Heterogeneous Catalysis and Fine Chemical Production (Green Chemistry)
Today tremendous pressure is currently exerted on chemical manufacturing industry to develop new synthetic methods that are environmentally more acceptable. For example, oxidation is an important industrial reaction but the current industrial practice is to use stoichiometric oxidants (manganates, chromates, etc) that generate a large quantity of inorganic pollutants. Our research is to seek cleaner alternative catalytic oxidation processes. We are working on a number of new approaches including the use of supported aqueous phase catalyst (SAPC) which concerns the creation of a thin water film carrying a homogeneous oxidation catalyst on a high surface area solid support in bulk organic solvent. SAPC substantially increase the interfacial surface area and provide an elegant way of heterogenising biphasic catalysts. Their main advantages concern easy catalyst recovery and increased activity. Selective oxidation of alcohols in supercritical carbon dioxide supercritical fluids (SCFs) is also under our intense investigation. We have recently shown that aerobic oxidation of alcohols to carbonyl compounds in scCO2 is an attractive, environmentally friendly alternative to the well-known aqueous phase oxidation on supported platinum metal catalysts. Mechanistic elucidation indicates that the favourable oxidative dehydrogenation of alcohol combined with readily desorption of lesser hydrophilic intermediates i.e. aldehyde prevent the alcohol from over-oxidation to acids with no detectable catalyst deactivation and no metal leaching (see Scheme 1) in supercritical fluid phase. Modify the hydrophobicity / hydrophilicity of the catalyst relative to the CO2 can also lead to significantly increase in conversion and catalyst stability.
Similarly, inorganic hydrides are conventionally employed for a wide range of important organic syntheses and many of them have proved to be excellent stoichiometric hydrogenation reagents. However, the preparation and regeneration of the highly toxic hydrides give separation and waste issues and so they are deemed unsuitable for the pharmaceutical and cosmetic industries in modern plants. Our approach is to carry out fundamental research to underpin the development of new but cleaner heterogeneous hydrogenation catalysts for their replacement.