A DEMS and cyclic voltammetry study of NH3 oxidation on platinized platinum

The oxidation of ammonia on platinized platinum has been studied with cyclic voltammetry and differential electrochemical mass spectrometry (DEMS). These techniques show the surface to be highly covered with adsorbates during the selective oxidation of ammonia to N2 at potentials where platinum is free of oxides. These adsorbates are inactive in the formation of N2 and consist of NHx, probably Nads, whereas no NO adsorbates are present among these adspecies. These adsorbates remain present on the surface after exchange of the ammonia solution for base electrolyte and in a negatively directed potential scan N2 and NH3 are formed. When this potential scan is interrupted by holding the potential at 0.55 V the current reverses from negative to positive, being accompanied by N2 formation. These data support a mechanism in which NHx species, proposedly NHads, are the active intermediates and Nads acts as a poison.