Hot Electrons, Hot Holes, or Both? Tandem Synthesis of Imines Driven by the Plasmonic Excitation in Au/CeO2 Nanorods.

Ivo F Teixeira,Rafael S Geonmonond,Jhon Quiroz,Mauricio S Homsi,Yung-Kang Peng,Ingrid F Silva,Pedro H C Camargo,Guilherme F S R Rocha

doi:10.3390/nano10081530

Abstract

Solar-to-chemical conversion via photocatalysis is of paramount importance for a sustainable future. Thus, investigating the synergistic effects promoted by light in photocatalytic reactions is crucial. The tandem oxidative coupling of alcohols and amines is an attractive route to synthesize imines. Here, we unravel the performance and underlying reaction pathway in the visible-light-driven tandem oxidative coupling of benzyl alcohol and aniline employing Au/CeO2 nanorods as catalysts. We propose an alternative reaction pathway for this transformation that leads to improved efficiencies relative to individual CeO2 nanorods, in which the localized surface plasmon resonance (LSPR) excitation in Au nanoparticles (NPs) plays an important role. Our data suggests a synergism between the hot electrons and holes generated from the LSPR excitation in Au NPs. While the oxygen vacancies in CeO2 nanorods trap the hot electrons and facilitate their transfer to adsorbed O2 at surface vacancy sites, the hot holes in the Au NPs facilitate the α-H abstraction from the adsorbed benzyl alcohol, evolving into benzaldehyde, which then couples with aniline in the next step to yield the corresponding imine. Finally, cerium-coordinated superoxide species abstract hydrogen from the Au surface, regenerating the catalyst surface.

Highlights

Photocatalysis can initiate or accelerate chemical reactions by the light–matter interaction, which can simultaneously solve the problems about solar energy conversion and storage [1]
We propose an alternative reaction pathway for this transformation that leads to improved efficiencies relative to individual CeO2 nanorods, in which the localized surface plasmon resonance (LSPR) excitation in Au NPs played an important role
The Raman spectrum of Au/CeO2 differed from the spectrum of CeO2 nanorods mainly by the main peak at 450–460 cm−1 assigned to oxygen ions vibrational mode in the

Summary

Introduction

Photocatalysis can initiate or accelerate chemical reactions by the light–matter interaction, which can simultaneously solve the problems about solar energy conversion and storage [1]. It has been shown that the nonradiative decay following localized surface plasmon resonance (LSPR) excitation in plasmonic metals leads to hot electrons and holes, that can participate in the electronic or vibrational activation of species close to the surface [9,10]. This provides sufficient energy to initiate, accelerate, and/or control molecular transformations [9,10]. Our data suggests a synergism between the hot electrons and holes generated from the LSPR excitation in Au NPs, which acted in combination with the oxygen vacancies in the CeO2 to improve catalytic activities

Au Nanoparticles Synthesis

Catalyst Characterization

Photocatalytic Tests

XPS Analysis

Results and Discussion