Facet-regulated local coordination of oxygen species on MgO for efficient cycloaddition of CO2 with propylene oxide

Regulating the concentration of low-coordinated oxygen species on certain exposed crystal facets of oxides still remains a challenge. Herein, we developed a facile facet-engineering method to construct regulable ratios of (100), (110), and (111) facets on the MgO by modulating the surface curvature. As revealed by in situ CO2 diffused reflectance infrared Fourier transform spectroscopy and kinetic studies, it is found that MgO with a high density of active facets (i.e., [111] and [110] facets) exhibits ca. two times higher CO2 adsorption capacity. Based on the results of the density functional theory calculation, the activation of CO2 by MgO is enhanced with the increase in low-coordinated oxygen on active facets. Notably, the trapezoidal MgO with high-density active facets shows an increase in propylene epoxide conversion by ca. 33% without halogens, while maintaining a high propylene carbonate selectivity of 97.9%. This work will pave the way for the rational design of high-performance oxide catalysts by the facet-regulating strategy.