Comparative NOx reduction behavior of Pt, Pd, and Rh supported catalysts in simulated exhaust gases as a function of oxygen concentration

NO x reduction activity on Pt and Pd catalysts had a maximum for S value as stoichiometry number at a fixed temperature, and the S value at the maximum NO x conversion increased with decreasing temperature. NO x conversion on Rh catalyst increased with decreasing S value, but independent of temperature. As for the effect of HC on NO x reduction behavior, it was concluded that, for Pt and Pd catalysts, HC adsorbs strongly on the catalysts surface to cause the self-inhibition. Increasing O2 concentration lead to oxidation of HC, but decreased the value of NO/O2 ratio. The balance point of the two factors generated a maximum NO x conversion. For Rh catalyst, the strongly adsorbed oxygen is more reactive with decreasing S value, and thus NO x conversion is increased.