Na_2SnO_3系催化剂在甲烷氧化偶联反应中的催化性能及表面碱性的探讨

The Catalytic Properties and Surface Basicity of a Series of Na_2SnO_3 Catalysts for Oxidation Coupling of Methane

1982年Keller和Bhasin以金属氧化物为催化剂从甲烷制得少量乙烯和乙烷的工作引起了各国研究工作者的重视,此后报道了许多有研究价值的催化剂,其中添加碱金属对提高催化性能所起的作用引起了普遍的关注.Lunsford等首先用添加Li^+的MgO作催化剂,发现催化剂表面碱性增强的同时,生成C_2烃类产物的选择性明显增加.随后Iwamatu等在MgO中添加Na^+及Rb^+盐,Jones等在Mn^(4+)/SiO_2中添加Na^+,Otsuka等在Sm_2O_3中添加LiCl作为甲烷氧化偶联催化剂进行了研究,这些结果均表明。

In order to investigate the effect of surface basicity over catalysts of the oxidative coupling reaction of methane, SnO2 and Na2SnO3 catalysts with Li2SO2 as the additive were studied. The results showed that the addition of Li2SO4 resulted in increase of the surface basic sites and improving the catalytic performance. It was found that the series of Na2SnO3 catalysts were obviously better than the SnO2 series. The yield of C2 hydrocarbon over 5 mol % Li2SO4-Na2SnO3 catalyst reached 21. 5% when the reaction was carried out at the temperature of 800℃, with space velocity of 10000 ml ?g 1 ?h 1and CH4/O2 = 2. The addition of Fe3+ to 5 mol% Li2SO4- Na2SnO3 sample resulted in some decrease of CH4 conversion , while the C2selectivity increases, especially the C2H4 selectivity. The sample which had adsorbed CO2 were studied by temperature programmed desorption- mass spectrographic detection method (CO2- TPD-MS). The results indicated that besides the increase of surface basic sites, the relative content of weak basic centers also increases as the result of the addition of Li2SO4(and Fe3+), and that the relative content of weak basic centers was related to the C2 selectivity of catalysts.