Stabilizing Oxidative Dehydrogenation Active Sites at High Temperature with Steam: ZnFe₂O₄‑Catalyzed Oxidative Dehydrogenation of 1‑Butene to 1,3-Butadiene

Dehydrogenation reactions are central for the production of functional molecules. Steam plays a pivotal role in ZnFe₂O₄-catalyzed 1-butene oxidative dehydrogenation (ODH). However, the essential effect of steam on this reaction is still unclear. Herein, we describe the structure–performance relationships of ZnFe₂O₄ in the presence/absence of steam by combined density functional theory and experimental studies. The catalytic performances of ZnFe₂O₄ under different reaction conditions were investigated. The ZnFe₂O₄(110) surface properties under reaction conditions and molecular reaction pathways were modeled. Free-energy profiles were calculated. We found that an oxygen-excess ZnFe₂O₄(110)–O termination, with an extra O atom bridging two Fe cations, is preferred under oxygen-rich conditions. However, both experimental and theoretical approaches indicate that this surface bicoordinated O is not stable at relatively high temperatures in the absence of steam, resulting in the reduction of surface Fe³⁺ cations to Fe²⁺ which are inactive in the 1-butene ODH reaction. It was found that steam interacts strongly with the ZnFe₂O₄(110)–O surface. Steam stabilizes the catalyst surface Fe³⁺ ions by converting bicoordinated O to more thermally stable hydroxyl groups. Surface hydroxyls are active sites for C–H bond cleavage in the 1-butene ODH reaction in the presence of steam. We propose that the role of steam elucidated here represents a general mode of steam influence in ODH reactions over oxide surfaces.