The selective reduction of NO with H-2 in the presence of excess O-2 (the NO-H-2-O-2 reaction) over noble metal catalysts, with a particular emphasis on the use of Pt, was investigated. The conversion of NOx exceeded 98% with Pt catalysts at between 350 and 500 K in the presence of 1% H-2. Pd, Ir, and Rh catalysts were also highly active in the presence of 1% H-2. NH3 was formed as a byproduct over Pt catalysts between 350 and 400 K. The formation of NH3 increased over Pt supported on ZrO2. The NH3 formed at around 400 K was effectively converted to N-2 by the selective reduction of NO with NH3 over H-ZSM-5, which was physically mixed with the Pt catalyst. (C) 2003 Elsevier B.V. All rights reserved.