甲烷在二元碱土金属复合体系催化剂上的氧化偶联

Oxidative Coupling of Methane over Alkaline Earth Compound Catalysts

碱土金属氧化物或碳酸盐为多种类型甲烷氧化偶联制取C_2烃催化剂的重要组分之一.有关纯碱土金属氧化物及含氧酸盐的研究表明,这类化合物具有较强的表面碱性及高温P型半导性而对活化甲烷生成C_2烃有较高活性,关于不同碱土金属化合物之间混合形成的二元碱土金属复合体系催化剂的报导仍不多见,Aika等人曾报导用BaO与CaO或MgO混合的催化剂上在1073K时可以获得61.1%C_2烃选择性和14.2%的C_2烃收率,但BaO易在反应条件下与水反应生成Ba(OH)_2而腐蚀器壁,不利于长期操作.本文报导了一系列不同碱土金属化合物之间形成的二元碱土复合体系催化剂上甲烷氧化偶联的反应结果.结果表明,这类催化剂由于其结构稳定、活性好而值得进一步研究.

The properties and structures of alkaline earth compound systems as essential catalysts for the oxidative coupling of methane were studied. Among these ctalysts, MgO/BaCO3 was found to be the best one. Experimental results show that the activity of MgO/ BaCO3 is affected by different preparation methods. The catalyst prepared by impregnation has lower activity and the catalyst prepared by slurring method shows higher activity than the catalysts made by other methods. The structural characterization indicates that the higher porosity and properly lower specific surface area are beneficial. As the content of MgO increases, the methane conversion has a maximum and the C2 selectivity decreases slowly. It is indicated that the MgO is the active component, and the addition of BaCO3 can improve the surface structure and prohibit deep oxidation. 530-hour stability run shows that ine MgO/ BaCO3 catalyst was stable during this period. FTIR spectra and XRD analyses show no crystal change of MgO/BaCO3 catalyst after this run. The results of stability experiment at 780℃, GHXV = 2. 56 × 104 are: C2 selectivity 68% , C2 yield 16. 3%.