE AMMONIA RECTANGULAR PULS E TECHNIQUE (NARP) - EVALUATION OF A METHOD FOR THE TITRATION OF TERMINAL OXYGEN SPECIES ON METAL-CATALYSTS

The NARP-(Nitric-Oxide Ammonia Rectangular-Pulse) technique is often u sed as a method for the quantitative determination of the number of te rminal Me=O oxygen species in metal oxide catalysts. The amount of nit rogen formed when pulsing NO/NH3-mixtures over the catalysts are relat ed to the surface density of Me=O groups. In the present paper the app licability of this method, which is not generally accepted in literatu re, was tested for unsupported and supported vanadia- and molybdena ca talysts. The influence of the reaction temperature and calcination tem perature of the catalysts applied on the nitrogen formation do not sup port the applicability of this method for a quantitative determination of the number of terminal Me=O oxygen species on metal oxide surfaces . However, the comparison of NARP results and XPS surface analyses pre sume, that the NARP technique can be used to determine the surface cov erage of VOx and MoOx species on supported V-(Mo-)catalysts.