Fine structural characterization of noble metals in washcoat of motorcycle three-way converter catalysts

Abstract

In Taiwan, over 14 million motorcycles exhaust vast amounts of pollutant gases, for which 24% of the total air pollutants cause significant air pollution in urban areas. The fine structures and the oxidation states of Pt/Pd/Rh/Ce species in washcoat catalysts of three-way motorcycle catalytic converters were investigated using EXAFS/XANES spectroscopy. Herein, a test of the federal test procedure (FTP) cycle for the deactivation of a motorcycle catalytic converter was conducted at running distances of 0, 5,000, 10,000, 15,000, and 30,000 km. Emissions of HCs pollutants were well controlled with Pt/Rh/Pd/Ce species supports on ceria/alumina washcoat owing to the exclusion of CO. The oxygen-rich environment leads to readily oxidized Rh and Pd species in the washcoat, while the Pt species are relatively difficult to oxidize. The Pd (Rh and Pt) species in the fresh and used washcoat catalysts have bond distances of 2.02 (2.03 and 1.90) and 2.75 (2.68 and 2.76) ± 0.02 Å and coordination numbers of 3.32 (5.70 and 4.13) and 11.81 (11.94 and 12.05) ± 0.05, respectively. Ceria species in washcoat catalysts are associated with the promotion of the crystalline phase to Ce(III) with a bond distance of 2.61 Å and a coordination number of 10.18 after 15,000 km catalyst FTP cycling. In addition, the transition metal is satisfactorily consisted with the La-O distances at about 2.49 Å.