Environment catalytic converters

The protection of the environment implies the elimination of lead compounds, first of all because of their individual toxicities and second because these derivatives or their products of decomposition poison catalytic converter catalysts. 

In principle, the catalytic converter is a fixed-bed reactor operating at 500—620°C to which is fed 200—3500 Hters per minute of auto engine exhaust containing relatively low concentrations of hydrocarbons, carbon monoxide, and nitrogen oxides that must be reduced significantly. Because the auto emission catalyst must operate in an environment with profound diffusion or mass-transfer limitations (51), it is apparent that only a small fraction of the catalyst s surface area can be used and that a system with the highest possible surface area is required. 

The release of PCDD/PCDF from transport activities was estimated to be very minimal and not reported for uncontrolled combustion processes (Universiti Sains Malaysia, 2004). In the Department of Environment Malaysia 1997 report, the major sources of air pollution in 1996 were motor vehicles, 82%, power stations, 9%, industrial fuel burning, 5%, industrial production processes, 3%, domestic and commercial furnaces, 0.2%, and open burning at solid waste disposal sites, 0.8% (Afroz et al., 2003). Leaded gasoline has been phased out since 1998 and most cars have been fitted with catalytic converters since then. Consequently, a minimal release of PCDD/PCDF is expected from motor vehicles that are mainly from diesel-powered vehicles. The released air pollutions monitored were CO, N02, S02, 03, and suspended particulate matters. 

ICP-MS is useful for analysis of catalysts from two perspectives The composition of the catalysts must be carefully controlled, particularly because the active elements are often expensive. The catalysts are often finely distributed in a substrate material so their concentration in the bulk material may be quite low. Second, catalysts, particularly those used in automotive catalytic converters, can be a significant source of platinum group elements in the environment. Re and Pt have been measured in catalysts by ICP-MS [193], Procedures for the analysis of used catalytic converter materials by ICP-MS have been reported [355]. Accurate measurements are essential for many of these applications so isotope dilution-based concentration calibration is commonly used. 

It has been demonstrated that catalytic converters are responsible for releasing considerable amounts of Pt ant Pd to the urban environment (Cicchella et al, 2003, 2008a Schafer and Puchelt, 1998 Zereini et al, 1994), which has caused an increase in the incidence of allergies and problems related to the respiratory system (Rosner and Merget, 2000 Von Hoff et al, 1976). 

Figure 11.1. Possible pathway of PGEs from car catalytic converters to the environment and food.

E. Helmers, Platinum emission rate of automobiles with catalytic converters D comparison and assessment of results from different approaches, Environ. Sci. Pollut. Res., 4 (1997), 100D103. 

S. Caroli, A. Alimonti, F. Petrucci, B. Bocca, P. Schramel, M. Zischka, C. Pettersson, U. Wass, M. Luna, J. C. Saenz, J. SantamarEnvironmental risk of particulate and soluble platinum group elements released from gasoline and diesel engine catalytic converters, Sci. Total Environ., 296 (2002), 199D208. 

R. Merget and G. Rosner, Evaluation of the health risk of platinum group metals emitted from automotive catalytic converters, Sci. Total Environ., 270 (2001), 165D173. 

Tetraethyl lead (TEL), formula (CH3CH2)4Pb, was once added to gasoline to increase the octane rating and lubricate the valves. In the 1970s lead was banned from automotive gasoline because it inactivates catalytic converters and introduces lead into the environment. TEL is still used in DOLL, which is low-lead 100-octane aviation fuel for piston aircraft engines. Mo suitable replacement fuel has yet been certified for the old engines. 

Bagley, S. T., Gratz, L. D., Johnson, J. H., and McDonald, J. F. 1998. Effects of an Oxidation Catalytic Converter and a Biodiesel Fuel on the Chemical, Mutagenic, and Particle Size Characteristics of Emissions from a Diesel Engine. Environ. Sci. Technol., 32,1183-1191. 

Watts S. F. and Roberts C. N. (1999) Hydrogen sulfide from car catalytic converters. Afmoi. Environ. 33(1), 169—170. 

Concerns for our environment have made a huge impact in the products and processes we use every day. The catalytic converter is one of those impacts. 

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