Effect of the Calcination Temperature and Composition of the MnOx–ZrO2 System on Its Structure and Catalytic Properties in a Reaction of Carbon Monoxide Oxidation

Аннотация

The effect of the calcination temperature and composition of the MnO_x–ZrO₂ system on its structural characteristics and catalytic properties in the reaction of CO oxidation was studied. According to X-ray diffraction analysis and H₂ thermo-programmed reduction data, an increase in the calcination temperature of Mn_0.12Zr_0.88O₂ from 450 to 900°C caused a structural transformation of the system accompanied by the disintegration of solid solution with the release of manganese ions from the structure of ZrO₂ and the formation of, initially, highly dispersed MnO_x particles and then a crystallized phase of Mn₃O₄. The dependence of the catalytic activity of MnO_x–ZrO₂ in the reaction of CO oxidation on the calcination temperature takes an extreme form. A maximum activity was observed after heat treatment at 650–700°C, i.e., at limiting temperatures for the occurrence of a solid solution of manganese ions in the cubic modification of ZrO₂. If the manganese content was higher than that in the sample of Mn_0.4Zr_0.6O₂, the phase composition of the system changed: the solid solution phase was supplemented with Mn₂O₃ and β-Mn₃O₄ phases. The samples of Mn_0.4Zr_0.6O₂–Mn_0.6Zr_0.4O₂ exhibited a maximum catalytic activity; this was likely due to the presence of the highly dispersed MnO_x particles, which were not the solid solution constituents, on their surface in addition to an increase in the dispersity of the solid solution.