Highly efficient cobalt-modified hopcalite catalysts prepared through crednerite–spinel transformation†

The work presents a study and comparison of the catalytic properties of hopcalite catalysts composed of copper–manganese and copper–cobalt–manganese spinel particles in the low-temperature CO oxidation reaction. The cubic spinel structure was formed immediately under reaction conditions through the transformation of hydrothermally prepared crednerite CuMn(Co)O₂ particles. Both the initial crednerite-type and the resultant spinel-type particles (Cu, Mn, Co)₃O₄ exhibited a lamellar morphology and a uniform distribution of elements throughout their bulk and surface. It was found that the modification of the copper–manganese oxide with cobalt resulted in increased particle dispersion and a significant distortion of the crednerite crystal lattice. As a result, this modification reduced the temperature required for the crednerite-to-spinel transformation to 250 °C, whereas the unmodified catalyst is transformed after heating to 350–400 °C only. Furthermore, it was demonstrated that during the CO oxidation at room temperature, the modified spinel particles (Cu, Mn, Co)₃O₄ exhibited a specific catalytic activity ∼3.5 times greater than that of the copper–manganese system. This enhancement is associated with the stabilization of a more oxidized surface state for the modified spinel particles, which may involve an increased contribution of Co³⁺ and Mn⁴⁺ surface species, as well as an enhancement in the overall lattice oxygen mobility.