| Much more attentions have been attracted to the global environmental problem i.e. the greenhouse effect, which resulted from the huge CO2 emissions. In addition, CO2 has been regarded as one of most abundant carbon source on the earth. As far as using the carbon source and solving the environmental problem concerned, the study on methanation of CO2 has been considered as a strategic task. Furthermore, the methanation of CO2 has been used in various industrial processes. For example, during ammonia synthesis and other hydro-procedures, the feed gases should be purified by the procedure of CO and CO2 methanation. For the ammonia synthesis catalyzed by Ru/C, the methanation of carbon support in the reaction environment has been regarded as the major defect. However, the fundamental studies on the methanation of carbon support with hydrogen have not been conducted. Moreover, Ru/C has been believed to be able to resist the poison of a trace CO2, CO and H2O in synthetic gas for ammonia synthesis, while it has been not revealed that whether the gasification of support carbon and CO2 would take place during the synthesis process. Therefore, in this dissertation it has been highlighted that the tests of the methanation behaviors of Ru catalysts supported on oxides or carbon in the mixture gas of CO2 and H2, and the gasification and methanation behaviors of carbon support of Ru/C under temperature of hydrogenation of CO2 in the three atmospheres i.e. the mixture gas of CO2andH2,CO2orH2.The methanation performances of a series of 7-Al2O3 supported transition metal catalysts have been explored by the employment of activity test. The order of catalytic activity (CO2 conversion) is shown as follows: Ru/ -Al2O3>Co/ -Al2O3> Ni/ -Al2O3 >Cu/ -Al2O3 >Pd/ -Al2O3. Among the catalysts, Ru/ -Al2O3 catalyst has the highest activity for the hydrogenation of CO2 with the least activation energy.The effect of supports on the hydrogenation of CO2 of Ru catalysts has been investigated. The order of activity is shown as follows: Ru/TiO2 > Ru/ZrO2 > Ru/MgO>Ru/Al2O3>Ru/ORu/SiO2, which can not be ascribed to the change of specific surface area of supports. This result is generally attributed to the electrondonation of transition metal oxides.The influences of Ru loading and preparation method of Ru/y-AhOj on the activity of catalysts have been investigated. The catalytic activity will be increased with the increase of the Ru loading. Compared with the catalyst prepared by impregnation method, the catalyst prepared by alcohol reduction method performs higher activity due to the finer Ru particle and narrow distribution of particle size.The behaviors of Ru/C in the three atmospheres i.e. the mixture gas of CO2 and H2, CO2 or H2 have been studied. The experimental results showed that there are three reactions: methanation of CO2 and H2, the methantion of carbon and hydrogen, and the gasification of carbon and CO2 in the reaction system, which occur simultaneously. The gasification of carbon with CO2 is more significant than the methanation of carbon with hydrogen at 400 . Furthermore, the present of H2 in the reaction system could restrain the gasification reaction of carbon support with CO2. The carbon loss rate will increase with the increase of reaction temperature.The influences of Ru loading, promoters and preparation condition on activity of Ru/C catalyst have been investigated, the conversion of CO2 and the selectivity to CH4 increase with the increase of Ru loading. As Ru loading of Ru/C is greater than 5 wt%, the selectivity to CH4 will be over 100 %. The addition of promoters of VIII metal and non-VIII metal into the single Ru metal catalyst will result in the decrease of catalytic activity. The carbon loss of catalyst can be resisted by the addition of K promoter. For the preparation of Ru/C catalyst for hydrogenation of CO2, the suitable impregnation time and reduction temperature should be 24 h and 200 掳C respectively.The optimal reaction conditions are space velocity 7200h-1, 1:4 of ratio of CO2 and H2, and... |
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