Influence of the B3+ Cation Nature on the Properties of Cu B O2 Oxides (B=Mn, Co, Cr, Fe, and Ga) with a Delafossite/Crednerite Structure

Abstract

The paper presents an investigation into the physicochemical and catalytic properties of CuBO₂ oxides with a delafossite/crednerite-type structure, exploring the dependence on the nature of the B³⁺ cation (Mn³⁺, Co³⁺, Cr³⁺, Fe³⁺, and Ga³⁺). The catalytic properties in CO oxidation were examined in conjunction with structural data, surface composition, the distribution of surface metal states, and the reactivity of oxygen. The selection of synthesis conditions was tailored to yield crystallized CuBO₂ particles exhibiting either a delafossite or crednerite structure, depending on the nature of the B³⁺ cation nature. Thermal stability increases in the following order: CuMnO₂ < CuCrO₂ ≈ CuFeO₂ ≈ CuCoO₂ < CuGaO₂. Heating of all the studied mixed oxides in the CO + O₂ mixture to 250 °C did not cause changes in the phase composition and structural characteristics. The highest catalytic activity near room temperature was observed for CuMnO₂ and CuCrO₂. A correlation was established between the catalytic activity of CuBO₂ and the reactivity of surface oxygen, presumably attributed to the pronounced lability of the redox transitions between the Cu¹⁺/Cu²⁺ and Bⁿ⁺/B^m+ pairs. The transformation of the delafossite/crednerite into a spinel structure can cause both deactivation (B = Fe and Co) and significant catalytic activation (B = Mn and Cr) in low-temperature CO oxidation.