在类棒状铜锰复合氧化物上甲苯的催化燃烧活性及其失活

大气中的甲苯等挥发性有机物对环境和人体健康具有很大的危害。催化燃烧法是去除大气中挥发性有机物的一种有效方法。本文利用共沉淀法制备的铜锰复合金属氧化物经氢氧化钠水热处理后，获得了高比表面积的类棒状铜锰复合氧化物材料，并考察了其对甲苯的催化燃烧的活性和失活原因。研究表明，样品的后处理温度对甲苯催化燃烧活性影响很大，经500 ℃焙烧的样品比表面积高达221 m²·g^-1，在210 ℃可以实现甲苯的完全燃烧，其催化活性与贵金属催化剂Pd相当。所研制的类棒状铜锰复合氧化物在250 ℃时，运行60 h后甲苯转化率从最初的100%降至83%，通过对新鲜催化剂和反应后催化剂进行X射线光电子能谱分析(XPS)和氢气程序升温还原(H₂-TPR)的分析，发现失活后样品上Mn⁴⁺和Mn³⁺的含量分别由40.4%、55.0%降为29.9%、50.0%，同时Mn²⁺的含量分别由4.60%升高为20.6%，表面氧由34.8%降低到29.2%，表明催化剂的活性位与表面氧和高价态的锰密切相关；另一方面，失活后样品的H₂-TPR上氧化铜的还原峰温度从248 ℃上升至268 ℃，氧化锰的还原峰从311 ℃上升至333 ℃，表明该高活性催化剂的失活可能与其随着反应的进行变得更难还原相关。本研究结果将有助于在大气污染控制中，进一步设计出高活性高稳定性净化大气中挥发性有机物的低温催化燃烧催化剂。

Catalytic Activity and Deactivation of Toluene Combustion on Rod-Like Copper-Manganese Mixed Oxides

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.