LiCl/SO_4^(2-)ZrO_2催化剂上乙烷氧化脱氢制乙烯

Oxidative Dehydrogenation of Ethane to Ethylene over LiCl/SO_4^(2-)-ZrO_2 Catalyst

用辅以回流处理的两步法制备硫酸化氧化锆(SO2-4ZrO2),再用浸渍法制备Li质量含量为0.5%～15%的LiCl/SO2-4ZrO2催化剂.650℃时,在Li含量为15%的催化剂上,获得了90.6%的乙烷转化率、85.9%的乙烯选择性和77.8%的乙烯收率,在24h的实验考察中,乙烯的收率一直保持在71%以上.采用X射线粉末衍射、低温N2吸附、程序升温脱附和X射线光电子能谱等对催化剂的体相结构、比表面积、表面酸碱性和表面元素组成等进行了表征.结果表明,LiCl的添加使催化剂中四方相ZrO2的含量降低,比表面积减小,表面酸性减弱,乙烷氧化脱氢催化性能明显提高,但ZrO2的体相结构对其催化性能没有明显影响.随着反应时间的延长,LiCl慢慢流失,催化剂的乙烯选择性逐渐下降.与未经回流处理制得的硫酸化二氧化锆相比,采用回流处理后的ZrO2制得的SO2-4ZrO2具有较大的比表面积,单位质量的样品可负载更多的LiCl,有利于延缓催化剂活性因LiCl流失而下降.

Sulfated zirconia （SO4^2--ZrO2） samples were prepared by a modified two-step method （refluxing ZrO（OH）2 precursor in basic solution followed by drying and （NH4）2SO4 impregnation） and then impregnated with a LiCl solution to give the SO4^2--ZrO2-supported LiCl catalysts with Li mass content of 0.5 % - 15 %. The catalysts were characterized by X-ray diffraction, scanning electron microscopy, N2 adsorption, temperature-programmed desorption-mass spectrometry, and X-ray photoelectron spectroscopy. The results show that with increasing LiCl loading, the specific surface area and acidity of the catalysts as well as the volume fraction of tetragonal zirconia in the catalysts decrease, while the catalytic performance of the catalysts for oxidative dehydrogenation of ethane （ODHE） to ethylene increases. Over the LiCl/SO4^2--ZrO2 catalyst with a Li content of 15 %, the ethylene yield of 77.8 % with an ethane conversion of 90.6% is achieved at 650℃, and the yield higher than 71% is maintained over a period of 24 h. The textural structure of ZrO2 has little effect on the catalytic behavior of the LiCl/SO4^2--ZrO2 catalysts. The specific surface area of SO4^2--ZrO2 samples prepared by the modified two-step method is much bigger than that of the SO4^2--ZrO2 samples made by the method reported in literature, and therefore more LiCl can be loaded on unit mass of support. This is favorable to improve the catalyst stability and slow down catalyst deactivation during the ODHE reaction due to the loss of LiCl.