Surface-frustrated Lewis pairs are unique catalytic sites formed by the combination of Lewis acid and Lewis base sites locked in close proximity on the material's surface. These pairs are particularly effective in accelerating catalytic conversions due to their collective ability to simultaneously accept and donate electrons, thereby facilitating bond breaking and formation. The team synthesized a series of isomorphic B-site-substituted LaMn1−xCuxO3 perovskite catalysts. Notably, partial substitution of Mn(IV) with Cu(II) in LaMn1−xCuxO3 increases the proportion of Mn(III) sites and leads to the emergence of oxygen vacancies and surface hydroxyl groups. This oxygen non-stoichiometry provides the necessary redox-active Lewis acid (Mn(IV)/Mn(III)) and Lewis base (O(-II) and OH(-I)) sites for surface-frustrated Lewis pairs formation. Among all the catalysts, the LaMn0.9Cu0.1O3 delivered the highest photocatalytic activity, achieving an ethylene production rate of 1.1 mmol g–1 h–1 and ethane conversion of 4.9%.
To elucidate the reaction pathway and the role of surface-frustrated Lewis pairs in facilitating C–H activation, the researchers probed ethane adsorption behaviour and Mn–H bond formation using in situ diffuse reflectance infrared Fourier transform spectroscopy, solid-state magic-angle spinning proton nuclear magnetic resonance, and density functional theory modelling. In the first C–H activation stage, a hydrogen from ethane bonds to a Lewis base oxygen or hydroxide site, forming Mn–OH or Mn–OH2 (pictured). Simultaneously, Mn–C2H5 forms at the Lewis acid sites. During the second step, a β-hydrogen of the anchored ethyl group is further activated by a Mn site to generate Mn–H species, followed by ethylene desorption and regeneration of the active sites. Under illumination, photogenerated electrons and holes are assumed to localize at the Lewis acid and Lewis base sites, respectively. This localization enhances the interaction between reactants and active sites, thereby minimizing the activation barriers. Additionally, as in other photothermal processes, local heat caused by irradiation further accelerates the reaction. This study provides a compelling demonstration of the applicability of the surface-frustrated Lewis pairs engineering strategy in developing efficient photocatalysts for activating stable molecules.
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