Multifunctional Yolk-shell PdAg@ZIF-8 For Selective Hydrogenation Of Nitrostyrene

Metal-Organic Frameworks(MOF),also named Porous Coordination Polymers(PCPs),have attracted widespread interests among researchers over the past two decades and become one of the fastest growing fields in chemistry and materials science.As a class of porous crystalline materials,MOF are periodic network structure formed by self-assembly of inorganic metal nodes(metal ions/metal clusters,also known as secondary construction units or SBUs)and organic ligands.MOF are porous,tailorable and have uniform pore size and high surface area.These characteristics make MOF a potential in broad applications in gas adsorption and separation,drug delivery,proton conductivity and sensing,especially in heterogeneous catalysis.Metal nanoparticles(MNPs)have attracted a lot of attention in the field of catalysis due to their excellent activity.However,because of the high surface energy of small MNPs,agglomeration is easy to occur in the catalytic process,resulting in the decline of activity.Therefore,it is an effective strategy to load MNPs on porous materials to maintain their high activity.MOF are the most ideal porous material to incorporate MNPs,which provides spatial limitation to prevent the agglomeration and growth of MNPs,and their nanopores can be used for the transportation of reaction substrates/products.These advantages lead to the rapid development of MNPs/MOF in the catalytic field.However,when MNPs are incorporated with MOF,the exposed active sites of MNPs decreases,resulting in the low atomic utilization rate,which has a negative effect on the catalytic activity of MNPs/MOF.Heterogeneous hydrogenation of nitroaromatics is of great importance in the production of the corresponding aniline derivatives.Particularly,chemoselective hydrogenation of nitroaromatics with other functional groups,such as C=C or C=O,is a class of important reactions in industry.The produced functionalized anilines are significant industrial intermediates for the synthesis of pharmaceuticals,polymers,herbicides,and fine chemicals.Traditional catalysts like tin,zinc and iron will produce some harmful chemical wastes in the reaction process,which is not friendly for the environment.Moreover,most transition metal catalysts cannot distinguish different functional groups,so it is very difficult to reduce the nitro group in the presence of functional groups such as C=C and C=O.In addition,hydrogen gas is usually used in the reaction as the hydrogen source,requiring high pressure or heating conditions to drive the reaction.The conditions are harsh and cause a large amount of energy consumption.Therefore,the synthesis of green,mild,efficient and chemically selective catalysts is highly needed.In order to alleviate the increasingly severe energy shortage,utilizing solar energy instead of heat in the organic transformations is a promising way.Here we fabricated the plasmoic catalyst yolk-shell PdAg@ZIF-8 by coating PdAg nanocages with porous ZIF-8 to effectively catalyze the NH3BH3-initiated selective hydrogenation of nitrostyrene at ambient temperature and pressure under visible light.The PdAg nanocages integrate the excellent local surface plasmon resonance(LSPR)properties of Ag with the high catalytic activity of Pd;the unique yolk-shell structure exposes abundant actives;ZIF-8 shell enriches the substrate and in site H2 released by NH3BH3,further protects the PdAg cores from aggregation.Thanks to the multifunctional synergy,the plasmonic catalyst,yolk-shell PdAg@ZIF-8 have achieved the 100%conversion of nitrostyrene in 20 min with 97.5%selectivity for aminostyrene.