Engineering Tetrahedral Co2+-Exposed Co3O4 Nanosheets toward Highly Efficient Styrene Epoxidation

Styrene oxide, an important intermediate, is of great significance in fine-chemical synthesis. Great efforts have been made to design novel catalysts for styrene oxide synthesis by styrene epoxidation reaction (SER). Recently, Co3O4 has been considered as an attractive alternative to the noble catalysts for efficient SER. However, there are two potential catalytic sites within Co3O4: tetrahedral Co2+ and octahedral Co3+. It is highly desirable to identify the catalytic insight into the geometric sites and engineer highly efficient Co3O4 catalysts. Herein, we engineered anisotropic Co3O4 (A-Co3O4) nanosheets, which primarily exposed tetrahedral Co2+ on the surface. It exhibited an enhanced SER catalytic performance in the styrene oxide yield by a factor of 5.69, compared with site-exposed isotropic Co3O4 (I-Co3O4). The CoAl2O4 experiment shows that tetrahedral Co2+ is more beneficial to trigger SER than octahedral Co3+, thus maintaining the styrene oxide yield. The density functional theory calculation results further show that tetrahedral Co2+ is more conducive to the styrene oxide synthesis by comparing the free energy change of the SER rate-determining step. Thus, this work uncovers the site-dependent catalytic essence and paves the way for the implementation of facet engineering toward highly efficient catalysis.