It has been widely accepted that decreasing the pH value could enhance the reactivity of 4-Nitrophenol (4-NP) reduction accompanied with the pillage of H2, but excess hydrogen generation is wasteful and easy to lead to safety problems. Herein, we show that, contrast to previously reported results, interfacial adsorbed hydroxyl significantly promotes reduction of 4-NP using Ag-based nanoparticles (NPs) confined in dendritic mesoporous silica nanospheres (Ag@DMSNs) as a model catalyst at medium concentration of sodium hydroxide (NaOH). We provide strong evidences that adsorptive 4-NP and hydroxyl could spatially interact to form an intermediate state through p-p overlapping of O atoms at nanoscale interface of Ag NPs, which leads to electron redistribution and accelerates N=O bonds cleavage, and consequently accelerates the reduction of 4-NP. The findings of this work demonstrate that improving the catalytic performance can be holistically achieved through manipulating the weak interactions between reactant and enthetic species on the molecule level. Introduction: 4-Aminophenol (4-AP), the reduction product of 4-NP, is a potent intermediate for the manufacture of pharmaceuticals and dyes. 1 However, without the catalyst, the hydrogenation of 4-NP to 4-AP by NaBH4 is kinetically restricted due to kinetic barriers resulting from the large potential difference between 4-NP and BH4-. 2 In recent years, noble metal nanoparticles (MNPs) have been discovered to exhibit high catalytic activity for selective reduction of 4-NP in the presence of NaBH4, such as Ag NPs, 3 Au NPs, 4 Pd NPs, 5 and Pt NPs. 6 Among these MNPs catalysts, Ag-based catalysts are distinctive (easy preparation, relatively low cost, less toxicity, high activity and good stability) and have been extensively utilized for 4-NP reduction. 7 However, it should be noted that MNPs catalysts are susceptible to suffer from aggregating due to the Van der Waals forces and high surface free energy. 8 For 4-NP reduction on Ag-based catalysts, the formation of large metal particles largely affects the catalytic activity and reusable performance. Accordingly, silver nanoparticles anchored through organic (such as polymers and DNA) 9 or inorganic (such as glasses, metal oxides and zeolites) 10 templates have been proposed to address the above issues. Among them, dendritic mesoporous silica nanospheres (DMSNs) composed of cage-like spherical nanopores have been confirmed as a unique confinement matrix for the encapsulation of MNPs and enable their application in catalysis. 11 The catalytic performance of MNPs catalysts strongly depends on their microstructure (catalyst composition, exposed crystal face, defect sits, adsorbed species, etc.) and reaction microenvironment (pressure, solvent, pH etc.). Although the reduction of 4-NP is intensively studied as a model reaction, the reaction mechanism is not yet fully comprehended. It is widely accepted that the reduction of 4-NP follows a multistep reduction process and the 4-hydroxylaminophenol (Hx) is a relative stable inte...
