The role of lattice oxygen on the activity of manganese oxides towards the oxidation of volatile organic compounds

• Published in: Applied catalysis. B, Environmental Environmental, 2010-08, Vol.99 (1-2), p.353-363
• Main Authors: Santos, V.P., Pereira, M.F.R., Órfão, J.J.M., Figueiredo, J.L.
• Format: Article
• Language: English
• Subjects: Catalysis; Catalysts; Chemistry; Cryptomelane; Ethanol; Ethyl acetate; Ethyl alcohol; Exact sciences and technology; General and physical chemistry; Lattices; Manganese oxides; Oxidation; Surface physical chemistry; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Toluene; Volatile organic compound; Volatile organic compounds
• ISSN: 0926-3373; 1873-3883
• DOI: 10.1016/j.apcatb.2010.07.007

T50 (open symbols) and T90 (filled symbols) determined for ethanol and toluene oxidation as a function of the amount of CO2 obtained in the reactions without oxygen in the feed. [Display omitted] ▶ Manganese oxides are very active for the total oxidation of VOC. ▶ The catalyst that contains cryptomelane and Mn3O4 presents the best performance. ▶ There is a correlation between the reducibility and the activity of Mn oxides. ▶ TPSR and tests without O2 show that lattice oxygen is involved in the mechanism. A series of manganese oxides differing in the structure, composition, average manganese oxidation state and specific surface area have been used in the total oxidation of volatile organic compounds (VOC). Ethanol, ethyl acetate and toluene were chosen as models of VOC. Among the manganese oxides tested, cryptomelane (KMn8O16) was found to be very active in the oxidation of VOC. The performance of cryptomelane was significantly affected by the presence of other phases, namely, Mn2O3 and Mn3O4. Temperature-programmed experiments combined with X-ray photoelectron spectroscopy (XPS) show that the mobility and reactivity of the oxygen species were significantly affected, explaining the catalytic performances of those samples. Mn3O4 improves the catalytic performance due to the increase of the reactivity and mobility of lattice oxygen, while Mn2O3 has the opposite effect. These results show that there is a correlation between the redox properties and the catalytic performance of the manganese oxides. Temperature-programmed surface reactions (TPSR) after adsorption of toluene or ethanol, in addition to reactions performed without oxygen in the feed, show that lattice oxygen is involved in the VOC oxidation mechanism. The conversion level was found to be influenced by the type of VOC, the reactivity into CO2 increasing in the following order: Toluene