Preferential dissolution of copper from Cu-Mn oxides in strong acid medium : effect of the starting binary oxide to get new efficient copper doped MnO2 catalysts in toluene oxidation

This work investigated the concept of preferential dissolution of copper in HNO3 10 M at 20 °C from two starting Cu-Mn oxides to acquire novel copper doped MnO2 like polymorphs. On purpose two starting Cu-Mn oxides were tested: a nanocristalline CuMn2O4 spinel phase with a SSA of 47 m2/g and a weak amorphous Cu-Mn oxide with a Mn/Cu atomic ratio of 4.8 (SSA: 166 m2/g). The physico-chemical properties of the final copper doped MnO2 like oxides were discussed in terms of the nature of the starting oxides and of the operating conditions applied for the acid treatment. Finally, these new copper doped γ/ε MnO2 like oxides were assessed in toluene oxidation and their catalytic performances were compared with those of α-MnO2 and ε-MnO2 catalysts. The copper doped MnO2 obtained from the weak amorphous Cu-Mn oxide exhibited the highest activity in terms of T50(CO2). This highest activity was related to a high density of Cu-O-Mn interactions at the outermost layers of the catalyst as assessed by ToF-SIMS results