CO Oxidation Catalysts Based on the Complex Antimonates of La2O3–CoO–Sb2O5 System

Abstract

Single-phase samples of compounds occurring in La₂O₃–CoO–Sb₂O₅ system have been prepared by the thermal decomposition of nitrates, citrate method, and co-precipitation with hydrothermal treatment of precipitate followed by annealing. Their catalytic properties in CO oxidation reaction have been studied. It has been found that LaCo_1/3Sb_5/3O₆ catalyst with rosiaite structure obtained by co-precipitation method with hydrothermal treatment of precipitate followed by annealing showed the highest activity at low temperatures and stability in cyclic testing. This catalyst provides 90% conversion of CO at 265°C. The surface of LaCo_1/3Sb_5/3O₆ has been studied by XPS, TPD-O₂ (temperature-programmed desorption of oxygen), and IR spectroscopy. It has been shown that Langmuir–Hinshelwood model is the most probable mechanism of catalytic CO oxidation, which is accompanied by redox processes Co³⁺ ↔ Co²⁺ and Sb³⁺ ↔ Sb⁵⁺ with participation of surface-active forms of oxygen and vacancies. Antimony ions in this process play role of electron donor, whose increased concentration favors to the acceleration of adsorption processes and formation of active oxygen forms on the surface. The lack of sample surface contamination has been found during catalysis, which excludes the need of its regeneration.