Automotive emission control catalysts

The main areas of commercial apphcation are automotive emission control catalysts (autocatalysts), oil refining, ammonia oxidation, hquid-phase ... 

Automotive Emission Control Catalysts. Air pollution (qv) problems caused by automotive exhaust emissions have been met in part by automotive emission control catalysts (autocatalysts) containing PGMs. In the United States, all new cars have been requited to have autocatalyst systems since 1975. In 1995, systems were available for control of emissions from both petrol and diesel vehicles (see Exhaust control, automotive). 

Rosner, G., and Merget, R. (2000). Evaluation of the health risk of platinum emissions from automotive emissions control catalysts. In Anthropogenic Platinum-Group Element Emissions. Their Impact on Man and Environment (F. Zereini and F. Alt, eds.), pp. 267—281. Springer-Verlag, Berlin. 

Fig. 41). Changes in emission legislation and in automotive emission control catalyst technology therefore might affect both the supply and the price of platinum, palladium and especially rhodium (Table 12). 

Tables 13 and 14) [31]. These countries report huge reserves, but with different mine ratios of Pt to Pd to Rh (Table 15). The concentration of Pt, Pd and Rh in the raw ore is reported to be in the order of magnitude of a few parts per million, whereas their concentration in automotive catalysts is in the order of magnitude of about 3 000 ppm for Pt and about 600 ppm for Rh. These aspects contribute to the increasing interest in the recycling of the precious metals out of used automotive emission control catalysts. By 1996 about 16% of the platinum demand for automotive catalysts, about 5% of the palladium demand and about 10% of the rhodium demand for automotive catalysts was supplied from the recycling of these catalysts [32, 33],... 

Figure 44. Model gas reactor to study the activity of automotive emission control catalysts.

A very drastic and common deactivation phenomenon with automotive emission control catalysts is the irreversible mechanical destruction of the support during road use by breakage in the case of ceramic monoliths, by telescoping of the matrix or breakage of the foil in the case of some metallic substrates and, formerly, by attrition in the case of bead catalysts. With ceramic monoliths, sudden temperature changes can cause thermal stresses and consequent breakage. 

High performance automotive emission control catalysts are a combination of the compromises required by the sometimes opposing requirements of their highly... 

Since 1975, CATALYSIS has been the only practical way for automotive manufacturers to meet the severe regulation of exhaust gas emission in JAPAN and in the U.S. Similar measures will be applied in Europe in the near future. For numerous economic and technical reasons, automotive emission control catalysts are supported catalysts. This means that the active phase is dispersed on the surface of a catalytically almost inert material. That material is the subject of this investigation. 

The Chemistry of Degradation in Automotive Emission Control Catalysts... 

Oxidative Automotive Emission Control Catalysts—Selected Factors Affecting Catalyst Activity... 

Tn the development of oxidative automotive emission control catalysts for use in the 1975 model year, certain requirements were recognized from the beginning. The catalyst had to be physically rugged and capable of withstanding both the mechanical and thermal abuse to which it would be subjected in an automobile driven by average drivers on real roads. The catalyst had to exhibit high levels of activity so that the catalytic units would be of reasonable size. The catalyst had to be stable for at least 50,000 miles and capable of withstanding chemical abuse from the exhausts of the various fuels to which it would be subjected. 

Some of the factors affecting the activity and durability of automotive emissions control catalysts were studied. It was found that at... 

The trends mentioned above can be important in the case of automotive emission-control catalysts. By using suitable supports, it is possible to achieve the same catalyst performance with smaller amounts of noble metals. The latter is crucial for Rh which is an expensive and scarce noble metal [15]. 

The results of a development program for Pd-only and Pd/Rh automotive emission control catalysts are discussed. A review of former experiences with Pd-containing systems, especially their poor tolerance against lead and sulfur poisoning is given. Model gas experiments were conducted with improved Pd-based catalysts. Not only the activity to convert simultaneously CO, NO and hydrocarbons (HC) was investigated, but also the formation of so-called secondary emissions such as N2O or NH3. 

But on a long term basis a major increase of the amount of Pd used in automobile converters might change the price situation completely. Indeed, presently only 9 % of the Pd available to the market is used in automotive emission control catalysts. In case of Pt this share is about 45 %, whereas the world supply of Pt and Pd is in the same order of magnitude, see Figure 2. 

Cerium-zirconium mixed metal oxides are used in conjunction with platinum group metals to reduce and eliminate pollutants in automotive emissions control catalyst systems. The ceria-zirconia promoter materials regulate the partial pressure of oxygen near the catalyst surface, thereby facilitating catalytic oxidation and reduction of gas phase pollutants. However, ceria-zirconia is particularly susceptible to chemical and physical deactivation through sulfur dioxide adsorption. The interaction of sulfur dioxide with ceria-zirconia model catalysts has been studied with Auger spectroscopy to develop fundamental information regarding the sulfur dioxide deactivation mechanism. 

---