A spillover approach to oxidation catalysis over copper and manganese mixed oxides

Abstract The activity of a hopcalite-type catalyst for H 2 and CO oxidation is compared with that of single-phase oxides CuO, Mn 2 O 3 and CuMn 2 O 4 (spinel) and a mixture of 1:1 CuO and Mn 2 O 3 in order to elucidate the effects that are responsible for the high catalytic activity of the former. The reaction rates over the hopcalite catalyst calcined at 550°C (a mixture of CuO, Mn 2 O 3 and CuMn 2 O 4 ) are very close to those of the physical mixture of CuO and Mn 2 O 3 , being much greater than the rates over the single-phase oxides. CuO, Mn 2 O 3 and CuMn 2 O 4 show a kinetic compensation behavior both in H 2 and CO oxidation. By taking into account the activation energies and the reducibility measured by TPR it was concluded that the oxidation reactions over CuO follow a redox mechanism using lattice oxygen, while over Mn 2 O 3 the mechanism is associative involving adsorbed oxygen species. Based on the TPR and kinetic results, the synergy between copper and manganese oxides in hopcalite and in the CuO–Mn 2 O 3 mixture is assigned to a spillover effect.