Automotive catalysts

Abstract

Control and limitation of exhaust emissions from passenger cars is predominantly carried out using three-way catalytic converters (TWCs), which catalyse the transformation of these emissions, e.g. hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx), into more innocuous compounds like carbon dioxide (CO2), nitrogen (N2) and water. As catalytic active component, TWCs contain precious metals like platinum (Pt), palladium (Pd) and rhodium (Rh), belonging to the platinum group elements (PGE). With the spread of automotive catalysts and the development of environmental legislation (e.g. EURO phase I-V, US-EPA Tier 1-2 or California LEV I-II emission standards) the annual total demand of PGE for automotive catalysts increased continuously from 35 t in the year 1980 to 235 t in the year 2000 Expert-Verlag Renningen (Hagelken 2001-1). According to data from the EU commission, in 2002 approximately 16 million new passenger cars and light-duty commercial vehicles came into the european market (EU 2004). Today, in the most cases, the life span of the catalyst reaches that of the vehicle. Because of this, in the year 2000, 1,300 t PGE of the accumulated amount, mentioned above, was still in use in vehicles with a catalyst. This amount of PGE almost as large as 3.5 times of the annual primary production is an important PGE source for the automobile industry for the next years (Hagelken 2001-1). It is recognized that these precious metals are being spread into the environment to a still unknown extent, mainly due to surface abrasion of the catalyst during car operation. The final chemical form of these elements, their transformation in the environment and the repercussions of these transformations for living organisms are of paramount importance. Furthermore it is necessary that the automobile industry is enabled to assess the extent of the pollution at an early stage in order to make improvements in catalyst technology, either by stabilising the PGE more effectively (Palacios et al. 1999).