I've been doing an oxidative catalytic decomposition of liquid formaldehyde at room temperature using hydroxyapatite-dendrimer-Pt nanocomposite as the catalyst. The initial concentration of formaldehyde is 10 ppm (is it too low?) and it takes at least 24 hours to decompose the formaldehyde to zero. I often got unstable result data (can't be reproducible).
The only assumed reaction is formaldehyde + oxygen -> carbon dioxide + water vapour.
Also, the formaldehyde stock solution has some 5% methanol as a stabilizer.
I use a close system in a 250-ml reactor, consist of 25 ml of 10-ppm formaldehyde solution, 0.5 mg powder catalyst, and the remaining is 225 ml of atmospheric air.
Actually an oxidation purpose is needed to maintain the flow rate of oxygen. I feel it is very high loading of your atmospheric air. In oxidation process the oxygen must have residing time to contact with formaldehyde. Let I want to know what temperature is maintained your fixed bed reactor. The main reason of unstable results of your data is not fit in correct way of handling your reactor setup condition. Please try to use the aerator for air flow rate at 10-15 ml / min and the reactant of a feed we can supply may not provide any problem. I suspect Pt is generate more water in your reaction. I also expect the same result you will get in absence of catalyst.
Thank you so much for your kind reply, Mr. Haran..
So, you're saying that the system needs to use an oxygen/air supply, aren't you?
I use room temperature for the process..
However, I've got interesting results.. Without catalyst, only hydroxyapatite (HA), and only Pt-encapsulated G4-PAMAM dendrimer (G4(Pt)) are not working, but with hydroxyapatite-dendrimer-Pt (HA-G4(Pt)) is working (formaldehyde is decomposed to zero, but takes time like the image below)..
Actually, the reactor that I use is only a simple 250-ml volumetric flask.. Is this okay??
No problem Fan, You almost welcome. I mistook about your reaction setup, leave the air flow rates. In your catalytic reactions particle size of Pt atoms contributes various efficient on the oxidative product. The size may depend on specific plane actively play a part of your catalyst. As you reporting HA-G4 (pt) is working comparatively G4-PAMAM and (HA). The working function of such specific catalyst attributed by dentrimers encapsulated surrounding the catalyst enhancing selective and specific reaction coordinates . It is common practice many of previous workers has been carried out. In your case the amount of 10 ppm formaldehyde solution may carrying out 35 h to zero mean we can improve the amount of catalyst 0.1 -0.5% of Pt in HA-G4 quantities. In addition with try this 5 % of tertary butoxide or peroxide derivatives in addition with methanol, from that we can check any alteration of kinetics in your reactions. Please also check the reaction up to 40-50 C in 250/300 ml volumetric flask and if you can please try this different metals Pd, Zn, Mn, V and Ce ions. Check the results if anything will be beneficial we can try to think Pt activity on latter. thank you.
Thank you so much for your suggestions..
So you mean that the supply of oxygen in my system is enough then?? and the problem is in the particle size??
If the particle size is the problem, I think it also makes sense since when I pour the catalyst powder into the system, I usually didn't pay attention to the sizes of the particle (as I recall now, sometimes I use 1mm particle size tops and sometimes it's really small-size powders).. Maybe that's why sometimes I got the result (with HA-G4(Pt) samples) varily, sometimes it decomposes even faster in 17 hours or 24 hours..
The percentage of Pt in my samples is around 10% (by TGA)..
The 5% methanol as the stabilizer in the formaldehyde stock solution is originally included by the manufacturer as I bought it..
I have checked the reaction with 40 C and 75 C, and 75 C results in a slightly faster decomposition rate (in 30 hours to zero, twice checked), but not for 40 C.. I will check again for 40C..
I wish that I could get faster decomposition rate (such as in 1 or 2 h turn to zero) and I would like to try to increase the initial concentration to 100 or 1000 ppm since I think the decomposition rate is affected by the reactant concentration, is it possible??
We guess it is possible by adding the peroxide initiators for rapid oxidative decompose, but dosent know the exact results expect in experimental reports. The % of pt loading thats we need to optimized the reaction concentration in ppm with turn over numnber (TON). Hope you will get better results.
sure I guess,many aerobic oxidations do happen in open air too and only thing you have to ensure is that the solvent does nt evaporate
The fomaldehyde can be oxidised using suitable oxidising agent &also oxidation rate can be increased by using catalyst
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