catalyst results in products worth 2000 times its own value during its useful life.

The refining of petroleum to produce fuels for heating and transportation involves a large number of catalytic processes. One of these is the catalytic reforming of naphtha, a component derived from petroleum, used to produce high-octane gasoline. In modern catalytic reforming, many different catalytic reactions proceed on small particles made of platinum and a second metal such as rhenium or iridium. These bimetallic clusters are expensive but chemically robust. They can be reactivated after long-term use, thus making possible the use of precious metals to produce an affordable consumer commodity. The metallic clusters are so small that practically all metal atoms are exposed to the reactants and take part in the catalytic cycle. These metal clusters are supported within the pores of an acidic metal oxide that also takes part in the reforming process.

The next illustration of catalysis shows that industrial catalysts can be biomimetic, in the sense that they imitate the ability of enzymes to produce optically active molecules (i.e., molecules whose structures are such that the reflection of the molecule in a mirror does not superimpose on the original molecule). Many pharmaceuticals are known to be active in only one form, let us say the left-handed form. It is therefore critical to obtain the left-handed form with high purity. This is particularly important when the drug is toxic, even if only slightly so, and must be administered over many years. It is true of a molecule called L-Dopa used in the treatment of Parkinson's disease. Here, the right-handed molecule is inactive. In ordinary synthesis, both forms (right and left) are produced in equal amounts. Their separation is costly. Is it possible to produce only the left-handed form by means of a synthetic catalyst? The first success of an industrial synthesis of this kind was achieved at Monsanto, and a patent for the selective synthesis of L-Dopa was granted in 1974. The catalytic process used to make L-Dopa today may be regarded as an important achievement in industrial catalysis.

Finally, more recent developments in catalytic technology are targeted at the protection of the environment. The best-known example deals with catalytic converters that remove pollutants from the exhaust gases of automobiles. Catalytic converters for automobiles were first installed in the United States in the fall of 1974. These devices were subsequently introduced in Japan and are currently spreading through Europe. The most advanced catalyst now contains three metals of the platinum group and controls the emissions of carbon monoxide, nitrogen oxides, and unburned hydrocarbon molecules by use of a complex network of catalytic reactions. This application has contributed more than any other to public awareness of catalysis and of its many applications for the benefit of mankind.



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