Improving sustainability of industrial catalysts
Worldwide, the majority of carbon-based materials as well as energy is produced by oxidative conversion of the alkanes in petroleum or natural gas. However, the high strength of the carbon–hydrogen (C-H) bond in alkanes requires extreme temperatures leading to low conversion efficiencies and high emissions. Catalysts that perform better under environmentally benign conditions and at a reasonable cost could have a major impact on industry. Transition metal complexes can act in a way similar to enzymes. Scientists initiated the EU-funded project 'Development of sustainable selective catalytic oxidation of alkanes' (OXALKANES) to exploit them. Researchers developed transition metal complexes from transition metals of Period 4 of the Periodic Table of Elements (e.g. iron, cobalt, copper). They applied them as selective homogenous and heterogeneous catalysts in C-H activation reactions at room temperature with oxygen supplied by environmentally benign hydrogen peroxide. Yield was increased with microwave assistance. Cyclohexane oxidation produced cyclohexanone and cyclohexanol with higher yields than achieved with conventional catalysts and under mild and sustainable conditions. The main products were used as precursors in the synthesis of value-added products such as Nylon-6, a component widely used in industrial yarns, textiles, and plastic films for the food and energy industries. Oxidation of benzene yields phenol as the main product, an important intermediary in the synthesis of petrochemicals, agrochemicals and plastics. Direct oxidation of benzene to phenol is generally plagued by low yields and/or poor catalyst selectivity. OXALKANE scientists demonstrated higher selectivity than conventional catalysts and yields equal to or better than those reported in the literature with their homogeneous and heterogeneous catalysts. Overall, OXALKANES' novel transition metal complexes enabled oxidation of alkanes under mild and sustainable conditions, and with comparable or higher yields than conventional catalysts and methods. They are expected to make an important contribution to numerous industrially relevant oxidation processes by increasing sustainability while decreasing environmental impact.
