Development of Solid Catalysts

In Table 1.2 selected solid catalysts are shown together with their main use. Bulk and supported catalysts as well as zeolite-based catalysts are listed. Many of the examples shown have been known for decades. However, a continuous and spectacular progress over the years is noted for many catalytic processes. We discuss two examples hereafter. 

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The small amounts of solid catalysts purchased by the fine-chemical industry means that contact between the catalyst producers and the fine-chemical industry is usually very limited. Often the fine-chemical industry does not wish to inform the catalyst producer about the specific reaction that is to be performed with the catalyst. Although there is much room for the development of better catalysts, there is no commercial incentive to improve the situation. Elucidation of the fundamental principles underlying the activity and selectivity of solid catalysts in the liquid-phase reactions characteristic of many fine-chemical processes might lead to the development of solid catalysts better adapted to specific processes. 

Development of Solid Catalyst Synthesis Table 1.3 Generations of solid catalysts according to manufacturing techniques. 

The major impetus for the development of solid phase synthesis centers around applications in combinatorial chemistry. The notion that new drug leads and catalysts can be discovered in a high tiuoughput fashion has been demonstrated many times over as is evidenced from the number of publications that have arisen (see references at the end of this chapter). A number of )proaches to combinatorial chemistry exist. These include the split-mix method, serial techniques and parallel methods to generate libraries of compounds. The advances in combinatorial chemistry are also accompani by sophisticated methods in deconvolution and identification of compounds from libraries. In a number of cases, innovative hardware and software has been developed tor these purposes. 

This section discusses the techniques used to characterize the physical properties of solid catalysts. In industrial practice, the chemical engineer who anticipates the use of these catalysts in developing new or improved processes must effectively combine theoretical models, physical measurements, and empirical information on the behavior of catalysts manufactured in similar ways in order to be able to predict how these materials will behave. The complex models are beyond the scope of this text, but the principles involved are readily illustrated by the simplest model. This model requires the specific surface area, the void volume per gram, and the gross geometric properties of the catalyst pellet as input. 

The EM studies show that the novel glide shear mechanism in the solid state heterogeneous catalytic process preserves active acid sites, accommodates non-stoichiometry without collapsing the catalyst bulk structure and allows oxide catalysts to continue to operate in selective oxidation reactions (Gai 1997, Gai et al 1995). This understanding of which defects make catalysts function may lead to the development of novel catalysts. Thus electron microscopy of VPO catalysts has provided new insights into the reaction mechanism of the butane oxidation catalysis, catalyst aging and regeneration. 

We consider a reactor with a bed of solid catalyst moving in the direction opposite to the reacting fluid. The assumptions are that the reaction is irreversible and that adsorption equilibrium is maintained everywhere in the reactor. It is shown that discontinuous behavior may occur. The conditions necessary and sufficient for the development of the internal discontinuities are derived. We also develop a geometric construction useful in classification, analysis and prediction of discontinuous behavior. This construction is based on the study of the topological structure of the phase plane of the reactor and its modification, the input-output space. 

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