Platinum-group elements: quantification in collected exhaust fumes and studies of catalyst surfaces

Automotive catalytic converters, in which Pt, Pd and Rh platinum-group elements; PGEs. are the active components for eliminating several noxious components from exhaust fumes, have become the main source of environmental urban pollution by PGEs. This work reports on the catalyst morphology through changes in catalyst surface by scanning electron microscopyrenergy dispersive X-ray spectroscopy SEMrEDX. and laser-induced breakdown spectrometry LIBS. from fresh to aged catalytic converters. The distribution of these elements in the fresh catalysts analysed Pt]Pd]Rh gasoline catalyst. is not uniform and occurs mainly in a longitudinal direction. This heterogeneity seems to be greater for Pt and Pd. PGEs released by the catalysts, fresh and aged 30 000 km, were studied in parallel. Whole raw exhaust fumes from four catalysts of three different types were also examined. Two of these were gasoline catalysts Pt]Pd]Rh and Pd]Rh. and the other two were diesel catalysts Pt.. Samples were collected following the 91441 EUDC driving cycle for light-duty vehicle testing. The results show that at 0 km the samples collected first have the highest content of particulate PGEs and although the general tendency is for the release to decrease with increasing number of samples taken, exceptions are frequent. At 30 000 km the released PGEs in gasoline and diesel catalysts decreased significantly. For fresh gasoline catalysts the mean of the total amount released was approximately 100, 250 and 50 ng kmy1 for Pt, Pd and Rh, respectively. In diesel catalysts the Pt release varied in the range 400]800 ng kmy1. After ageing the catalysts up to 30 000 km, the gasoline catalysts released amounts of Pt between 6 and 8 ng kmy1, Pd between 12 and 16 ng kmy1 and Rh between 3 and 12 ng kmy1. In diesel catalysts the Pt release varied in the range 108]150 ng kmy1. The soluble portion of PGEs in the HNO3 collector solution represented less than 5% of the total amount for fresh catalysts. For 30 000 km the total amount of soluble PGEs released was similar or slightly higher than for 0 km.