Surface In Situ Doping Modification over Mn₂O₃ for Toluene and Propene Catalytic Oxidation: The Effect of Isolated...

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 Cu^δ+ was predominantly inserted into the mezzanine of the [MnO₆]^δ- layers in MnO₂ instead of K⁺, leading to slight electron transfer from Cu^δ+ 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 Cu^δ+ 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.