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CO_2的化学转化具有环境及科学双重研究意义.CO_2具有很高的化学稳定性,加氢还原是一种有效的转化途径.其中将CO_2选择性还原为CO,即逆水汽变换(RWGS)反应(CO_2+H_2→CO+H_2O),具有重要的理论意义和应用价值:(1)CO作为合成气的重要原料,可以通过F-T合成生产更有价值的液体燃料;(2)H_2可通过可再生能源电解水制取,实现了全过程的零排放碳循环利用.从热力学角度分析,RWGS反应是一个吸热反应,高温有利于平衡转化率的提高.从动力学角度,一个对正反应有活性的催化剂可同时催化逆反应进行.可还原性载体负载贵金属催化剂,如Pt/Ce O_2,Au/Fe Ox,Au/Ce O_2等,具有很好的低温WGS催化活性,但它们在RWGS反应上的研究较少.我们制备了Ce O_2负载纳米Au催化剂(HRTEM表征结果表明金高度分散于Ce O_2载体表面,粒径为4–5 nm),其在常压CO_2加氢还原为CO反应中表现出优异的低温活性,分别在450°C,CO_2/H2=1,WHSV=12000 m L/(h·g),及400°C,H_2/CO_2=1,WHSV=6000 m L/(h·g)条件下,CO_2转化率接近平衡转化率,且CO的选择性为100%.随着H2/CO_2比例增加,CO_2转化率明显提高,且维持H_2/CO_2为1的化学计量比反应.通过原位漫反射红外光谱与质谱相结合的技术,研究了Au/Ce O_2催化剂上的RWGS反应路径:Au/Ce O_2催化剂表面形成了甲酸盐中间物种,它的消耗伴随着CO和H_2O产物的生成.说明Au/Ce O_2催化剂遵循中间体机理,这应该是其具有优异低温RWGS反应性能的微观机制.
The chemical conversion of CO 2 has the dual significance of environment and science.CO 2 has high chemical stability and hydrogenation reduction is an effective way to convert CO 2 to CO, that is, RWGS reaction CO 2 + H 2 → CO + H 2 O) has important theoretical significance and application value: (1) CO, as an important raw material for syngas, can be used to produce more valuable liquid fuels by FT synthesis; (2) H 2 can be produced through renewable energy sources The electrolysis of water to obtain, to achieve the entire process of zero-emission carbon recycling.From the thermodynamic point of view, RWGS reaction is an endothermic reaction, high temperature is conducive to the balance of conversion rate.From the kinetic point of view, a positive reaction is active Catalysts can catalyze the reverse reaction at the same time.Reducing catalysts supported noble metal catalysts, such as Pt / CeO_2, Au / FeOx, Au / CeO_2 and so on, have good low temperature WGS catalytic activity, but their RWGS reaction studies Less.We prepared Ce O 2 supported nano-Au catalyst (HRTEM characterization results show that the gold highly dispersed in the Ce O 2 carrier surface, the particle size of 4-5 nm), which in the atmospheric pressure CO 2 hydrogenation to CO reaction showed excellent Low temperature activity, respectively, at 450 Under the condition of 400 ℃, H 2 / CO 2 = 1, WHSV = 6000 m L / (h · g), C 2 CO 2 / H 2 = 1 and WHSV = 12000 m L / And the selectivity of CO was 100%. As the ratio of H2 / CO 2 increased, the conversion of CO 2 increased obviously, and the stoichiometric ratio of H 2 / CO 2 was maintained at 1. With the combination of in situ diffuse reflectance infrared spectroscopy and mass spectrometry , The RWGS reaction pathway on Au / Ce O 2 catalyst was studied: the formate intermediate species formed on the surface of Au / Ce O 2 catalyst, and its consumption was accompanied by the formation of CO and H 2 O. The results show that the Au / Ce O 2 catalyst follows the middle This should be the microscopic mechanism of its excellent low temperature RWGS reactivity.