Ce–Fe–Mn ternary mixed-oxide catalysts for catalytic decomposition of ozone at ambient temperatures

Abstract

Ce-modified Mn–Fe mixed-oxide catalysts were prepared by a citric acid sol-gel method and characterized by X-ray diffraction, Raman, N2 adsorption-desorption, infrared spectra, H2 temperature-programmed reduction and thermogravimetric analyses. Their catalytic properties were investigated in ozone (O3) decomposition reaction. Results show that the small amount of rare earth metal Ce added during Mn–Fe (FM) mixed-oxide synthesis greatly improves the catalytic performance in O3 decomposition. Among the prepared catalysts, the C0.04(FM)0.96 mixed-oxide catalyst exhibits the highest catalytic activity and stability. The O3 conversion over C0.04(FM)0.96 is 98% after 24 h reaction at 25 °C under dry condition, and that over FM decreases to 90% after 16 h reaction. At 0 °C, the O3 conversion over C0.04(FM)0.96 is 95% after 7 h reaction under dry condition, and that over FM slows down to 70%. Under humid condition (RH = 65%), the O3 conversion over C0.04(FM)0.96 is 63% after 6.5 h reaction at 25 °C, while that over FM decreases to 55%. When Ce is doped into Mn–Fe mixed oxides, the small amount of Ce enters the crystal lattice of MnO2, and partial Fe is separated to form Fe2O3. This changes cause lattice distortion and increase defects and enable the as-synthesized Ce–Fe–Mn ternary mixed-oxide catalysts to acquire additional oxygen vacancies and increase their specific surface area, thereby increasing the number of reaction sites and enhancing the catalytic performance of the catalysts forO3 decomposition.