La_2O_3-BaO系复氧化物的现场拉曼光谱研究

In-situ Raman Spectroscopic Study of La 2O 3-BaO Catalysts

对于Ｌａ０．２Ｂａ０．８－ｘＣａｘ（Ｏ，ＣＯ３）其中ｘ＝０．０、０．２、０．４、０．６氧化物在９７３Ｋ及甲烷氧化偶联（ＯＣＭ）条件下，无Ｃａ２＋的样品可用表面ＢａＣＯ３和（ＬａＯ）２ＣＯ３的Ｒａｍａｎ谱及８１０ｃｍ－１附近的Ｏ２－２特征峰来表征；含Ｃａ２＋的样品，则表现了混合碳酸盐（Ｃａ，Ｂａ）ＣＯ３的特征，还有位于１１３５ｃｍ－１（ｗ）和８１０ｃｍ－１（ｗ）的Ｏ－２、Ｏ２－２瞬时态氧物种；９７３～１０５３Ｋ发现ＯＣＭ反应活性随温度和Ｃａ２＋含量而增加，Ｃ２烃选择性也随ＯＣＭ反应温度增大；１０５３Ｋ时，Ｃａ２＋含量的增加，Ｃ２烃选择性略有下降，这些结果指出Ｏ－２是ＯＣＭ反应的活性氧物种，它在较高温度下与ＣＨ４作用，且具有较好的Ｃ２烃选择性和较大的反应活化能。

For a series of La-Ba-Ca-(O,CO 3) catalysts under methane-oxidative-coupling conditions at 973K,the Ca-free sample was characterized by Raman bands due to surface carbonates of BaCO 3 and (LaO) 2(O,CO 3) phases,and a weak and broad band around 810cm -1 ,probably due to O 2- 2;the Ca-containing samples showed Raman bands of surface carbonates associated with (Ba,Ca)CO 3 phase and minor amount of BaCO 3 phase (but not with lanthania phase),and active-oxygen bands at 1135cm -1 (w) and 810cm -1 (w,br) attributed to O - 2 and O 2- 2 transient species,respectively.At 973～1053K,the activities of all the samples were found to increase with increasing OCM temperature and with increasing calcium contents.The C 2-selectivities increased with increasing temperature for all the samples,and increased with increasing calcium contents at 973K,but decreased slightly with increasing calcium contents at 1053K.These results strongly indicate that O - 2 might be an active oxgen-species reacting with CH 4 with higher C 2-selectivity and higher activation energy,becoming sufficiently active only at higher temperature.