Ba-La_2O_3催化剂的表面碱性、活性氧种对甲烷氧化偶联的影响

STUDY OF SURFACE BASICITY AND ACTIVE OXYGEN SPECIES OVER BaLa 2O 3 CATALYSTS FOR OXIDATIVE COUPLING OF METHANE

利用ＣＯ２ＴＰＤ技术考察了ＢａＬａ２Ｏ３系催化剂的表面碱性，实验发现，催化剂表面仅有单一的强碱位或中碱位时，其催化性能均较差。只有表面的中碱位与强碱位以适当量共同存在的样品（６％ＢａＬａ２Ｏ３），才能获得好的催化活性和Ｃ２选择性。此碱性特征可能有利于表面活性位的产生。同时利用ＸＲＤ和ＸＰＳ等技术分别对体相结构和表面氧物种进行了研究。结果表明，ＢａＬａ２Ｏ３系催化剂表面存在Ｏ２２离子，但Ｏ２２离子不可能是活化甲烷的独立氧物种，而是与α晶格氧共同存在时，有利于形成促使甲烷氧化偶联的表面复合活性位。６％ＢａＬａ２Ｏ３样品的高甲烷转化率和Ｃ２选择性正是归因于其表面上可能存在较多的这种复合活性位。

The oxidative coupling of methane (OCM) over BaLa 2O 3 catalysts is investigated The results show that it is advantageous to improve the catalytic ability by doping little content of barium species into La 2O 3, and 6%BaLa 2O 3 exhibits the best catalytic ability for OCM The surface basicity of BaLa 2O 3 catalysts has been studied by means of CO 2TPD The experiment indicates that the catalyst with only strong basicsite or medium strong basicsite on its surface has low activity while one with both of basic sites exhibits high catalytic activity and C 2 selectivity These mean that the active oxygen species (or active site) can be easily formed on this special basic surface The XPS study showes that O 2 2 species exist on the surface of BaLa 2O 3 catalysts and its content increases with increasing of barium component The 6%BaLa 2O 3 catalyst with more O 2 2 species and more lattice oxygen species showes high catalytic ability On the other hand, 44%BaLa 2O 3 exhibites low activity in spite of its larger content of O 2 2 species than others This study can be concluded that O 2 2 species itself cannot be the active oxygen species although it is important for OCM reaction unless it may be combines with other species to form the real active sites for OCM on the surface