CH_4-CO_2两步反应直接合成含氧有机物的研究——添加氢的影响

Study on Conversion of CH_4-CO_2 to Oxygenic Compounds at Low TemperatureThe Influence of Hydrogen

以热力学分析和动力学分析为基础 ,设计了几种实现CH4 CO2 低温转化直接合成含氧有机物的混氢进料方式 ,通过实验对这些进料方式进行了初步探讨 ,并考察了甲烷活化及二氧化碳反应过程中混氢比例的影响 .结果表明 ,与CH4 CO2 进料方式相比 ,几种混氢进料方式都能提高乙酸收率 ,但需要很好地控制二氧化碳加氢反应 .在甲烷活化过程中混氢 ,13 8%的氢气比例对甲烷的转化最有利 ,乙酸收率可达最高 ;在二氧化碳反应过程中混氢 ,混氢比例为 5 0 %时乙酸收率最高 .

Based on the thermodynamic and kinetic analyses in previous papers, three feed-ways of mixed hydrogen, CH_4/(CO_2-H_2), (CH_4-H_2)/CO_2 and (CH_4-CO_2)/H_2, have been contrived to convert directly CH_4 and CO_2 into oxygenic compounds in a two-step sequence. These feed-ways have been principally probed on Cu-Co, Ru-Co and Pd catalysts, and the influence of hydrogen content in both H_2-CO_2 and H_2-CH_4 has been also studied. Compared with CH_4/CO_2, all these feed-ways containing hydrogen can improve the yield of acetic acid. However, some measures should be adopted to control the competition of CO_2 hydrogenation. In (CH_4-H_2)/CO_2 feed-way, when the hydrogen content in H_2-CH_4 flow reaches 13.8%, the yield of acetic acid reaches the highest; in CH_4/(CO_2-H_2) feed-way, when the hydrogen content in CO_2-H_2 flow reaches 50%, the yield of acetic acid is the highest. The fresh and the used Cu-Co and Ru-Co catalysts have been characterized, and the surface element composition of the catalysts has been analyzed. For Cu-Co catalyst, after the reaction the Co is enriched on the catalyst surface in CH_4/CO_2 feed-way, but the Cu is enriched on that in the feed-ways of mixed hydrogen, which is consistent with their catalytic performance. For RuCo/13X zeolite catalyst, there is nooverlap between Ru and Co. The Co attaches equably to the support surface, but the Ru acts more with the component of support. In the reaction atmosphere, that Ru and Co are enriched on the catalyst surface is also consistent with their catalytic performance.