Synthesis of Bi1.5CoSb1.5O7 with the Pyrochlore Structure under Hydrothermal Conditions and Its Catalytic Properties in the Reaction of CO Oxidation

Abstract

The boundaries of the existence of a solid solution with a pyrochlore structure in the Bi₂O₃–CoO–Sb₂O₅ system were found. A previously unknown ternary oxide Bi₃Co_2/3Sb_7/3O₁₁ was discovered, which belongs to the cubic KSbO₃ structure type (space group Pn\(\bar {3}\), a = 9.5801(1) Å, wR = 0.0132). The isothermal cross section of the system in the region CoO–Bi₃SbO₇–CoSb₂O₆–BiSbO₄ at 700°C was triangulated. It was shown that cobalt in the pyrochlore crystal lattice exists in the +2 oxidation state. By the example of the compound Bi_1.5CoSb_1.5O₇, a method was developed for the hydrothermal synthesis of pyrochlore both without and with microwave irradiation. Based on the data of X-ray powder diffraction analysis, local X-ray spectral microanalysis, scanning microscopy, and IR spectroscopy, a mechanism was proposed for the formation of the pyrochlore phase under hydrothermal conditions. Fine powders samples of Bi_1.5CoSb_1.5O₇ (coherent scattering region size 30 nm) were synthesized, and the prospects of their use as catalysts for CO oxidation were shown.