major global environmental treaty, the Montreal Protocol, to phase out CFC production by the turn of the century. A race by all CFC producers then began to find suitable and environmentally acceptable substitutes. The strategy is to reduce its atmospheric lifetime by introducing hydrogen into the molecule so that it is removed from the atmosphere by reaction with hydroxyl radicals in the troposphere. The commercially viable synthesis of these new compounds is a major challenge for catalysis, because catalysts used for the production of CFCs lack the required selectivity and activity to be acceptable for the production of hydrogen-containing substitutes.
The projected costs for these molecules, hydrogenated chlorofluorocarbons (HCFCs), are approximately 2-5 times those of the CFCs they are replacing, because of the complexity of the new manufacturing processes. Although rapid progress is being made toward the production of HCFCs, the latter are not entirely satisfactory and may have to be phased out in turn. Consequently, major advances in catalytic science and technology will be required to develop more acceptable substitutes before the turn of the century.
Catalytic technology is playing an ever-increasing role in environmental protection. In 1989, for the first time, the U.S. market for emission control catalysts (largely for automotive emissions) exceeded the market for petroleum refining catalysts. However, the area of stationary emission control (e.g., from power plants) has been flagged as one that will experience very large (20% per year) growth in the years ahead. There is also a need to reduce emissions from many chemical production plants. Thus, novel catalysis will in many cases be the critical technology that enables us to retain most of the benefits created by the chemical and petroleum industries, but with improved preservation of the environment.
Catalysts for automotive emission control are now well developed in the United States and, in general, meet mandated standards for removal of hydrocarbons, CO, and NOx. Recent Clean Air Act revisions will require significantly greater reductions in 1993 in the emissions of hydrocarbons, CO, and NOx, than those now mandated. In addition, very stringent local automobile emission standards (e.g., in California and Vermont) will require up to a 10-fold reduction in emissions by the late 1990s. This will necessitate more active catalysts, new catalyst supports (e.g., metallic supports), and new reactor designs that enhance low-temperature performance. A first step in this direction is the electrically heated converter, which offers a severalfold reduction in emissions over currently available technology. Because of the rapidly escalating price of rhodium (which promotes