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The selectivity and activity of homogeneous catalysts under mild reaction conditions is unbeaten by their heterogeneous counterparts. Unfortunately, the problem of seperating the single-site catalysts from the reaction media is still an important hurdle for large scale applications in industry. In most cases, the development of materials combining the advantages of classical homogeneous and heterogeneous catalysts has remained an elusive goal.
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We have pioneered the development of an entirely new chemical technology for catalysis. This technology bridges the property space between hydrocarbon-ligated metal complexes and oxidic supported catalysts. It imparts new or improved properties to catalytic materials achieving uncannily precise molecular architectures. Our single site catalysts are derived from chemicals known as polyhedral oligomeric silsesquioxanes rendering POSS® metal derivatives. POSS® catalysts have unique features:
- The chemical composition of the support is a hybrid, intermediate (RSiO1.5) between that of silica (SiO2) and silicones (R2SiO). The support is electron withdrawing and increases Lewis acidic catalyst activity.
- POSS® catalysts can contain one or more covalently bonded reactive functionalities suitable for polymerization, grafting, surface bonding, or other transformations covering the generation of precise catalytic materials and catalyst supports.
- POSS® catalysts are physically large and range approximately 1-3nm in size. They can be molecularly enlarged (POSS® building block chemistry) to cover applications from homogeneous catalysis via membrane catalyst retention to truly heterogenous catalysis, either in gas or liquid phase application.
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 Polyhedral oligomeric silsesquioxanes (abbreviated to POSS) may overcome the problems encountered in homogeneous catalysis. POSS catalysts are of nanoscopic size and can be built stepwise. Furthermore, they can be made on a large scale with functionalities for immobilisation. In this way, well-defined heterogeneous catalysts can be achieved that incorporate the advantages of homogeneous catalysts (both catalyst and reactant in the liquid phase, thus avoiding mass-transfer limitations) and heterogeneous catalysts (using nanofiltration, a POSS catalyst can easily be separated from reaction products). Reproducibility and quality of catalyst synthesis are assured through the precise nature of POSS.
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POSS Nanostructured Catalysts exemplify a chemical nanotechnology. The precise size of cage, composition and metal incorporation is defined by exact formula weights and molecular representations. Reproducibility and quality of catalyst synthesis are assured through the precise nature of POSS. Well-defined POSS metal libraries illustrate the potentially wide window for POSS Nanostructured Catalyst applications.
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