Generally, we know that the specific surface area decreases after addition of metal. Actually I am working with hydrotalcite support catalyst. I am already add cerium over that support by wet impregnation technique. I already found the specific surface area of the catalyst. The result showed that the specific surface area increased after addition of cerium on the support. Please anyone explain me the reason for this case.
It is possible that Ce can increase the porosity of your material? i'm wondering if Ce can replace some Mg or Al atoms through a galvanic displacement process or corrosion.
The first question to ask is : what was the initial surface area, and what is the final one ? If the increase is low, maybe it is within the uncertainty of the measurement, and is not significant... If there really is an increase, maybe there is no need to invoke a structure change. Generally, surface area decreases because of pore blocking / clogging. If you don't have such effect, either because your pores are too wide or because they are only a low amount of them, then the addition of a new phase at the surface of a substrate should logically create heterogeneity, roughness, and terefore a higher surface area, provided that very small particles were deposited. I don't expect that additional porosity is created, but very small particles shoudl have a higher surface area than the substrate itself.
Alain
Dear Alain and V. Alejandro,
The initial specific surface area before calcination of hydrotalcite support was 1.9 m2/g. After calcination the surface area reduced to 1.5 m2/g. But when I doped cerium on the support, then the surface area increased and it was 5.6 m2/g. After that, when I further increased the amount of cerium, then the surface area reduced to 3.6 m2/g. The pore diameter of the support was 51 nm. After cerium loading the pore diameter reduced to 6.4 and 9.1 nm. Please explain me why it was happened.
The values from the Surface area is too low, maybe you are in the %. I am agree with Ajay Jha, because it is maybe a mistake in the desgassificating process
I assume you have added Ce as oxide, not as metal. Ce oxide has its own surface area that you are measuring in addition to that of hydrotalcite. Very simple.
Pls notice that you have to measure such low surface areas by the flow method, not volumetric.
It depends on the type of metal added and also how the metal is added. If metal or metal oxide added have bigger size than the pores it can increase the surface area to some extent
Have you noticed changes in pore size distribution? May b e micropores turned into measurable mesopores
Dear Raman,
I noticed that in change of pore size distribution. The average pore size of hydrotalcite support is around 50 nm. After impregnation of cerium, the pore size reduced to 20 nm.
Dear Friend! I
You have confirmed my assumption that the application of metal Led to the disclosure of the micropores, which were not available for the adsorption of nitrogen and they became available for nitrogen. I can not understand how it took place, but if we invent something, I'll let you know
Best regards
p
It would be easy to answer specifically if you provide the bare support characteristics along with the extent of metal impregnation.
Dear Sujoy Bepari ...............ofcourse surface area can be increased if the reaction b/w the two metals is galvanic replacement reaction, i don't know which caping agent you are using. if you find out the effect of caping agent you can easily understand the mechainsm of the reaction.
Initial surface area of hydrotalcite is very low, you please repeat the analysis. Have you done XRD for HT. In XRD did you get correct pattern, if not complete layered structure is not formed so you got less surface area.
You have to check for the thermal pretreatment of the specific surface area analysis.
Hydrotalcite phase may have a low thermal stability and can transform upon oxidation (calcination in air) so the porosity could be gretaly affected. Have you checked by TGA the thermal stability of your starting material ?
I think that surface area be constant but the activity of support may be increase or decrease depending on the metal added.
Specific surface area may be increased or decreased by various chemical and/or thermal treatments and of course, during its initial preparation method.
If you want to receive more specific information you yourself have to be more informative about the catalyst itself and its preparation method..
Regards
M. Baerns
There are some ways of enhancing the specific surface area but these usually depend on some sort of corrosive action e.g. by acids. The magnitude of the increase you have measured needs to be considered in relation to expected experimental error which might be as high as 10-15% depending on the methodology used for the area measurement and calculation.
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