Ionic-Fence Effect in Au Nanoparticle-Loaded UiO-66 Metal-Organic Frameworks for Highly Chemoselective Hydrogenation

The chemoselective reaction are vital for fine chemicals, which requires economical and environmentally friendly catalysts. In order to improve the selectivity of multi-reaction competition, herein, we propose a novel ionic-fence strategy to synthesize heterogeneous catalyst for efficient hydrogenation. Practically, UIO-66 metal-organic frameworks (MOF) modified with pyridinium-linker has been constructed through post-synthetic chains with paired anion via quaternization and ion exchange to form ionic-fence MOF (IFMOF-Cl), which can manage the adsorption mode of nitro substrate, further confine the formation of metal nanoparticles with high dispersity. The optimal Au@IFMOF-Cl catalyst demonstrates satisfactory selectivity for hydrogenation of nitro group compared to acetylene group in 4-nitrophenylacetylene. Specifically, it owns a high yield of 4-aminophenylacetylene (~97 %) with ultra-high catalytic efficiency (3880 h^-1 TOF) and long stability, far superior to other catalysts without ionic fence effect. Adsorption experiments and density functional theory studies reveal that the incorporation of ionic fence could modulate the adsorption energy of nitro group, which is responsible for the high selectivity enhancement. Notably, this ionic-fence strategy exhibits comprehensive universality towards a wide range of substrates (23 kinds in total), providing a promising avenue for precisely engineering the internal microenvironments of catalysts to achieve highly selective synthesis of fine chemicals.