is to reduce manufacturing costs by reducing raw material or processing costs.
The importance of catalyst synthesis is well illustrated by the recent development of high-activity catalysts for the reduction of nitrogen oxide (NOx) emissions from power plants. The material of choice for this application is titania-supported vanadia. In currently practiced technology, vanadia is dispersed into the pores of a titania monolith. A reaction engineering analysis of the performance of such catalysts has revealed that the catalyst operates in the diffusion-influenced regime and that the pore structure of the support can be optimized for maximum performance. Further research has shown that the desired pore structure cannot be achieved by using bulk titania because of physical strength constraints, but can be achieved by using silica. To obtain the chemical properties of titania required for high intrinsic activity, titania is dispersed into the pores of a silica monolith, and vanadia is then deposited on the titania particles. Based on laboratory-scale tests, the resulting material exhibits a catalytic activity 50% higher than that previously available and promises improved poison resistance due to its bimodal pore structure. This illustration shows the manner in which knowledge of material properties can be combined with an analysis of reaction dynamics and mass transfer to design a catalyst with optimal performance characteristics for a targeted application.
High selectivity in combination with high activity can often be achieved with homogeneous catalysts. These properties are influenced by the nature of the transition metal situated at the catalytically active center of the complex. Variations in the composition of the ligands and the solvent in which the complex is dissolved can influence the catalytic properties of the complex. Strategic manipulation of these variables can be used to obtain useful catalysts. A recent illustration of this point is the synthesis of naproxen, an anti-inflammatory drug. As currently manufactured, this drug is expensive because the synthesis procedure results in a mixture of the two optical isomers that must be separated, because S-naproxen is the desired product but R-naproxen is a liver toxin. To reduce the costs of production, one wants to increase catalyst selectivity for the S-isomer. Recent research has shown that naproxen can be produced with high selectivity by asymmetric hydrogenation of α-(6-methoxy-2-naphthyl) acrylic acid using a soluble ruthenium complex containing a chiral phosphine ligand. This advance holds promise not only for reducing the cost of production, but also for eliminating potentially harmful by-products.
Molecular sieves, of which zeolites are a special class, offer extensive opportunities for the design of new catalysts. These materials are characterized by a crystalline framework containing cavities and channels of molecular dimensions (0.3-1.0 nm). Catalytic activity is typically due to acidic