Improvements in the N2 selectivity of Pt catalysts in the NO–H2–O2 reaction at low temperatures

The selective reduction of NO with H2 in the presence of excess O2 (the NO–H2–O2 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% H2. Pd, Ir, and Rh catalysts were also highly active in the presence of 1% H2. 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 N2 by the selective reduction of NO with NH3 over H-ZSM-5, which was physically mixed with the Pt catalyst.