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Characterization of Ni/SiO2Catalysts Prepared by Successive Deposition and Reduction of Ni2+Ions

Journal of Catalysis
Publication Date
DOI: 10.1006/jcat.1999.2521


Abstract Different Ni/SiO 2 specimens have been synthesized by impregnation (sample Ni– i–Si) and grafting Ni 2+ ions from nickel amminocomplex solution on (i) SiO 2 (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 Ni 2+ 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 Ni 2+ 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–1–Si sample (ca. 2 nm in diameter), the CO adsorption reveals the lack of dense crystal planes. The reduced Ni– i–Si sample is characterized by a lower dispersion of nickel (main diameter of the metal particles of 16 nm). Exposure of the reduced Ni–1–Si sample to oxygen causes oxidation of all of the surface situated metal nickel to Ni 2+. These Ni 2+ 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 Ni 2+ 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 Ni 2+ ions on silica can be used to prepare highly dispersed nickel catalysts with different nickel concentration.

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