The relation between surface state and reactivity in the DeNO(x) mechanismon platinum-based catalysts

The selective reduction of nitrogen oxides by hydrocarbon on Pt supported o n La2O3, ZrO2, and a mixture of both has been studied. The supports were pr epared by a sol-gel technique. Following a standard pretreatment with oxyge n and water, it was found that the platinum was existing in a mixture of bo th oxidised and reduced forms, yet during the course of the reduction react ion, all of the metal became oxidised. A systematic study of the parameters influencing the reaction demonstrated NO2 is not a reaction intermediate. The metal remains fully oxidised during the course of the reaction and the hydrocarbon is unable to reduce it; therefore the SCR proceeds without NO d issociation. (C) 1999 Academic Press.