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

The effect of the calcination temperature and composition of the MnO x –ZrO 2 system on its structural characteristics and catalytic properties in the reaction of CO oxidation was studied. According to X-ray diffraction analysis and H 2 thermo-programmed reduction data, an increase in the calcination temperature of Mn 0.12 Zr 0.88 O 2 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 ZrO 2 and the formation of, initially, highly dispersed MnO x particles and then a crystallized phase of Mn 3 O 4 . The dependence of the catalytic activity of MnO x –ZrO 2 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 ZrO 2 . If the manganese content was higher than that in the sample of Mn 0.4 Zr 0.6 O 2 , the phase composition of the system changed: the solid solution phase was supplemented with Mn 2 O 3 and β-Mn 3 O 4 phases. The samples of Mn 0.4 Zr 0.6 O 2 –Mn 0.6 Zr 0.4 O 2 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.