Autothermal reforming of CH4 over supported Ni catalysts prepared from Mg–Al hydrotalcite-like anionic clay
Autothermal reforming of CH4 over supported Ni catalysts prepared from Mg–Al hydrotalcite-like anionic clay
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DOI：
10.1016/j.jcat.2003.07.001
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发表时间：
2004
影响因子：
7.3
通讯作者：
K. Takehira;T. Shishido;Peng Wang;Tokuhisa Kosaka;K. Takaki
中科院分区：
文献类型：
--
作者：
K. Takehira;T. Shishido;Peng Wang;Tokuhisa Kosaka;K. Takaki
以 Mg 位点含 Ni 的 Mg-Al 类水滑石化合物为前驱体制备了 spc-Ni/MgAl（spc：固相结晶法）催化剂，并测试了 CH4 部分氧化成合成气的性能。采用共沉淀法制备了基于[Mg2+1−xAl3+x(OH)2]x+(CO3−x) mH2O的前驱体，其中Mg/Al的比例变化，部分Mg2+离子被Ni2+离子取代，经热分解和还原形成spc-Ni/MgAl催化剂。 spc-Ni/MgAl 催化剂的表面积约为 150 m2gcat−1。 Ni2+离子首先取代了类Mg-Al水滑石化合物中的部分Mg2+位点，然后分解后并入混合氧化物中的岩盐型Mg-Ni-O固溶体中。因此，在 spc 制备过程中，Ni 的分散性不断增强，还原后得到高度分散的 Ni 金属颗粒。当 Mg/Al 比例为 1/3 时，spc-Ni/MgAl 催化剂的活性最高。当催化剂在 CH4 部分氧化中进行测试时，spc-Ni0.5/Mg2.5Al 即使在高空速 (9×105mlh−1gcat−1) 下也能提供足够高的 CH4 转化率，超过 1 wt% Rh/MgO 所获得的值。 spc-Ni0.5/Mg2.5Al催化剂上的Ni物种即使在O2存在下也很稳定，而传统浸渍制备的Ni催化剂由于Ni颗粒的表面氧化而很快失去活性。此外，在测试的催化剂中，反应产生的总热量比 spc-Ni0.5/Mg2.5Al 催化剂最低。这有力地表明，CH4 放热燃烧生成 H2O 和 CO2 的热量可能会被随后在 spc-Ni0.5/Mg2.5Al 上通过 H2O 和 CO2 进行的吸热 CH4 重整所消耗。因此，spc-Ni0.5/Mg2.5Al催化剂是CH4自热重整的一个有希望的候选者，它可以在H2O和O2共存下进行，以经济地将H2供给燃料电池。实际上，CH4的自热重整已经在spc-Ni0.5/Mg2.5Al催化剂上成功进行。
spc-Ni/MgAl (spc: solid-phase crystallization method) catalysts have been prepared from Mg–Al hydrotalcite-like compounds containing Ni at the Mg site as the precursors and tested for partial oxidation of CH4into synthesis gas. The precursors based on [Mg2+1−xAl3+x(OH)2]x+(CO3−x) mH2O, in which a ratio of Mg/Al varied and a part of the Mg2+ions were replaced by Ni2+ions, were prepared by a coprecipitation method, thermally decomposed, and reduced to form spc-Ni/MgAl catalyst. Surface areas of spc-Ni/MgAl catalysts were around 150 m2gcat−1. Ni2+ions first substituted a part of the Mg2+sites in the Mg–Al hydrotalcite-like compounds and then incorporated in the rock-salt-type Mg–Ni–O solid solutions in the mixed oxide after the decomposition. The dispersion of Ni was thus repeatedly enhanced during the spc preparation, resulting in the highly dispersed Ni metal particles after the reduction. The activity of the spc-Ni/MgAl catalyst was the highest at the ratio of Mg/Al of 1/3. When the catalysts were tested in the partial oxidation of CH4, spc-Ni0.5/Mg2.5Al afforded enough high CH4conversion even at the high space velocity (9×105mlh−1gcat−1), exceeding the value obtained over 1 wt% Rh/MgO. Ni species on spc-Ni0.5/Mg2.5Al catalysts were stable even under the presence of O2, while Ni catalysts prepared by the conventional impregnation quickly lost activity due to the surface oxidation of Ni particles. Moreover, the total heat produced by the reaction was the lowest over the spc-Ni0.5/Mg2.5Al catalyst among the catalysts tested. This strongly suggests that the heat of exothermic CH4combustion to H2O and CO2could be quickly consumed by the following endothermic CH4reforming by H2O and CO2over spc-Ni0.5/Mg2.5Al. Thus, the spc-Ni0.5/Mg2.5Al catalyst is a hopeful candidate for the autothermal reforming of CH4which can be carried out under the copresence of both H2O and O2to feed H2to the fuel cell economically. Actually the autothermal reforming of CH4has been successfully carried out over spc-Ni0.5/Mg2.5Al catalysts.