Catalytic Epoxidation of Propylene using Molecular Oxygen

The catalytic epoxidation of propylene with molecular oxygen represents a sustainable route to propylene oxide, a key precursor in polyurethane and polyether production. This process seeks to supplant traditional oxidants such as hydrogen peroxide or organic peroxides by employing air or O₂ directly, thereby reducing cost and environmental impact. Central challenges include achieving high selectivity to the epoxide over competing oxidation pathways that yield acrolein or carbon oxides, and operating under mild conditions to prevent catalyst deactivation. Progress hinges on tailoring active sites on metal and metal-oxide catalysts to balance oxygen activation, propylene adsorption and epoxide desorption. Mechanistic advances have revealed that both lattice oxygen and weakly-adsorbed oxygen species can drive epoxidation at distinct surface sites, while reactor–catalyst integration and doping strategies offer further avenues to enhance performance. The global significance of this reaction spans petrochemical manufacturing and green chemistry initiatives, with ongoing efforts to transition lab-scale breakthroughs to industrial practice.

Research from Nature Portfolio

Recent studies have demonstrated that finely tuned copper(I) oxide nanocrystals exhibit exceptional selectivity in propylene epoxidation with molecular oxygen. By engineering 27 nm cubic Cu₂O structures that expose {110} edge sites, researchers achieved propylene oxide selectivity exceeding 80 % at 90–110 °C. Detailed surface characterisation revealed that weakly-adsorbed O₂ species at the {110} edges facilitate a low-energy epoxidation pathway, while higher temperatures shift activity to lattice oxygen, leading to unwanted by-products. This work provides atomic-scale insight into site-specific oxygen activation and underscores the importance of surface facet engineering to optimise catalytic efficiency under mild gas-phase conditions.

Catalytic Epoxidation of Propylene using Molecular Oxygen publication trend

The graph below shows the total number of articles in catalytic epoxidation of propylene using molecular oxygen across all publications each year (not limited to Nature Index journals).

Technical terms

Epoxidation: Oxidation of an alkene to form an epoxide, introducing an oxygen atom across a carbon–carbon double bond.

Selectivity: The proportion of desired product formed relative to all products, reflecting catalyst performance.

Active site: A specific region on a catalyst surface where reactants adsorb and undergo chemical transformation.

Density functional theory (DFT): A computational quantum mechanical method used to model electronic structures of catalysts and reaction intermediates.

Allylic hydrogen stripping (AHS): A side reaction in propylene epoxidation where hydrogen is removed from the allylic position, leading to unsought by-products like acrolein.

Weakly-adsorbed oxygen species: Molecular oxygen that interacts lightly with catalyst surfaces, often facilitating lower-energy epoxidation pathways.

References

1. Fine cubic Cu2O nanocrystals as highly selective catalyst for propylene epoxidation with molecular oxygen. Nature Communications (2021).
2. Propylene Epoxidation using Molecular Oxygen over Copper- and Silver-Based Catalysts: A Review. ACS Catalysis (2020).
3. Gas-Phase Epoxidation of Propylene to Propylene Oxide on a Supported Catalyst Modified with Various Dopants. Catalysts (2019).