Metal particle size in Ni/SiO2 materials prepared by deposition-precipitation:: Influence of the nature of the Ni(II) phase and of its interaction with the support

The influence of the parameters of the deposition-precipitation method used to prepare Ni/SiO2 samples on the size of nickel metal particles was investigated by temperature-programmed reduction, transmission electron microscopy, and thermogravimetry. The results show that the average metal particle size, which varies between 27 and 79 Angstrom, depends on the nature and the reducibility of the supported Ni(II) phase (nickel hydroxide or 1:1 nickel phyllosilicate), and on the extent of the interface between the supported Ni(II) phase and silica. These parameters themselves depend on the characteristics of the silica support (surface area and morphology) and on the preparation parameters (urea and silica concentrations). At the interface, a nickel phyllosilicate is detected whatever the nature of the supported Ni(II) phase. The metal particles are smaller and the size distribution is narrower when the supported phase is a 1:1 nickel phyllosilicate ((d) over bar less than or equal to 50 Angstrom, 10-100 Angstrom) than when it is a nickel hydroxide ((d) over bar approximate to 80 Angstrom, 20-280 Angstrom). The metal particles are smaller when the extent of the Ni(II) phase-silica interface increases. This arises from the comparison of Ni/SiO2 samples prepared from silicas of high and low surface area, and from nonporous and porous silica.