基于Cu-Ce复合氧化物的低浓度CH_(4)催化燃烧性能及微观机理

Performance and mechanism of low-concentration CH_(4) catalytic combustion based on composite oxides of Cu-Ce

我国每年通过乏风瓦斯排放大量CH_(4),造成严重的大气环境污染。催化燃烧法因其工作温度低、效率高,被认为是去除甲烷的有效途径之一。采用溶胶凝胶法制备了CuO-CeO_(2)、CuO和CeO_(2)三种催化剂,考察CH_(4)在(1%CH_(4),78%N_(2)和21%O_(2))气氛下的催化燃烧活性,并利用XRD、XPS、H_(2)-TPR、O_(2)-TPD等技术对催化剂的物理结构和表面性质进行表征。结果表明,Ce离子不但促进Cu物种在催化剂表面高度分散,并且其三价(Ce^(3+))和四价(Ce^(4+))之间转换提高了催化剂储放氧能力,有利于CuO-CeO_(2)提高催化剂活性。通过催化剂活性评价,得出3种催化剂的活性顺序为CuO-CeO_(2)>CuO>CeO_(2),再对活性最高的CuO-CeO_(2)催化剂开展分压反应动力学研究,确定甲烷在不同氧气/甲烷分压比下的反应速率,表明吸附的CH_(4)与吸附的O_(2)发生反应,CH_(4)在催化剂表面的氧化反应遵循L-H机理。基于原位红外光谱分析,提出了甲烷在CuO-CeO_(2)催化剂上的微观反应机理:CH_(4)吸附在CuO-CeO_(2)表面,再与CuO-CeO_(2)反应生成中间产物甲氧基物质(Cu-OCH_(3))和甲酸盐物质(Cu-OOCH),最后中间产物分解生成CO_(2)和H_(2)O,以达到完全氧化反应的目的。

A large quantity of CH_(4) is discharged from exhaust gas in China every year,which causes serious environmental pollution of atmosphere.Catalytic combustion is considered as one of the most effective ways to remove methane due to its low operating temperature and high efficiency.Herein,three catalysts,CuO-CeO_(2),CuO and CeO_(2),were prepared by sol-gel method to investigate the catalytic combustion activity of CH_(4) under(1%CH_(4),78% N_(2) and 21% O_(2))atmosphere.The physical structure and surface properties were characterized using XRD,XPS,H_(2)-TPR and O_(2)-TPD techniques,etc.The results show that Ce ions not only promote the dispersion of Cu on the catalyst surface,but also the conversion between trivalent(Ce^(3+))and tetravalent(Ce^(4+))improves the oxygen storage and release capacity of the catalyst,which is beneficial for CuO-CeO_(2) to improve the catalyst activity.The evaluation of catalyst activity provides evidence that the activity order of the three catalysts follows the order CuO-CeO_(2)>CuO>CeO_(2).Then,the most active CuO-CeO_(2) catalyst is employed to further investigate kinetic partial pressure experiment and reaction mechanism to determine the reaction rate of methane at different oxygen/methane partial pressure ratios.The results indicate that the reaction follows the L-H mechanism,that is,the adsorbed CH_(4) reacts with the adsorbed O_(2).Based on in-situ infrared spectra analysis,the microscopic reaction mechanism of CH_(4) over CuO-CeO_(2) catalyst is proposed:CH_(4) is firstly adsorbed on the surface of CuO-CeO_(2) and then reacts with CuO-CeO_(2) to produce intermediate products methoxy substance(Cu-OCH_(3))and formate substance(Cu-OOCH).Finally,the intermediate products are decomposed into CO_(2) and H_(2)O to achieve the purpose of the complete oxidation.