I am trying to impregnate 10wt%Cu-10 wt%Fe on alumina pellets (1/8" in diameter, Alfa Aesar). The procedure I am following right now is mixing the alumina pellets and metal nitrate solutions (copper nitrate and iron (III) nitrate) with a weight of support to the volume of deionised water ratio of 1:5. The solution+support is mixed using a rotavapor for 3 hours and then the pellets are filtered out . Obviously, the filtration method will not ensure the required Cu-Fe loading on the alumina pellets. The problem is that when I mix and rotate the solution+pellets, the color of the solution changes from green to brown (I suspect some reaction of alumina with the metal nitrates). I tried to evaporating the metal precursor solution after impregnation using the rotavapor at 60°C of the water bath temperature (instead of the filtration step), but it led to the deposition of brown residue on the alumina pellets. What suggestions you will have to have an effective impregnation?
The color change may be preferential adsorption of one metal over the other.
Try dry impregnation. Determine the pore volume of the alumina (cc/g). Then carefully and slowly add the volume of the metal solution that matches the weight of the sample. The systems should stay free-flowing (dry).
In impregnation method the preparation process must be in vacuum
Dear Madan Behera, The brown color in the solution is because of formation of iron(iii) nitrate nonahydrate. That's impossible to occur a reaction between the salt and alumina. I think if you calcine the sample at the higher temperature (400 C) the color will be removed.
William G. Borghard : Thank you for your answer. The ultimate goal of the lab-scale synthesis of impregnated sample is to have impregnation at a large scale (around 2 kg) . Do you think dry impregnation (the method you mentioned in your answer) can be feasible for such a large quantity of synthesis?
Ghazwan Saleh Ahmed : Thank you for your answer. With the current apparatus, we are not able to have a vacuum. The only way I can have a vacuum is with the vacuum pump of my rotavapor apparatus. But if I have the vacuum using the pump in the rotavapor, I fear that I will have evaporation taking place (even if the water batch temperature is at 30°C).
Mohammad Reza Toosi : Thank you for your answer. The reaction between alumina and metal salts is not feasible according to me too but I outlined it just as a possibility. With the calcination, I have tried calcining my sample at 400°C, but there was no change in the colour (it is still brown as it was before the calcination). I think as answered by William G. Borghard , the copper probably adsorbs faster than the iron for which we have more iron left in the solution leading to the change in the colour from green to brown (brown probably due to iron nitrate as mentioned by you).
@madanbehera yes, I've seen dry impregnation done at commercial scale many times. You could get a pilot scale batch tolled for demonstration.
Hallo
you may try with organic solvent(Ethanol) to prepare (Copper+Iron(III) Nitrate) for adsorption in alumina and then ethanol to be recovered by rota-vapor connected to vacuum pump and calcined at 400 deg in a nitrogen atmosphere.
The Alumina balls should have a high specific surface area( 200 to 240)m2/gm
A simple process recommended by Balakrushna Padhi would be ore feasible for you to prepare target material.
Based on my experience, when Cu is introduced by the wet impregnation, the solvent elimination using filtration is not sufficient for some supports. However, the rotary evaporator might be used instead. I have also observed the change in color, however, it did not affect the properties of the calcined catalyst.
- Badges
- Science topic
- Similar topics
- Biological Science
- Zoology
- Invertebrate Zoology
- Arthropods
- Insects