Evolution of nickel speciation during preparation of Ni-SiO(2) catalysts: effect of the number of chelating ligands in [Ni(en)x(H2O)6-2x]2+ precursor complexes

Physical Chemistry Chemical Physics : PCCP
Ke-Qiang SunMichel Che

Abstract

The evolution of nickel speciation during the successive preparation steps of Ni-SiO(2) catalysts is studied by UV-Vis-NIR, FT-IR, DTG, TPR and TEM. The study focuses on the effect of the number of chelating ligands in the precursor complexes [Ni(en)(x)(H(2)O)((6-2x))](2+) (en = ethylenediamine, x = 1, 2, 3) on the adsorption on silica, and on nickel speciation after thermal treatment. When the en:Ni ratio in solution increases from 1 to 3, the most abundant complex is [Ni(en)(H(2)O)(4)](2+) (64% of all Ni complexes), [Ni(en)(2)(H(2)O)(2)](2+) (81%) and [Ni(en)(3)](2+) (61%), respectively. Equilibrium adsorption of [Ni(en)(x)(H(2)O)((6-2x))](2+) on SiO(2) results in the selective grafting of [Ni(en)(H(2)O)(4)](2+) and [Ni(en)(2)(H(2)O)(2)](2+), through the substitution of two labile H(2)O ligands by two surface SiO(-) groups. The surface [Ni(en)(H(2)O)(2)(SiO)(2)] complex formed by the grafting of [Ni(en)(H(2)O)(4)](2+) onto silica tends to transform into NiO and nickel phyllosilicate after calcination, which consequently leads to large and heterogeneously distributed metallic Ni particles upon reduction. In contrast, [Ni(en)(2)(SiO)(2)], resulting from the grafting of [Ni(en)(2)(H(2)O)(2)](2+) onto silica, no longer has aqua l...Continue Reading

References

Aug 10, 2004·Chemphyschem : a European Journal of Chemical Physics and Physical Chemistry·Souhir BoujdayMichel Che

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Citations

Nov 4, 2009·Journal of the American Chemical Society·Leticia Espinosa-AlonsoBert M Weckhuysen
May 22, 2008·Chemistry : a European Journal·Manuel BacaJuliette Blanchard
Oct 17, 2009·Chemistry : a European Journal·Theano PetsiKyriakos Bourikas
Jul 24, 2013·Chemical Communications : Chem Comm·Chengxi ZhangJinlong Gong
Jan 19, 2011·Chemistry : a European Journal·Kyriakos BourikasAlexis Lycourghiotis
Jun 20, 2015·Chemical Reviews·Peter MunnikKrijn P de Jong

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