Characterization of Ni/SiO2 catalysts prepared by successive deposition and reduction of Ni2 ions
Characterization of Ni/SiO2 catalysts prepared by successive deposition and reduction of Ni2 ions
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DOI：
10.1006/jcat.1999.2521
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发表时间：
1999-07-25
影响因子：
7.3
通讯作者：
Mintchev, L
中科院分区：
文献类型：
--
作者：
Hadjiivanov, K;Mihaylov, M;Mintchev, L
通过浸渍法（样品Ni - i - Si）以及将来自镍氨配合物溶液的Ni²⁺离子接枝到（i）SiO₂（样品Ni - 1 - Si）和（ii）还原后的Ni - 1 - Si（样品Ni - 2 - Si）上，合成了不同的Ni/SiO₂样品。通过程序升温还原（TPR）、红外光谱、漫反射紫外 - 可见光谱、X射线光电子能谱（XPS）、X射线衍射（XRD）、透射电子显微镜（TEM）和铁磁共振（FMR）对它们进行了表征。由于表面硅酸盐的形成，来自Ni - 1 - Si的Ni²⁺离子酸性较低，并且仅在低温下形成羰基。与来自Ni - i - Si样品的Ni²⁺离子（在652和710 K有两个TPR峰）相比，它们具有更高的还原温度（在956 K有TPR峰）。Ni - 1 - Si样品还原后形成高度分散的金属颗粒（直径约2 nm），一氧化碳吸附表明缺乏致密的晶面。还原后的Ni - 1 - Si样品的特征是镍的分散度较低（金属颗粒的主要直径为16 mm）。还原后的Ni - 1 - Si样品暴露于氧气中会导致所有位于表面的金属镍氧化为Ni²⁺。这些Ni²⁺离子比最初沉积的更容易被还原（在489 K有TPR峰）。在镍还原过程中，部分二氧化硅表面得到再生，并且在氧化后不会再次被堵塞，这使得Ni²⁺离子能够随后沉积在还原后的催化剂上。结果，镍浓度增加。还原后的Ni - 2 - Si样品也具有小的镍颗粒（直径约2 - 3 nm）的特征。结果证明，在二氧化硅上随后进行Ni²⁺离子的沉积 - 还原可用于制备具有不同镍浓度的高度分散的镍催化剂。（C）1999学术出版社
Different Ni/SiO2 specimens have been synthesized by impregnation (sample Ni-i-Si) and grafting Ni2+ ions from nickel amminocomplex solution on (i) SiO2 (sample Ni-1-Si) and (ii) reduced Ni-1-Si (sample Ni-2-Si). They have been characterized by TPR, IR spectroscopy, DR UV-VIS spectroscopy, XPS, XRD, TEM, and FMR. Due to the formation of surface silicates, the Ni2+ ions from Ni-1-Si exhibits low acidity and forms carbonyls only at low temperatures. They are characterized by a higher reduction temperature (TPR peak at 956 K) than the Ni2+ ions from the Ni-i-Si sample (two TPR peaks at 652 and 710 K). Highly dispersed metal particles are formed after reduction of the Ni-l-Si sample (ca. 2 nm in diameter), the CO adsorption reveals the lack of dense crystal planes. The reduced Ni-1-Si sample is characterized by a lower dispersion of nickel (main diameter of the metal particles of 16 mm). Exposure of the reduced Ni-1-Si sample to oxygen causes oxidation of all of the surface situated metal nickel to Ni2+. These Ni2+ ions are reduced much more easily (TPR peak at 489 K) than those initially deposited. Part of the silica surface is regenerated during the reduction of nickel and is not blocked again after oxidation, which allows subsequent deposition of Ni2+ ions on the reduced catalysts. As a result, the nickel concentration increases. Reduced Ni-2-Si sample is also characterized by small nickel particles (ca. 2-3 nm in diameter). The results evidence that subsequent deposition-reduction of Ni2+ ions on silica can be used to prepare highly dispersed nickel catalysts With different nickel concentration. (C) 1999 Academic Press.