What should be my basis in choosing whether excess soution impregnation or incipient wetness impregnation in doping TiO2 with CuO?
Usually the dispersion is higher when the precursor of the active phase is deposited by electrostatic adsorption than by IWI. This is due to the fact that electrostatic adsorption implies a relatively strong interaction between the ionic precursor and the oxide surface. This interaction will reduce sintering during the following steps of the catalyst preparation. For copper on titania, considering the point of zero charge (PZC) of titania (ca. 5), adsorption of a cationic precursor of copper at a slightly acidic pH should give good results.
A drawback of electrostatic adsorption could be that the uptake of the precursor is limited (it may not be the best option if you wnat to achieve high loading). IWI is also easier and less time consuming.
I don't have the required instruments for electrostatic adsorption. I can only use impregnation.
Do you have some articles specifying the required pH for the impregnation? Journals that I've read do not show a slightly acidic environment, only water was used.
Sorry I was probably not clear and made mistake. First it is a basic pH that should be used. Second, you would not need any special equipment for electrostatic adsorption. Electrostatic adsorption is what you would call an impregnation with excess solution. For the adsorption of a cation on an oxide surface, the surface should be negatively charged. In order to get a negative charge on the surface, the pH of the solution should be significantly higher than the PZC of the oxide surface. For titania, it should be several pH units above 5, the PZC of titania. This could be a problem for copper due to the precipitation of Cu(OH)2. Hence, the NH3 complex of copper is used. You can have a look at the article below for more information (it's for copper on silica, not on titania)
Article The synthesis of highly dispersed noble and base metals on s...
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