| Research Abstract |
Since automobiles equipped with three-way (i.e. removing carbon monoxide, nitrogen oxides, and hydrocarbons together in exhaust gasses) catalysts run under strict conditions as 400-1000 ℃, platinum, palladium, and rhodium are released by catalytic degradation, causing an environmental pollution. Then, the emissions of these precious metals in soot from the exhaust pipes and mufflers of 4 types of gasoline powered cars, were investigated first and ascertained that the values were Pt : 11-32 ppm, Pd : 7-19 ppm, and Rh : 3-25 ppm, respectively. The content of these precious metals tends to increase with increasing the running distance (50,000-130,000 km) of cars in roads, and also with drawing to the three-way catalytic converter in exhaust pipes.
In soot samples, Pd and Rh were detected in M IRA (DAIHATSU), while Pt and Rh were detected in FAMILIA (MAZDA), SUNNY (NISSAN), and SKYLINE (NISSAN), respectively. Inorganic ingredient (10.7-5,440 ppm) detected except for precious metals in soot
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of SKYLINE (running distance : 130,000km, 1992 type) were Na, Ca, Fe, Zn>Al>Si>Mg, Mn, Ni>Ce>V, Zr, etc, while Ba, Co, La, and Mo were under detection limit.
In environmental samples involving soot of cars and dusts, as soil and moss (Bryum argenteum Hedw.) in major road ways (national road, the 8 line, Imamaehi, Kanazawa), Pd (29-59 ppb) and Rh (15-34 ppb) were detected within 1m from the edge of the white line of automobile road, while Pt were under detection limit (<8ppb). This results indicate that these precious metalt particles emitted from motor vehicles are relatively heavy, and don't travel far from car exhaust pipes, falling out at the edges of roadways. In road ways of tunnel (national road, the 157 line, Higashifutaguchi and Kuwajima, near Tedori dam, Ishikawa), Pd (26-84 ppb) and Rh (230-1,700 ppb) were detected within 1 m from soil and soot of the inside wall, while Pt was under detection limit (8 ppb).
Solubility of Pd and Rh in soot from the exhaust pipe and mufflers using 0.1 M hydrochloric acid were <1%, while that of Pt was not observed. This result suggests that a small amount of Pd and Rh is in chloride species. Less
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