Published online by Cambridge University Press: 10 February 2011
Nonstoichiometric nickel manganite spinels NixMn3-x □3δ/4O4+δ, have been synthesised by calcination of mixed oxalates in air at 350°C. The variation of the electrical conductivity σ with partial pressure of O2 shows that these oxides are n-type semiconductors; σ also varies with the nickel content and has a maximum at x = 0.6. The intrinsic catalytic activity of these oxides for CO/CO2 conversion varies with nickel content and the most active catalyst is at x=0.6 where the conversion starts at room temperature. The variation of the catalytic activity and the electrical conductivity and the nickel amount are correlated. Apparent activation energies are very low (less than 20 kJ/mol) and remain the same for all these mixed oxides. Similarly, the reaction order with respect to O2 and CO does not depend on the nickel content (order/O2 ≈ 0; order/CO ≈ 0.6). A reaction mechanism involving formation of oxygen ions adsorbed and carbonate species is discussed.
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