Abstract:

Volatile organic compounds (VOCs) such as toluene in the atmosphere are known to be potentially harmful to the environment and to human health, and catalytic combustion is one of the effective methods to remove the VOCs. In this work, rod-like copper-manganese mixed oxides with high specific areas were produced from copper-manganese mixed oxide particles by hydrothermal treatment with sodium hydroxide. The catalytic activity and deactivation of toluene combustion on these materials were subsequently studied. It was found that the catalytic combustion activity was greatly affected by the calcination temperature of the oxide. A sample calcined at 500 ℃ with a Brunauer-Emmett-Teller (BET) surface area of 221 m²·g^-1 exhibited an activity very close to that of noble metal catalysts, enabling the complete catalytic combustion of toluene at 210 ℃. After running at 250 ℃ for 60 h, the toluene conversion droped from an initial value of 100% to 83%. X-ray photoelectron spectroscopy (XPS) and hydrogen temperature-programmed reduction (H₂-TPR) showed that the relative proportions of Mn⁴⁺ and Mn³⁺ in the used catalyst decreased from 40.4% and 55.0% to 29.9% and 50.0%, respectively, while the relative proportion of Mn²⁺ increased from 4.60% to 20.6%. In addition, the amount of surface-adsorbed oxygen decreased from 34.8% to 29.2%, indicating that the catalytic activity is closely related with surface-adsorbed oxygen and high-valance Mn species. The H₂-TPR peaks associated with copper oxide and manganese oxide transitioned from 248 and 311 ℃ to 268 and 333 ℃, respectively, illustrating that the deactivation resulted from a loss of redox properties. These results will be useful in further developing highly efficient, stable materials for the catalytic removal of VOCs in the atmosphere.

Key words: Copper manganese oxide, Catalyst deactivation, Catalytic combustion, Hydrothermal treatment, Toluene