Promotion of Acetylene Semi-Hydrogenation by Oxide-Oxide Interactions in FeOX/TiO2 Catalysts

Abstract

Oxide catalysts have garnered significant attention in heterogeneous catalysis due to their excellent activity and cost-effectiveness. While metal-support interactions have been widely studied, the role of oxide-oxide interactions in tuning catalytic behavior remains underexplored. In this study, we developed a FeOX/TiO2 catalyst with a Fe3+/Fe2+ ratio of approximately 1:1 by depositing iron oxide onto TiO2 followed by hydrogen reduction. Compared to pure FeOX and physically mixed FeOX-TiO2, the FeOX/TiO2 catalyst demonstrated superior performance in the semi-hydrogenation of acetylene, achieving 100 % acetylene conversion and 93 % ethylene selectivity with excellent stability over 100 hours. Characterization results reveal that oxide-oxide interactions between FeOX and TiO2 significantly regulate the oxidation state of iron, promoting the formation of metastable FeOX species while inhibiting over-reduction to Fe0. In contrast, pure FeOX tends to form Fe0, which binds acetylene and ethylene too strongly, resulting in poor selectivity due to over-hydrogenation. DFT calculations show that hydrogen undergoes homolytic dissociation on pure Fe2O3 and FeOX, but heterolytic dissociation with a lower energy barrier is favored at oxygen vacancies and Fe sites on the FeOX/TiO2 interface. This facilitates the formation of active hydrogen species conducive to selective hydrogenation. Additionally, C2H4 desorption energy on FeOX/TiO2 is significantly lower than its further hydrogenatio, unlike on pure FeOX. In situ DRIFTS confirms π-bonded acetylene adsorption and the formation of OH groups during the reaction is positively correlated with the production of ethylene, verifying the critical role of H2 heterolytic dissociation. This work highlights the mechanistic importance of oxide–oxide interactions in modulating iron valence, hydrogen activation, and selectivity, offering new insights for designing high-performance oxide-based catalysts.