Ordered single active sites for cascade hydrogenation and hydroformylation reactions

Metal single-atom catalysts offer improved activity and selectivity due to their unique electronic and coordination properties compared with bulk metals. However, many single-atom catalysts suffer from randomly dispersed active sites and limited electron-donating ability due to bonding with electronegative elements or less reactive metals. Here we demonstrate that Mg-rich intermetallic Mg₂₉TM₄ (TM = Pd, Rh, Ir, Pt) nanocatalysts overcome these limitations. These materials feature periodically dispersed, electron-rich single-atom sites of noble metals within a uniform chemical environment. Mg₂₉TM₄ exhibits high activity and selectivity in C₂H₂ semihydrogenation (Mg₂₉Pd₄) and olefin hydroformylation (Mg₂₉Rh₄), with Mg₂₉Rh₄ achieving high regioselectivity for branched aldehydes (branched:linear > 200:1). Kinetic and density functional theory studies suggest that the Mg–TM ensemble enables precise control over carbon–carbon multiple bond adsorption and activation, enhancing both activity and selectivity. Furthermore, the ternary Mg₂₉Pd_1.3Rh_2.7 catalyst, with its synergistic Mg–Pd and Mg–Rh dual single-atom sites, efficiently catalyses a cascade reaction involving phenylacetylene hydrogenation followed by hydroformylation.