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

Abstract

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 1butene 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.

Facet-dependent catalysis of γ-Bi2MoO6 for selective oxidation of isobutene to methacrolein

“…420, 610 and 650 K. The former was attributed to the oxidation of partially reduced bismuth, the middle one was ascribed to the oxidation process of partially reduced molybdenum, and the latter was due to the combustion of carbon deposits. 48,49 Notably, the O 2 -consumption temperature relating to Bi/Mo species over Bi 2 MoO 6 -S (417 and 605 K) was lower than that of Bi 2 MoO 6 -F (427 and 611 K). Moreover, the peak area of O 2 -consumption on Bi 2 MoO 6 -S was 1.4 times higher than that on Bi 2 MoO 6 -F. The O 2 -consumption behaviour generally indicates the reactivity of oxygen species on Bi 2 MoO 6 samples, which was intimately correlated with the catalytic activities for the selective oxidation of isobutene.…”