LiMn2O4/TiO2催化剂上甲烷氧化偶联反应性能的研究

Performance of oxidative coupling of methane on LiMn2O4/TiO2 catalysts

  • 摘要: 采用固相反应法制备了具有尖晶石结构的LiMn2O4/TiO2系列催化剂, 探讨了TiO2、Li/TiO2、Mn/TiO2、LiMn2O4及LiMn2O4/TiO2等不同组成催化剂的甲烷氧化偶联反应性能, 采用XRD、XPS、CO2-TPD和H2-TPR等表征方法对该系列催化剂进行了分析。结果表明, 具有尖晶石结构的LiMn2O4化合物具有较高的甲烷氧化偶联催化活性, 在775℃、0.1MPa、7200mL/(h·g), CH4:O2(体积比) 为2.5的条件下, 甲烷转化率可达25.8%, C2选择性可达43.2%。TiO2的存在不仅进一步提高了甲烷转化率和C2选择性, 还有效抑制了甲烷完全氧化形成CO2的过程。负载8% LiMn2O4的LiMn2O4/TiO2催化剂性能达到最优, 此时甲烷转化率达到31.6%, C2选择性为52.4%, CO2选择性降低到26.3%。考察了不同焙烧温度对催化剂活性的影响, 850℃为LiMn2O4/TiO2催化剂的最佳焙烧温度。

     

    Abstract: A series of LiMn2O4/TiO2 catalysts with spinel crystal structure were prepared by solid state reaction method, and the catalytic performance of oxidative coupling of methane on the different catalysts, such as TiO2, Li/TiO2, Mn/TiO2, LiMn2O4 as well as LiMn2O4/TiO2, was evaluated. The catalysts were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, CO2 temperature programmed desorption and H2 temperature programmed reduction. It is found that LiMn2O4 with spinel structure has high catalytic activity in oxidative coupling of methane reaction. 25.8% of CH4 conversion, 43.2% of C2 selectivity was obtained under the reaction conditions of 775℃, 0.1MPa, 7200mL·h-1·g-1, CH4:O2(volume ratio)=2.5. The introduction of TiO2 support can not only improve CH4 conversion and C2 selectivity, but also restrain the deep oxidation of methane to CO2. The LiMn2O4/TiO2 with 8% loading amount showed the best activity, on which 31.6% of CH4 conversion, 52.4% of C2 selectivity were obtained and CO2 selectivity was decreased to 26.3%. The effect of calcination temperature on the activity of LiMn2O4/TiO2 catalysts was investigated. 850℃ is the optimal calcination temperature.

     

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