Dynamic Pt-OH-•H2O-Ag Species Mediate Synergetic Electron and Proton Transfer for Catalytic Hydride Reduction of 4-Nitrophenol at Confined Nanoscale Interface

Abstract

The nature of interfacial state and/or bonding at heterogeneous nanoscale surface of bimetals remains elusive. For very classical probe reaction of catalytic hydride catalytic reduction of –NO2 to NH2 (herein reduction of 4-NP to 4-AP as an example), three abnormal experimental phenomena cannot be elucidated as such: 1) the hydrogen source of final product of 4-AP is originated from water solvent, rather than NaBH4 reducer; 2) reverse electron transfer between bimetals was observed, which is resisted to the normal thermaldynamic law; 3) even in the absence of any metals, for example just using carbon nanodots as supports, the reaction occurs. These observations indicates that the reduction of –NO2 groups did not follow the classical metal-centered electron and hydride transfer mechanism, i.e., Langmuir-Hinshelwood (L-H) mechanism. We herein provide strong evidence that, the catalytic hydride reduction of 4-NP to 4-AP is though a completely new surface hydrous hydroxyl specie mediated concerted electron and proton transfer process, wherein owing to the space overlapping of p orbitals in hydrous hydroxyl intermediate, an ensemble of interface states are dynamically formed, which could be alternative channels for concerted electron and proton transfer. The main role of second metal of Pt is to regulate the density of surface hydrous hydroxyl intermediate and its interactive strength with metals. This new mechanism not only answers all the abnormal experimental observations above mentioned, but also provide some new insights to water and/or hydroxyl group promoted reaction involved the activation of small molecules (CO2, CO, N2, H2O etc.) in areas of electrochemistry, energy storage and metalloenzyme catalysis.