Molecular science, catalyst design

Science of catalysts has much to learn from materials science of metals, alloys, ceramic materials, and semiconducting materials. In turn, because catalytic science is practiced on a molecular nanostructure and surface submonolayer scale, it is one that is at the cutting edge of materials science in general and will no doubt have its impact on the technology of new, catalytic and non-catalytic materials. This symposium volume demonstrates that the field is well and alive and that progress toward a scientific catalyst design is substantial. 

Somorjai, G. A. In The Building of Catalysts A Molecular Surface Science Approachf in Catalyst Design. Progress and Perspectives John Wiley Sons, New York, 1987, Chapter 2 11-69. 

The performance of a catalyst is determined by its lifetime, activity and selectivity in converting raw materials into end products. Therefore, the design objectives are to satisfy the requested parameters for these properties. From the computational chemistry point of view, there are several different approaches in the research of catalyst design applic ion of databases and expert systems, chemistry of the catalytic process, in the nonmolecular field, and the many aspects of molecular science. 

The objectives of catalyst design are to improve the catalytic performance, defined by lifetime, selectivity, and activity, Utilization of data bases and expert systems will continue to be the first step and will develop towards the application of new information sciences. Chemistry of the catalytic process is playing an important practical role in industry. The integration with molecular and material science is a natural extension. The molecular science approach is now able to provide insight into structures and mechanisms at the atomic level. 

An important future goal of catalytic surface science is to monitor the structure of surfaces and adsorbates at the molecular level in situ under catalytic reaction conditions, to model the more complex technical catalysts, and to undertake the design and tuning of new catalyst surfaces. 

Since its discovery more than 50 years ago, olefin metathesis has evolved from its origins in binary and ternary mixtures of the Ziegler-Natta type into a research area dominated by well-defined molecular catalysts. Surveys of developments up to 1993 were presented in COMC (1982) and COMC (1995). Major advances in ROMP over the last 10 years include the development of modular, stereoselective group 6 initiators, and easily handled, functional-group tolerant ruthenium initiators. The capacity to tailor polymer functionality, chain length, and microstructure has expanded applications in materials science, to the point where ROMP now constitutes one of the most powerful methods available for the molecular-level design of macromolecular materials. In addition to an excellent and comprehensive text on olefin metathesis, a three-volume handbook s has recently appeared, of which the third volume focuses specifically on applications of metathesis in polymer synthesis. 

In addition to a large catalytically active surface and good capacity for adsorption, an efficient catalyst requires selectivity, that is, preferential affinity for the appropriate reactants. Nonselectivity is a source of significant problems in catalysis, particularly in the petrochemical industry, which has to deal with hydrocarbons of various types and isomers in a single stream. This situation has provided a strong incentive for the development of artificial (man-made) catalysts that offer the type of selectivity unthinkable on metal surfaces discussed in the last section of Chapter 9 (see, for example, Ball 1994) and illustrates another example of molecular design (or molecular engineering ) of advanced materials for use in science and industry. 

The innate complexity of practical catalytic systems has lead to trial and error procedures as the common approach for the design of new and more proficient catalysts. Unfortunately, this approach is far from being efficient and does not permit to reach a deep insight into the chemical nature of the catalytic processes. The consequence of this difficulty is a rather limited knowledge about the molecular mechanisms of heterogeneous catalysis. To provide information about catalysis on a molecular scale, surface science experiments on extremely well controlled conditions have been designed and resulted in a new research field in its own. However, even under these extremely controlled conditions it is still very difficult, almost impossible, to obtain precise information about the molecular mechanisms that underlie catalytic processes without an unbiased theoretical guide. The development of new and sophisticated experimental techniques that enable resolution at... 

Every 25 years or so, there appears to be a quantum jump in polyolefin technology. Metallocene catalysts are considered by many to be one such revolution in polymer science. They have been referred to as designer catalysts, because of their ability to polymerize an incredible variety of olefin monomers to form copolymers with different microstructures, narrow (uniform) molecular weights and reproducible distributions... 

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