Electrostatic Interactions Induced Ligand Re-orientation for Catalytic Performance Improvement of Metal Nanoclusters

Abstract

Catalytic activity and durability represent a long-lasting dilemma in catalytic applications of metal nanoparticles. Herein, we report a dehydration-rehydration strategy for immobilizing metal nanoclusters (NCs, <3 nm nanoparticles) on MgAl layered double hydroxides (MgAl-LDHs) for simultaneously promoting their catalytic activity and durability. This approach relies on the reversible dehydration-rehydration process of MgAl-LDHs, in which anionic Au₂₅(p-MBA)₁₈ NCs (p-MBA = para-mercaptobenzoic acid) can be effectively tethered on positively charged MgAl hydroxide layers to yield Au₂₅/LDH composites. The strong electrostatic interactions of 2D MgAl hydroxide layers with carboxylate groups of p-MBA ligands are effective in re-orientating the p-MBA ligands on cluster surface, exposing more active Au sites for catalytic reactions. Such enhanced active Au site accessibility is conducive to improving catalytic activity of Au₂₅/LDH composites toward selective reduction of 4-nitrophenol to 4-aminophenol. Au₂₅/LDH composites achieve complete conversion of 4-nitrophenol within 180 s with a rate constant of 0.0183 s^–1, while their catalytic activity remains uncompromised within ten catalytic cycles. This study not only provides a simple yet effective strategy for stabilizing and activating metal NCs for catalytic applications, but also affords an alternative mechanism for engineering the catalytic activity of metal NCs via ligand re-orientation.

Keywords

Metal nanoclusters / Layered double hydroxides / Green catalysis / Surface engineering / Ligand re-orientation / Sustainable chemistry / Heterogeneous catalysis / Electrostatic interactions

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