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

The activity of a hopcalite-type catalyst for H2 and CO oxidation is compared with that of single-phase oxides CuO, Mn2O3 and CuMn2O4 (spinel) and a mixture of 1:1 CuO and Mn2O3 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, Mn2O3 and CuMn2O4) are very close to those of the physical mixture of CuO and Mn2O3, being much greater than the rates over the single-phase oxides. CuO, Mn2O3 and CuMn2O4 show a kinetic compensation behavior both in H2 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 Mn2O3 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–Mn2O3 mixture is assigned to a spillover effect.