Abstract:

NiO-CeO₂/γ-Al₂O₃ oxygen carrier was prepared with the impregnation method and the effects of Ni/Ce mass ratios on the performance of chemical looping reforming hydrogen production were studied. The experiments with fixed bed reactor revealed that the selectivity of hydrogen first increased and then decreased as the ratio decreases. For the ratio of 3∶1, there was a maximal selectivity of hydrogen together with the highest concentration of hydrogen produced. The cycle test showed that the 3∶1 oxygen carrier still maintained good reaction activity and the lowest carbon deposited after 20 cycles. Meanwhile, the XRD results showed that addition of CeO₂ was leads to formation of Ce-O-Ni solid solution, which weakened the interaction between NiO and γ-Al₂O₃ to a certain extent, and subsequently increased oxygen vacancies and improved the dispersion of active materials. Further analyses on the XRD results indicated that the 3∶1 oxygen carrier had the smallest particle size, which was more conducive to hydrogen production by reaction. In fact, the microscopic morphology of the 3∶1 oxygen carrier particles only changes slightly after 20 cycles of testing according to SEM analyses. The further fixed bed experiments indicated that higher temperature was conducived to the hydrogen production reactions and the 3∶1 oxygen carrier performed significantly better than the others. Meanwhile, it was found the 3∶1 oxygen carrier could still maintain high product selectivity under higher water-to-carbon ratio.

Key words: chemical looping reforming, composite oxygen carrier, hydrogen production, fixed-bed, reactivity, methane

摘要：

采用浸渍法制备了结构型NiO-CeO₂/γ-Al₂O₃复合载氧体，研究了Ni/Ce质量比对化学链重整制氢反应性能的影响。固定床反应器实验表明，随着Ni/Ce质量比的降低，氢气的选择性先升高后降低，比例为3∶1时氢的选择性和氢产物浓度最高。循环实验测试表明，3∶1载氧体在20个循环后仍保持催化活性，积炭量最低。XRD结果表明，加入CeO₂后有固溶体形成，增加了氧空位，在一定程度上减弱了NiO与γ-Al₂O₃之间的相互作用，提高了活性物质的分散度。进一步分析XRD结果发现3∶1载氧体粒径最小，更有利于制氢反应。SEM分析发现，经过20次循环3∶1载氧体颗粒的微观形貌变化相对较小。进一步的固定床实验研究表明较高的反应温度有利于制氢反应，800℃时3∶1载氧体的性能表现最佳；此外3∶1载氧体在较高水碳比下仍能保持较高的产物选择性。

关键词: 化学链重整, 复合载氧体, 制氢, 固定床, 活性, 甲烷