Synergistic regulation of the Co microenvironment in MOF-74 for olefin epoxidation via lanthanum modification and defect engineering†

Abstract

The fine design and regulation of the microenvironment surrounding active sites in metal–organic frameworks (MOFs) are crucial for optimizing electron distribution and enhancing oxygen activation, thereby achieving superior catalytic performance in epoxidation reactions. In this study, we focus on the synergistic modulation of the cobalt (Co) microenvironment in MOF-74 through the introduction of lanthanum (La) sites and defect engineering. The incorporation of rare-earth La species effectively redirects the electron density of Co sites, enhancing their oxygen activation capabilities. Additionally, the presence of coordination-unsaturated Co sites facilitates rapid electron transfer from active sites to substrates, promoting the generation of superoxide radicals. Notably, the Co_0.50La_0.50-MOF-74-4eq sample demonstrates exceptional molecular oxygen utilization and epoxidation performance, achieving a cyclohexene conversion of 92.2% with a selectivity of 93.9% for 1,2-epoxycyclohexane at 40 °C within 1 hour. Furthermore, this catalyst exhibits broad applicability across different substrates. Density functional theory calculations, complemented by in situ analysis, confirm that molecular oxygen activation occurs at Co sites while suppressing the allylic oxidation pathway, thus favoring the conversion of cyclohexene to epoxides. This work elucidates how strategically tailoring the electronic properties around catalytic sites can dramatically influence catalytic behavior in heterogeneous catalysis, providing new insights for the rational design of advanced catalysts.