LiMO_2系列氧化物的甲烷氧化偶联活性

Oxidative Coupling of Methane over a Series of LiMO_2 Catalysts

固体氧化物浸入不同含量LiNO_3溶液,晾干后于750—800℃焙烧制成系列LiMO_2(M=Cr,Fe,Co,Hi,Al)型样品,在CH_4氧化偶联反应中作催化活性测定。结果表明,随着反应温度提高,C_2收率普遍增加。以5/5摩尔比Li_2-Fe_2O_3(Fe-50)及2/8摩尔比Li_2O-NiO_x(Ni-20)尤好。该样品在750—800℃下C_2收率均在10％以上,Fe-50于850℃下的C_2收率可达22％(产物中一半以上是乙烯)。10小时内催化活性无明显下降,其O_2转化率几乎始终未变。另外,Li、Fe氧化物中α-LiFeO_2晶相数量直接与活性成平行关系。

A series of lithium-doped oxides of transition elements catalysts was studied to determine the effect of lithium as a promoter for the oxidative coupling of methane. Of the catalysts tested, a 50 mol％ Li_2O-Fe_2O_3 (Fe-50) was the most active catalyst for the reaction. XRD analysis showed that the catalyst was the α-form of LiFeO_2, with a disordered cubic 'NaCl-type' structure. The deactivation of catalysts with reaction time was examined for Fe-50. The catalytic activities and product distribution did not change sharply after 10 hours. The oxygen conversion rate almost remained unchanged. The stability of the solid solution of Li with transition metal oxides under steady state reaction conditions is essential for the Li-doped oxides to be effective in the oxidative coupling of methane.