Reaction Energy Landscape of Propane Oxidative Dehydrogenation on Liquid Boron Oxide-Germinated Catalytic Sites in the Presence of Dioxygen: An Orbitals-Driven Mechanistic Study.

Abstract

Recently, boron-based catalysts have gained significant attention for the oxidative dehydrogenation of propane into propene and ethene. In this study, we present an electronic-level understanding of propane oxidation via a triplet dioxygen molecule over liquid boron oxide motifs, including cyclic B-O-B sites (8-, 6-, and 4-membered rings) and edge B-OH and B-B sites. Our computations reveal that cyclic B-O-B and edge B-OH motifs exhibit higher activation barriers for C₃H₆ (55-71 kcal mol^-1) and C₂H₄ (80-95 kcal mol^-1) formation. In contrast, the B-B site requires the lowest barrier among all sites. Orbital analysis reveals that ³O₂ activation at cyclic B-O-B sites proceeds via an electron transfer from O(2p) orbital into the antibonding orbitals of ³O₂. Over edge B-OH sites, the σ(O-H) bonding orbital facilitates ³O₂ activation. At the B-B site, the σ(B-B) bonding orbital transfers an electron into the antibonding orbital of ³O₂. Furthermore, transfer of an electron from the σ(C-H) of C₃H₈ to another antibonding orbital of ³O₂, leading to the generation of C₃H₇ radical. C₂H₄ formation over the B-B site has the lowest barrier, arising from the least strained seven-membered ring and the simultaneous cleavage of σ(C-C) and σ(C-O) bonds. This study underscores the industrial potential of boron-based catalysts.