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Topic: Any experts in synthesis of supported catalysts?  (Read 110 times)

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Offline zuiichi

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Any experts in synthesis of supported catalysts?
« on: May 07, 2021, 11:20:44 AM »
Hi everyone,

I have started a postdoc in heterogeneous chemistry and am facing some issues. As my background is organic synthesis/physical organic chemistry/nanoparticle chemistry, there are a few (trivial?) questions for which I don't find an answer. (BTW, I can't really ask my group as I am the only researcher in it  ::) ) If anyone knows an expert in the field who would be willing to answer just a few questions of have a quick PM exchange, feel free to let them know they can contact me.

Otherwise, if you are an expert yourself, maybe you could help me with the following questions.

Context: I am trying to prepare a few alumina-supported catalysts. However, I have literally never done anything similar.

Questions:

1. My supported catalysts are not active at all! I prepared my samples by wetness impregnation by dissolving either Re2O7 or K2CO3 in an excess of water, to which I added alumina. After mixing and slowly evaporating (over several hours) I obtained a solid that I calcined at 500 °C and 700 °C respectively. The ramp rate was not mentioned in papers. Is there a standard or rule of thumb to follow? I used 10 °C/min and 15 °C/ min. The resulting samples are not catalytically active (tested under published conditions, nothing new here). Can the atmosphere (air or N2) be important during the calcination? Can the ramp rate have an impact? If the procedure requires 2 hours at 500 °C and the ramp rate is slow then the catalyst will be calcined for longer, that's why I sped it up.

2. In the case of the supported K2CO3 catalyst, if the calcination was performed in air, an activation step in N2 at 500 °C is necessary. However, in my case, this does not improve the catalytic activity. Is this something typically required for supported catalysts?

3. What can be the difference between incipient wetness impregnation and wetness impregnation? I tried to measured the amount of water needed to saturate the pores of a known mass of alumina but regardless of how hard I try, the wet alumina separates from the dry why, creates cracks preventing the water to homogeneously wet all the sample. Is there a typical method to follow? I tried sonicating and applying pressure to force the water to reach dry alumina but it was vain. I am afraid that following my method, most of the active species deposited on the surface of the support instead of in the pores and was lost during the calcination.

4. As a new researcher in the field, are there any other parameters/aspects of the synthesis of supported catalysts or preparation for catalysis that people (and maybe me) tend to neglect/not think about?

5. It seems that when a compound is supported, its reactivity is completely different from when it is dissolved. What causes this change?

Thanks in advance! I hope I posted in the correct section of the forum. If not, could a moderator move it in the correct section, please?

zuiichi

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