含氧化镧的甲烷氧化偶联催化剂的一些特性

PROPERTIES OF LANTHANA-BASED CATALYSTS FOR THE OXIDATIVE COUPLING OF METHANE

利用ＤＴＡ、ＴＰＤ－ＭＳ、ＸＲＤ、ＴＰＲ及ＴＰＳＲ－ＭＳ等手段对Ｌａ＿２Ｏ＿３和含Ｌａ＿２Ｏ＿３的甲烷氧化偶联催化剂进行了研究。实验发现含Ｌａ＿２Ｏ＿３的催化剂的一个特点是其容易吸水，此时，催化剂中除含Ｌａ＿２Ｏ＿３外，还有Ｌａ（ＯＨ）＿３及Ｌａ＿２Ｏ＿３ＣＯ＿２存在。ＴＰＲ及ＴＰＳＲ结果表明了催化剂的起始氢气还原温度与纯甲烷的程序升温反应开始温度的一致性，这说明催化剂的晶格氧参与了甲烷的活化过程。不同的氧化物由于其晶格氧的活性不同，因而其活化甲烷的温度不同。Ｌａ＿２Ｏ＿３中的晶格氧非常活泼，它在７３０℃时即可以与甲烷或与Ｈ＿２反应而本身被还原。甲烷和氧气共进料时的程序升温反应（ＴＰＳＲ－ＭＳ）表明甲烷氧化偶联反应中Ｃ＿２烃的选择性有一最佳温度范围。

Lanthana and lanthana-containing catalysts for the oxidative coupling ofmethane(OCM ) were studied by temperature-programmed reaction(TPR), XRD, DTAand TPD-MS methods. It was observed that the lattice oxygen of lanthana can activatemethane at about 730℃. The reactivity order of the lattice oxygen in these catalysts is asfollows : La_2O_3>La-CaO>La-Sr-CaO≈Sr-CaO≈CaO. The starting temperature of theOCM reaction on lanthana-containing catalysts was lower than that on non lanthana-containing catalysts. Temperature-programmed reaction studies showed that there is anoptimal temperature range for the production of C_2 hydrocarbons, Another property oflanthana-containing catalyst is that it is easily hydrated by moisture in air. A La_2O_2CO_3phase probably exists under reaction conditions. However, the existence of La(OH )_3 andLaOOH is less likely because they decompose readily below 700℃.