Surface In Situ Doping Modification over Mn₂O₃ for Toluene and Propene Catalytic Oxidation: The Effect of Isolated Cu^δ+ Insertion into the Mezzanine of Surface MnO₂ Cladding

Heterocation insertion and substitution in tunnels and mezzanines of MnO2 present significant influences on the microchemical environment at the surfaces and interfaces. An innovative surface in situ doping modification method via Cu2+–H+/KMnO4 treatment was applied onto the Mn2O3 surface to provide Mn2O3@MnO2 nanospheres. Cu was stabilized into resulting MnO2 cladding substituting original K+ during a mild comproportionation reaction between Mn(VII) and Mn(III). The Cu25 (Cu(II): Mn(VII)atomic = 25%) catalyst shows significant promotion of the catalytic performance compared with bare Mn2O3 and Cu0 (without Cu involving). Isolated Cuδ+ was predominantly inserted into the mezzanine of the [MnO6]δ− layers in MnO2 instead of K+, leading to slight electron transfer from Cuδ+ to outermost Mn(4−ε)+ and a decrease of interlayer spacing as well as crystallinity. Such a configuration facilitates the formation of additional oxygen vacancies, promoting the redox ability and oxygen mobility at relatively low temperatures. The mechanistic study reveals that Cuδ+ in MnO2 cladding boosts the activation of toluene (methyl) to form benzoates and propene (methyl and double bonds) to form carboxylates, enhancing the chemical adsorption of reactants. Moreover, it also inhibits the unfavored accumulation of incomplete oxidized intermediates on the surface at high temperatures.