In Chemistry, a catalyst is defined as any substance that increases the rate of a reaction without itself being consumed. They achieve this by providing a thermodynamic pathway of lower energy than the standard required to convert the reactants into products. Chemists have developed an arsenal of catalyst systems for an array of compounds to produce desirable materials in many conditions and at many scales of production.
Catalysts can be largely categorized into 2 sub-categories: homogeneous and heterogeneous; homogeneous catalysts are defined as being in the same phase as the reactant whilst heterogeneous catalysts are defined as being in a separate phase to the reactants. These properties inform how they are used, and particularly whether they can be recycled for future use with more reactants. In general, heterogeneous catalysts, such as solid catalysts in liquid media, are better for larger scale, bulk reactions, capable of many uses before mechanical attrition and chemical change render it less efficacious or potentially changes what products it produces; homogeneous catalysts by comparison lend themselves to smaller scale, batch reactions producing specific compounds where catalyst recovery is less important than the results of that reaction.
Designing a catalyst with the benefits of both homogeneous and heterogeneous systems poses an interesting and rewarding challenge. We attempted to tether an organometallic iridium catalyst, used in transfer-hydrogenation reactions, to organomodified silica nanoparticles.
Several approaches were investigated: catalyst attachment directly to silica nanoparticles using a silica coating agent; monomers functionalized with a chain-transfer agent, attached and brush polymers grown out of the silica nanoparticle resulted in sub-optimal results. Ultimately, functional brush polymers grown on silica particles using functional oligomers yielded the most consistent, reproducible and ultimately promising results, including demonstration of quantitative attachment of the catalyst to the brush polymer.
