Fine Cubic Cu2O Nanocrystals Enable High Selectivity Catalysis for Propylene Epoxidation

Propylene oxide (PO) is a valuable intermediate product in chemical industry. Current industrial production of PO is neither cost-effective nor environmentally friendly. Propylene epoxidation with O₂ to PO can mitigate such drawbacks. However, its practical application is hindered by a lack of efficient catalyst with high selectivity.

The research team led by Prof. HUANG Weixin from the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences constructed fine cubic Cu₂O nanocrystals that enabled high selectivity catalysis for propylene epoxidation. The mechanism that endowed Cu₂O nanocrystal with such enhanced catalytic performance was also demonstrated. This work was published in Nature Communications.

Based on their previous study on Cu₂O catalysts, the researchers speculated that Cu₂O{110} edges might be crucial in propylene epoxidation reactions. (Angew Chem Int Ed., Angew. Chem. Int. Ed.) However, large rhombic dodecahedral Cu₂O nanoparticles have insufficient {110} edges, while Cu₂O cubes finer than 100 nm are much richer in {110} edges. This interesting size effect was utilized in this study.

In this work, utilizing the size effect researchers previously found, they synthesized Cu₂O cubes with an average size of 27 nm, which showed an outstanding PO selectivity at a relatively low temperature. It was confirmed that the abundant Cu₂O{110} site was the active site for PO production. Further investigations into the catalytic mechanism discovered a temperature-dependent behavior for the catalyst. Under low temperatures, the reaction was dominated by Langmuir-Hinshelwood (LH) mechanism, in which weakly adsorbed O₂ species served as active oxygen species. While under high temperatures, Mars-van Krevelen (MvK) mechanism played the major role. CO₂ and acrolein were also formed as by-products, which undermined the PO selectivity of the catalyst.

The development of the catalyst with high PO selectivity in propylene epoxidation offers a new approach to designing efficient catalyst for propylene epoxidation.