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 ad sorbates during the selective oxidation of ammonia to N-2 at potential s where platinum is free of oxides. These adsorbates are inactive in t he formation of N-2 and consist of NHx, probably N-ads, 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 N-2 and NH3 a re formed. When this potential scan is interrupted by holding the pote ntial at 0.55 V the current reverses from negative to positive, being accompanied by N-2 formation. These data support a mechanism in which NHx species, proposedly NHads, are the active intermediates and N-ads acts as a poison. (C) 1998 Elsevier Science Ltd. All rights reserved.