Selective and mild O₂-driven biocatalytic reactions are of great relevance for sustainable chemical synthesis since molecular oxygen is a cheap, abundant and non-hazardous oxidant. Furthermore, O₂ as oxidant leads mostly only to the formation of water or hydrogen peroxide as by-product. However, utilization of O₂ as oxidant in biocatalytic reactions is still hampered by several limitations. First, an efficient supply of the enzyme with O₂ is challenging due to the low solubility of O₂ in the aqueous medium. Secondly, gas-liquid-interfaces introduced by aeration or stirring inactivate most biocatalysts. Finally, the formation of reactive oxygen species decreases stability and activity of the involved biocatalysts. We aim to address these challenges by increasing the stability of O₂-biocatalysts via enzyme-engineering approaches, decreasing the K_M for molecular oxygen and optimising the reaction procedures using process engineering. We intend to focus on O₂-dependent NADH-oxidases (NOXs) as modular biocatalysts. NOX is utilized to recycle reduced nicotinamide-based cofactors; previously we could show their application in multi-enzymatic cascades to convert renewable raw materials into chemicals. We will use different approaches to engineer NOXs on a molecular level such as directed evolution and DNA shuffling to improve the efficiency and stability. The process engineering part will involve process simulations and testing different reactor types to define the optimal parameters for an efficient use of NOXs as well as novel biocatalytic cascades. The outcome will provide a new platform to be used for large-scale production of chemicals by oxidative biocatalytic cascades from renewables and O₂.