Manganese oxides supported on gold nanoparticles: new findings and current controversies for the role of gold

Abstract

We synthesized manganese oxides supported on gold nanoparticles (diameter <100 nm) by the reaction of KMnO4 with gold nanoparticles under hydrothermal conditions. In this green method Mn oxide is deposited on the gold nanoparticles. The compounds were characterized by scanning electron microscopy, energy-dispersive spectrometry, high-resolution transmission electron microscopy, X-ray diffraction, UV-Vis spectroscopy, Fourier transform infrared spectroscopy, and atomic absorption spectroscopy. In the next step, the water-oxidizing activities of these compounds in the presence of cerium(IV) ammonium nitrate as a non-oxo transfer oxidant were studied. The results show that these compounds are good catalysts toward water oxidation with a turnover frequency of 1.0 ± 0.1 (mmol O2/(mol Mn·s)). A comparison with other previously reported Mn oxides and important factors influencing the water-oxidizing activities of Mn oxides is also discussed.

In Situ Synthesis of Manganese Oxide as an Oxygen‐Evolving Catalyst: A New Strategy

“…On the other hand, Nature uses a manganese‐calcium oxide‐based cluster as an efficient oxygen‐evolving catalyst, [6] which is of great interest as a model for designing artificial oxygen‐evolving catalysts [7] . In using Mn oxides as water‐oxidizing catalysts, the challenges are finding the mechanism of OER at an atomic level, the rate‐determining step, improving the synthetic procedure for Mn oxide formation, understanding the mechanism of Mn‐oxide formation, finding the roles of Mn ions with different oxidation states (II‐VII) in the meanwhile of OER, the conversion of numerous Mn oxides over OER, detection of the active intermediate during OER, and the roles of Mn III in OER [8–25] …”

“…Different phases of Mn oxide were reported as efficient catalysts for OER [5] . Gold particles were reported to improve the activity of Mn oxides, [12] but what exactly the role of gold in OER by Mn oxide is, remains a challenging issue [13] …”