Automotive Catalysts: Performance, Characterization and Development

Abstract

Nowadays, automotive catalysts have been used to reduce atmospheric emissions, due to significant parcels of the global emissions of pollutants agents provoked by vehicles. Automotive exhaust catalysts were introduced in the 70’s decade, because some countries established restricting laws related to emissions of carbon monoxide (CO), nitrogen oxides (NOx) and hydrocarbons (HC) by the engines. These products generated by the combustion process are extremely harmful to health and the environment (Massad et al, 1985). For example, CO combined with hemoglobin in the bloodstream promotes the reduction of oxygen-active sites that provokes asphyxia. Nitrogen dioxide (NO2) contributes to photochemical smog and acid rain, and is irritating to the eyes, skin and respiratory system. Nitrogen monoxide (NO) is toxic by inhalation and irritating to the eyes and skin. Polycyclic aromatic hydrocarbons (PAHS) have been identified as carcinogenic compounds. Other combustion products are: ash, formed mainly by particulate residues of components of the lubricating oil, and soot, combustible matter in the exhaust gas (smoke). Automotive catalytic converters have been developed precisely to make these products less toxic (Morterra et al, 1995; Ismagilov et al, 1998). The development of catalysts only was possible with the improvement in automotive engines as the replacement of carburetion system for electronic injection and introduction of the catalyst in the exhaust systems (Kaspar et al, 2003). The catalysts of three ways (TWC –Three-Way Catalyst) are advanced systems of emission treatment of gasoline vehicles that reduce significantly the emissions of carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NOx) in atmosphere (Collins & Twigg 2007). Nevertheless, there is a steady increase in world production of vehicles powered by gasoline and by other types of fuel such as alcohol, gas and mix of fuel, leading to constant research in order to improve the catalysts already known and to develop new models (Mizukami et al, 1991; Silva et al, 2009 & Sideris, 1997). Automotive catalysts are generally available in the form of monolith ceramic as cordierite and zeolites or metal substrate. The catalyst substrates more used are composed of magnesium cordierite (2MgO.2A12O3.5SiO2) with a honeycomb structure, which provides a high geometric surface area, coated with γ-alumina (catalyst wash-coat). This wash-coat is designed to increase the specific surface area and is the support for precious metals, mainly platinum (Pt), palladium (Pd) and rhodium (Rh), which promotes the catalytic reduction and oxidation of