Promoted Pt catalysts in pollution control

Promoters are added to Pt catalysts because the promoted catalyst with modified electronic properties leads to a decrease in the activity for coke formation and also in the rate of metal sintering. Several promoted systems have been reported in the literature including for environmnetal pollution (vehicle exhaust emission) control and some are summarized here. 

100 faces with (100) planes. In contrast, in O2 and N2, polyhedral or spherical particles are observed. Data on the diffusion coefficient of the metals are very limited and much work needs to carried out in this area. Nevertheless Chojnachi and Schmidt (1989) have suggested that since Rh has the highest MR it might be expected to have the lowest diffusion coefficient. Diffusion through oxides could therefore be important in determining the difference in behaviour between Rh and Pd. 

Pt-Rh/AROs catalysts are widely used in automotive-exhaust emission control. In these systems, Pt is generally used for the oxidation of CO and hydrocarbons and Rh is active for the reduction of nitric oxide to N2. HRTEM and AEM show two discrete particle morphologies and Pt-Rh alloy particles (Lakis et al 1995). EM studies aimed at understanding the factors leading to deactivation, surface segregation of one metal over the other and SMSI are limited. There are great opportunities for EM studies, in particular, of surface enrichment, and defects and dislocations in the complex alloy catalysts as sites for SMSI. 

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