i want to use TEOS as silica precursor in my catalyst preparation. My catalyst is cobalt based on silica.
precipitate the silica in what morphology? Adding a polycationic polymer will precipitate it and the MW of the polymer will determine the size of the silica particles. A lot of this work was pioneered by Kroger and Sumper (three articles published in Science) who figured this out based on the biomineralization capabilities of marine diatoms.
Hi Sonal,
I think what you are looking to do is a silica sol-gel polymerization synthesis method to make a porous silica structure or particles of which you could decorate the outside with your cobalt catalyst. For porous silica matrix where you will support the cobalt internally on I would suggest reading the following reference (this is just an example of an evaporation induced self-assembly micelle templated silica sol-gel synthesis of mesoporous silica and there are so many other types of silica structures that can be synthesized and methods for synthesizing as well, and its kind of relevant to what you are doing):
M. Josefina Perez Zurita, et al., HMS mesoporous silica as cobalt support for the Fischer–Tropsch Synthesis: Pretreatment, cobalt loading and particle size effects, Journal of Molecular Catalysis A: Chemical 2008, 281, 146-153
To generate particles this is easily accomplished by the Stoeber method. These will be mainly and approximately spherical or ellipsoidal, virtually non-porous (so like cabosil), and amorphous silica. See original publication by him:
W. Stoeber et al., Controlled Growth of Monodisperse Silica Spheres in the Micron Size Range, J. of Colloid & Interface Science 1968, 26, 62-69
But there have been numerous refinements of this first work by many other researchers over the years since then to synthesize silica particles by this solution based silica sol-gel polymerization synthesis method, so you can find more recent refs probably to better suit your specific application and needs. Hope this helps!
Regards,
Jacob H. Prosser
Currently there are many methods available to prepare silica particles with specific size ranges. The best one for non-porous, as Jacob wrote, is the traditional Stoeber method. This method can be adapted to the synthesis of porous silica just by adding a tempting agent (typically a surfactant). This modification is typically good for sub micron particles. Still, there are many good methods to go over microns, and because of that, you may want to be a little more specific in terms of the size range. This paper by Paul Wright (J. Mater. Chem., 2002, 12, 20–23), for example gives you conditions for SBA-2 that are about 1-2 microns across, or for SBA-2 plates 50 microns wide, or for hollow spheres that are about 100 microns.
You may also want to decide what pore size and type of pore morphology you are interested in. If you want micropores, mesopores or macro pores will depend on the catalytic process you are interested in (whether it involves small or large reactants, whether it is in flow or batch mode, whether it is in liquid or gas phase). You also would have to think whether you care about pore ordering or not, if want well-ordered pores you can also choose between 2D or 3D symmetries, and this may affect the accessibility of your active sites, the particle size of your catalyst (if it is Co or CoOx nanoparticles) and the chances of leaching the catalyst during the reaction.
There are many options. I hope this isn't confusing, and helps as a starting point. Best luck!
Strongly agreed with Jacob. Size of the silica is actually can be controlled with few parameters if via sol-gel process.
I think according to our experience the best way is as follows:
dissolve TEOS and cobalt nitrate and oxalic acid in ethanol separately at about 70C. Then add the TEOS and cobalt nitrate solution under mixing at constant temperature. at the second stage oxalic acid solution was added under prefect mixing. In this way you make Co/SiO2 catalyst with sol gel method With increasing the amount of oxalic acid and ethanol you will be able to produce catalystr with higher surface area.
This is a very interesting topic. Is there any particular reason for adding Oxalic acid instead of water and synthesis temperature of 70 C?
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