CeO_(2)-Al_(2)O_(3)复合载体负载Ni基催化剂催化COx共甲烷化性能

COx co-methanation over a Ni-based catalyst supported on CeO_(2)-Al_(2)O_(3) composite

通过浸渍沉淀法分别制备Ni/Al_(2)O_(3)、Ni/CeO_(2)和Ni/CeO_(2)-Al_(2)O_(3)催化剂,并对其分别进行不同CO/CO_(2)比例下COx共甲烷化性能评价。发现Ni/Al_(2)O_(3)催化剂催化CO转化为CH4的能力明显高于Ni/CeO_(2),而催化CO_(2)甲烷化的性能则相反。采用Ni/CeO_(2)-Al_(2)O_(3)催化剂,可以在提高CO转化率的同时而不降低CO_(2)转化率。结合BET、XRD、TPR、TPD和原位红外等各种表征手段,发现CeO_(2)掺杂虽然降低了催化剂的比表面积和金属Ni的分散度,但却可明显提高其吸附活化CO_(2)的能力,这主要是由于具有较高含量氧空位的CeO_(2)的掺杂可以提高载体表面碱性位,促使共甲烷过程中CO_(2)吸附活化并形成单齿碳酸盐,通过快速加氢反应生成目标产物甲烷;而Ni/Al_(2)O_(3)受限于其对CO_(2)的吸附容量和活化产物双齿碳酸盐的活性,在催化共甲烷化体系中只能获得较低的CO_(2)转化率,但CO转化率不受影响。

Ni/Al_(2)O_(3),Ni/CeO_(2) and Ni/CeO_(2)-Al_(2)O_(3) catalysts were prepared by impregnation-precipitation method and applied for COx co-methanation with different ratios of CO/CO_(2).It was found that the conversion of CO to CH4 was higher over Ni/Al_(2)O_(3) than that over Ni/CeO_(2),while CO_(2) methanation gave reverse order.Adopting Ni/CeO_(2)-Al_(2)O_(3) as COx co-methanation catalyst improved the CO conversion without lessening CO_(2) conversion.BET,XRD,TPR,TPD and in-situ FTIR characterizations showed that the surface area and dispersion degree of metallic nickel decreased after CeO_(2) was dopped in Al_(2)O_(3).However,the CO_(2) adsorption and activation capacity were increased,because the rich oxygen vacancies on CeO_(2) would increase the basic sites on the support which activated CO_(2) to monodentate carbonate,and then be hydrogenated to methane quickly.Limited by the CO_(2) adsorption capacity and the activity of the medium product-bidentate carbonate,the CO_(2) conversion over Ni/Al_(2)O_(3) catalyst was lower than that over Ni/CeO_(2)-Al_(2)O_(3) catalyst while CO conversion was unaffected during COx co-methanation.