Sol-gel processing of alkoxysilyl-substituted nickel complexes for the preparation of highly dispersed nickel in silica

摘要

Nanocomposites containing nickel nanoparticles in silica were obtained by sol-gel processing of Ni(NO_3)_2, Ni(OAc)_2 (OAc = acetate), NiCl_2, or Ni(acac)_2 (acac = aetylacetonate, a complexing silane [(EtO)_3Si(CH_2)_3NHCH_2CH_2NH_2, (EtO)_3Si(CH_2)_3NH_2 or (RO)_3Si(CH_2)_3NHCH_2CH_2NHCH_2NH_2] and Si(OEt)_4, followed by calcination of the metal-complex-containing xerogels in air and reduction in hydrogen. Two types of nanocomposite materials were prepared, both containing about 8-8.5wt% of element nickel: (i) Ni/SiO_2 nanocomposite powders in which the silica matrix is mainly formed from Si(OR)_4, and (ii) Ni particles on pre-formed silica spheres. The latter were prepared by impregnating silica spheres with sols from the particular complexing silane-nickel salt combination followed by calcination and reduction. In both types of materials, the average nickel particle size is influened by the composition of the precursor mixture, particularly the counter-ion of the employed nickel salt. The smallest particles (diameter belo 3 nm) were obtained from Ni(NO_3)_2 [and Ni(OAc)_2 for the powders], while the use of Ni(acac)_2 and NiCl_2 resulted in larger nickel particles. The variation of the nickel particle diameters was much larger for the powders than for the impregnated spheres.