A Comparative Study of Rh-only, Pd-only and Pd/Rh Catalysts

ABSTRACT With the increase in worldwide automobile usage and the tightening of associated emissions legislation, the total demand of PGMs for use in automotive emission control catalysts is growing. Reducing the amount of required PGM in automotive catalysts as well as maintaining or improving the associated catalytic performance is an area of significant focus. This work presents a comparative study of the catalytic activity of Pd-only, Pd/Rh and Rh-only catalyst systems with respect to CO, HC and NOx conversion. The Rh-only catalyst has been shown to have the potential to improve CO and NOx conversions when functioning as a downstream catalyst compared with a Pd/Rh catalyst as well as reducing the usage of precious metals. In addition the formation of the three way catalysis by-products N2O and NH3 in different catalyst systems was investigated. The temperature of N2O and NH3 formation was shown to correlate with NOx light off temperatures and to vary depending upon the catalyst system employed and ageing conditions. The Rh-only catalyst was shown to generate the highest amount of N2O and the Pd-only catalyst the highest amount of NH3.