Thermal behaviour and structural variations of Mg-doped Cu-Mn mixed oxides and the catalytic activity of the thermal products in H₂O₂-decomposition

Abstract

Thermal decomposition of mixed copper and manganese carbonates in molar ratios 1:1 and 1:0.5 with respect to CuO: MnO₂ doped with, 2.5 and 5 wt.% Mg²⁺ has been studied. The thermal produces obtained at different temperatures have been characterized by X-ray diffraction analysis. The catalytic activity of the thermal products has been tested in H₂O₂decomposition. Calcination of mixtures at 200°C produces three crystalline phase CuO, Cu₂(NO₃)(OH)₃ and unaffected MnCO₃. The increase in temperature of treatment leads to the formation of manganese oxide which in turn reacts with CuO forming spinel CuMn₂O₄. The incorporated magnesium in the spinel structure occupies the octahedral coordinated sites [Cu<img src='http://www.niscair.res.in/jinfo/equation23.gif' border=0>Mn<img src='http://www.niscair.res.in/jinfo/equation24.gif' border=0>(Cu<img src='http://www.niscair.res.in/jinfo/equation24.gif' border=0>Mg<img src='http://www.niscair.res.in/jinfo/equation24.gif' border=0>Mn<img src='http://www.niscair.res.in/jinfo/equation26.gif' border=0>)O₄]. Catalytic activity of the undoped samples incre ses with increase in the calcination te perature up to 500°C and at 800°C it decreases. The doping wit magnesium ions shows slight change in activity for catalysts calcined at 200°C and 500°C, while conside rable increase in activity is detected for catalysts calcined at 800°C. This may be attributed to lattice inve rsion defects and distortions of the form ed spinel besides CuO present with other oxides.