钙钛矿型催化剂催化燃烧VOCs的抗水蒸气性能研究

用柠檬酸溶胶-凝胶法制备了La0.8M0.2CoO(3M=Sr,Ce,Ba,Ca)4种钙钛矿型复合氧化物催化剂。通入相对湿度为70%的甲苯测试表明,相比较于没有水蒸气存在的情况,4种催化剂的催化活性都有所下降。同时还可发现,A位部分取代的离子不同,催化剂的催化活性下降程度不同,即抗水蒸气性能也不同。所制备的四种催化剂的抗水蒸气性能依次为La0.8Sr0.2CoO3>La0.8Ce0.2CoO3≈La0.8Ca0.2CoO3>La0.8Ba0.2CoO3,其ΔT50%分别为12℃、20℃、20℃和50℃左右,说明除La0.8Ba0.2CoO3外,其它3种对水蒸气具有一定的抗中毒性能。XRD、BET和SEM表征结果证实,水蒸气分子与甲苯分子竞争吸附占据催化剂表面部分活性位,使用于催化氧化甲苯的有效活性位相对减少;同时其与活性组分在高温下发生反应生成新物质,在催化剂表面形成一层致密的涂层,堵塞了原来的孔道结构,从而使催化剂比表面积减少而活性下降。

Water Vapor Resistance of Perovskite Catalysts for VOCs Catalytic Combustion

Four perovskite catalysts La0.8M0.2CoO3(M=Sr,Ce,Ba,Ca)were prepared by sol-gel method using citric acid as complex agent.Experiments of catalytic activities for toluene under the condition of relative humidity 70%show that the catalytic activity of these four catalysts all decreases,and with the partial substitutions of lanthanum by different atoms,their catalytic activity decreases differently,which means that they have different resistance to water vapor.The resistance to water vapor is La0.8Sr0.2CoO3>La0.8Ce0.2CoO3≈La0.8Ca0.2CoO3>La0.8Ba0.2CoO3,and their ΔT50% are about 12 ℃,20 ℃,20 ℃ and 50 ℃,which indicates that beside La0.8Ba0.2CoO3,the other three catalysts present some resistance to water vapor.Using XRD,BET and SEM,it is found that the decline of catalytic activity could be mainly ascribed that the competition of water molecules with toluene molecules for adsorption on the catalysts surfaces decreases the effective active sites for the catalytic combustion of toluene;and the formation of some new phases during high temperatures leads to the forming of rather dense coatings on the surface,blocking up the finely pores and the decreasing of specific surface area.