Molecular adaptability and reactivity in Ni6(SR)12-catalyzed adipic acid synthesis

Abstract

Constructing the active sites of a heterogeneous catalyst, controlling the accessibility of molecules to active sites and ultimately tailoring its catalytic property are of utmost significance yet highly challenging. Herein, we report two systems of atomically precise cluster catalysts for the cyclohexanone electrooxidation reaction, which correspond to 2-phenylethanethiol-protected Ni₆(SC₂H₄Ph)₁₂ and 1-dodecanethiol-protected Ni₆(SC₁₂H₂₅)₁₂. The two clusters are identified to have similar metal active cores while their distinct surrounding environments access to the metal cores are capable of discriminating between water and cyclohexanone, exhibiting substantially influences on their activity and selectivity. Our studies reveal that water molecules are preferably adsorbed onto the surface of the Ni₆(SC₁₂H₂₅)₁₂, thereby pushing the cyclohexanone molecule away from the metal core, which favors the oxygen evolution reaction on the Ni₆(SC₁₂H₂₅)₁₂ catalyst. In contrast, the cyclohexanone is adaptively pulled toward the Ni core by the 2-phenylethanethiol ligands of Ni₆(SC₂H₄Ph)₁₂, in which the C=O group of the cyclohexanone can approach, adsorb and convert over the Ni sites and 2-phenylethanethiol ligands have stronger electron interactions with Ni core facilitating the cyclohexanone oxidation reaction on the Ni₆(SC₂H₄Ph)₁₂ catalyst and hence achieving high faradaic efficiency and high yield for adipic acid. This study challenges the conventional heterogeneous catalysts without atomic-precision structure and instead couples the complementary roles of the inner and outer environments of the cluster catalysts to tailor their catalytic properties.