Selective and scaled-up continuous flow synthesis of manganese oxide nanocatalysts for single electron transfer reactions

Abstract

The application of high-quality nanomaterials in industrial products and processes is somewhat hindered by their actual market availability at a large scale, mostly due to preparation methods which can be hardly scalable for cost, reproducibility, sustainability or complexity issues. Herein, the application of the Continuous Flow Hydrothermal Synthesis (CFHS) is presented to prepare various nano Mn oxides in supercritical water with common and low-cost precursors and additives, yielding an outstanding production rate of 1 Kg day−1. Since Mn oxidation state spans from MnII to MnVII, the implemented process generates, with exquisite selectivity and consistency, nanosized MnO, α-MnO2, β-MnO2, λ-MnO2, Mn2O3, Mn3O4 and LiMn2O4 oxides with reproducible characteristics of the obtained phase under controlled synthetic conditions. As a case study, all our MnOx nanomaterials were tested as catalyst precursors in the Single Electron Transfer (SET) oxidation of olefins with 1,3-dicarbonyl compounds, obtaining recyclable active materials whose respective activity depends on the particular oxide structure, therefore proving the importance of phase selectivity in the final application.