Tri-Coordinated Boron Species in Confined Boron Oxide Catalysts for Enhanced Low-Temperature Oxidative Dehydrogenation of Propane

Boron-based catalysts exhibit great potential for oxidative dehydrogenation of propane (ODHP) to produce olefins. The straightforward synthesis of confined boron-based catalysts commonly using H₃BO₃ is intractable because of its abundant hydroxyl groups easily interacting with the supports in a spatially nonselective manner. Herein, we managed to construct a confined BO_x@SiO₂ catalyst showing an impressive low-temperature (400 °C) activity. This catalyst was prepared via the encapsulation of BN nanosheets by SiO₂ shell and subsequent oxidization steps. The in situ generated boron-oxygen species were anchored to silica shells via B─O─Si and hydrogen bonds. BO_x@SiO₂ exhibited a unique catalytic behavior of propane conversion uprush, increasing from 5.3% at 410 °C to 28.4% at 424.6 °C for ODHP reaction. That was attributed to the efficient activation of propane triggered by the newly formed tri-coordinated B─OH (B[3]^a and B[3]^b) active sites from the dispersion of molten BO_x species in confined SiO₂. Ab initio molecular dynamics (AIMD) simulations revealed that in the confined structure, the bond angles of O─B─O and B─O─B and system disorder of BO_x species increased significantly in molten state, favoring the dispersion of BO_x species and formation of B─OH groups, which drove the uprush of propane conversion.