En route to complete design of heterogeneous catalysts

Achieving complete control in the synthesis of the active center of a heterogeneous catalyst, which includes the active site, environment around the active site, and the access path is highly desirable but not attainable yet. However, there has been significant progress in recent years that permits a level of control of these properties that are unachievable before. Some illustrative examples are described to demonstrate this in the synthesis of active sites in metal and oxide catalysts and their surroundings. For the active site synthesis, examples include using polynuclear metal complexes as precursors, cluster beam deposition, and use of dendrimers to generate metallic active sites, protection of coordination unsaturation in the synthesis of oxide active sites, and employing silsesquioxane, and unit-by-unit approach. Exfoliation, use of inverse micelles, molecular and macromolecular templating as techniques to exert control of the environment of the active center are also discussed. The limitations of these synthetic methods and remaining challenges are examined.