Facet-Dependent Oxygen Mobility and Reaction Pathways for Oxidative Dehydrogenation of 1-Butene over Bi2MoO6

The crystal facet effect is a critical factor for catalytic reactions on metal oxides due to the different atomic arrangements and physicochemical properties of diverse facets. Based on a series of combined experimental and theoretical measurements, this work investigates facet-dependent oxygen mobility and reaction pathways for the oxidation dehydrogenation (ODH) of 1-butene to 1,3-butadiene on Bi 2 MoO 6, which exposes the {001} and {010} facets (BMO-001 and BMO-010). The results show that the oxygen mobility of BMO-001 overwhelmingly outperforms that of BMO-010, reflecting the better capacities for selective abstraction of H from 1-butene, oxygen replenishment, and bulk lattice oxygen migration. Density functional theory (DFT) calculations indicate that the rate-determining step on the {001} facet is the abstraction of the first H in 1-butene and the abstraction of the second H on the {010} facet. The existence of the [Bi 2 O 2 ] 2+ layer provides a favorable channel with a low-energy barrier for bulk lattice oxygen migration toward the {001} facet. Besides, complex side reactions occur on the {010} facet, including the nonselective oxidation of 1-butene, aromatization of 1-butene, and the generation of CO and subsequent formates. The total oxidation and decomposition of byproducts result in extra CO 2 formation pathways. Lattice and gaseous oxygen play different roles in the above reactions. The superior oxygen mobility contributes to the high 1,3-butadiene yield for BMO-001, while the extra CO 2 formation pathways lead to an abnormally high CO 2 yield for BMO-010. The generated aromatic coke and formates affect the catalytic stability of BMO-010. The facet-dependent oxygen mobility and reaction pathways result in a distinct catalytic performance for 1-butene ODH.