Europium-doped cryptomelane: Multi-pathway synthesis, characterization, and evaluation for the gas phase catalytic oxidation of ethanol

Abstract

Cryptomelanes (OMS-2) are synthesized by solvent-free and reflux methods and doped with Eu via co-precipitation and ion-exchange to investigate Eu’s effects on physical, chemical, and catalytic properties. The catalysts are characterized by XRD, SEM, TEM, N2 Adsorption, and TGA and evaluated for catalytic activity in the oxidation of ethanol. Eu-doping by co-precipitation generally improved catalytically favorable physical and chemical properties whereas Eu-doping by ion-exchange shows deleterious effects. The position of Eu in the structure seems to be the main factor in controlling catalytic activity with Eu3+→Mn3+ replacement in the solid-state co-precipitated type performing the best in the oxidation reaction (Ea =32.0 kJ/mol vs. 78.2 kJ/mol, SS-CP and control, respectively). This study demonstrates that Eu-doping affects the physical and catalytic properties of cryptomelane which provides an understanding of crystallization kinetics and helps guide further catalytic modification efforts.