铈基与钴基Co3O4-CeO2氧载体上甲烷化学链转化特性: 产物选择性控制

采用水热法制备了Co₃O₄/CeO₂(x)[x为钴铈原子摩尔比n(Co):n(Ce)=6:49:1]和Ce_1-yCo_yO_2-δ(y=0.10.4)2个系列复合氧化物, 并表征了材料的物理化学性质, 考察了这些氧化物作为氧载体参与甲烷化学链转化(化学链燃烧和化学链部分氧化)的反应性能. 结果表明, 2类复合氧化物的甲烷反应活性均明显优于单一氧化物CeO₂或Co₃O₄, 但2类氧载体上的甲烷反应产物的选择性具有明显差异. Ce_1-yCo_yO_2-δ氧载体形成了Ce-Co-O固溶体, 储氧能力明显增强, 体相晶格氧迁移速率与甲烷活化速率匹配较好, 甲烷反应产物以CO和H₂的合成气为主, 有利于甲烷的化学链部分氧化. Co₃O₄/CeO₂(x)氧载体中CeO₂与Co₃O₄之间的相互作用改善了材料的储氧能力和氧化活性, 其与甲烷反应时主要生成CO₂, 有利于甲烷化学链燃烧. 连续性化学链循环实验表明, 2类氧载体均具有较好的再生性能和循环稳定性.

Chemical Looping Conversion of Methane over CeO2-based and Co3O4-based Co3O4-CeO2 Oxygen Carriers:Controlling of Product Selectivity†

Two series of Co3O4/CeO2(x)[x is the molar ratio of cobalt and cerium atoms, n(Co)/n(Ce)=5∶5―9∶1] and Ce1-yCoyO2-δ(y=0. 1—0. 4) composite oxides were prepared by the hydrothermal method. The physicochemical properties of these oxides were characterized by means of X-ray powder diffraction ( XRD) , BET( Brunauer-Emmett-Teller) surface area, temperature-programmed reduction( TPR) and Raman spectrum technologies. The prepared materials were used as an oxygen carrier for chemical looping conversion of methane in a fixed-bed reactor. The results showed that both the Co3O4/CeO2(x) and Ce1-yCoyO2-δoxygen carriers exhibited higher reactivity for methane conversion than single cerium oxide and cobalt oxide. However, the selectivity of CO2 and CO in the CH4 reaction over the two types of samples are significantly different. Ow-ing to a larger surface area and the formation of Ce-Co-O solid solution, the oxygen storage capacity of Ce1-y CoyO2-δoxygen carrier was improved significantly. Moreover, the reaction of Ce1-yCoyO2-δwith methane mainly generated CO and H2 due to good matching between the lattice oxygen mobility and the methane activation rate. On the other hand, the strong interaction between CeO2 and Co3 O4 also strongly enhanced the oxygen storage capacity and activity of Co3O4/CeO2(x) oxygen carriers. But they mainly concerted the methane to CO2 and H2 O owning to the relatively high concentration of active oxygen. In conclusion, the Co3 O4/CeO2 ( x ) composite oxides can be used as oxygen carriers for chemical looping combustion of methane, while the Ce1-yCoyO2-δ oxidesare more suitable for the chemical looping partial oxidation of methane to produce syngas. The sequential cyclic reaction experiments indicated that both the two types of oxygen carriers showed high stability during the successive redox testing.