Novel and effective surface enrichment of active species in Ni-loaded catalyst prepared from Mg–Al hydrotalcite-type anionic clay
Novel and effective surface enrichment of active species in Ni-loaded catalyst prepared from Mg–Al hydrotalcite-type anionic clay
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DOI：
10.1016/j.apcata.2004.10.010
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发表时间：
2005-01
影响因子：
5.5
通讯作者：
K. Takehira;T. Shishido;D. Shouro;K. Murakami;M. Honda;Tomonori Kawabata;K. Takaki
中科院分区：
文献类型：
--
作者：
K. Takehira;T. Shishido;D. Shouro;K. Murakami;M. Honda;Tomonori Kawabata;K. Takaki
利用镁铝水滑石的“记忆效应”制备了蛋壳型负载镍催化剂，并成功地用于甲烷水蒸气重整反应。首先通过热分解镁铝水滑石制备了Mg-Al（3/1）复合氧化物颗粒作为催化剂载体。当颗粒浸渍在硝酸镍（II）的水溶液中时，镁铝水滑石在颗粒的表面层中重构，同时Ni（II）取代Mg（II）位点，导致形成蛋壳型Ni负载。研究了制备Mg-Al（3/1）复合氧化物和浸渍硝酸镍溶液的条件对蛋壳型镍负载量和催化活性的影响。加热速率、Mg-Al（3/1）混合氧化物的最终煅烧温度、硝酸镍水溶液的pH值和混合氧化物在水溶液中的浸渍时间对蛋壳型Ni负载的形状有显著影响。较小的升温速率、较低的煅烧温度和较低pH值的水溶液浸渍有利于蛋壳型镍负载。在温和的加热条件下，形成了方镁石状MgO结构，在较低的pH值下浸渍时，通过“记忆效应”优先引发Mg-Al水滑石在颗粒表面的重组。由此得出结论：分散良好的Ni金属颗粒表面富集提高了蛋壳型Ni负载催化剂的活性。
Egg shell-type Ni loaded catalysts have been prepared by adopting the “memory effect” of Mg–Al hydrotalcite and have been successfully used in the steam reforming of CH4. Mg–Al(3/1) mixed oxide particles were first prepared as the catalyst support by the thermal decomposition of Mg–Al hydrotalcite. When the particles were dipped in aqueous solution of Ni(II) nitrate, Mg–Al hydrotalcite was reconstituted in the surface layer of the particles, and simultaneously Ni(II) substituted for the Mg(II) sites, leading to the formation of egg shell-type Ni-loading. The conditions of both preparation of Mg–Al(3/1) mixed oxide and dipping in Ni(II) nitrate solution were varied, and their influences on egg shell-type Ni-loading and on the catalytic activity were studied. The shape of egg shell-type Ni-loading was significantly affected by the rate of heating, the final calcination temperature of Mg–Al(3/1) mixed oxide, the pH of Ni(II) nitrate aqueous solution, and the dipping time of the mixed oxide in the aqueous solution. The smaller heating rate, the lower temperature calcination, and a dipping in the aqueous solution at the lower pH were preferable for the Ni-loading in egg shell-type. Under the mild heating conditions, periclase-like MgO structure was formed, on which the reconstitution of Mg–Al hydrotalcite was preferentially provoked in the surface layer of the particle by “memory effect” during the dipping at the lower pH. It is concluded that the activity of egg shell-type Ni-loaded catalyst was enhanced by the surface enrichment of well-dispersed Ni metal particles.