Catalysts for lean NOx reduction: structure-property relationship

Effective reduction of NOx to N-2 using hydrocarbon in the presence of a high concentration of O-2 can be accomplished using Al2O3-supported Co, Ag, or Au catalysts. However, the maximum NO conversion to N-2 is higher on catalysts of lower metal loadings in the case of Co and Ag, which is due to the fact that the metal ions in these catalysts are more dispersed and more difficult to undergo redox than ions in catalysts of higher metal loadings. In the case of Au/Al2O3, the maximum NO conversion to N-2 depends on the crystallite size of Au. The effect of the presence of NO on the hydrocarbon oxidation reaction depends on the combustion activity of the catalysts: NO suppresses hydrocarbon combustion on more active combustion catalysts but facilitates it on less active ones. (C) 1997 Elsevier Science B.V.