Sciencemadness Discussion Board - Synthesis of cerium (IV) salts

Synthesis of cerium (IV) salts

j_sum1 - 18-4-2024 at 03:01

I decided today that one of my next projects will be synthesis of some ceric salts.
For a starting material I have about 200g of off-white CeO2 polishing powder.
Ceric ammonium nitrate is an obvious target. Ceric ammonium sulfate is probably on the list as well. I will likely do ceric nitrate also.

I am still in the early stages of researching. I found 1 nice YT clip of CAN. There is also a thread here by blogfast where he made CAS. And wikipedia hints at some procedures that seem doable. I will add links to these when I am on a proper computer.

The sulfates have negative solubility curves which will make for some interest8ng separations. There are also some extraction possibilities using diethyl ether for some compounds.

One thing I have not stumbled across yet in my reading but will probably attempt is fusing CeO2 with KNO3 - similar to the synthesis of chromates from Cr2O3.

I am interested if anyone has experience or advice with synthesising these salts or who could point me to some reliable references. Of course I will do my own reading, bit it seemed sensible to consult the wealth of information here.

j_sum1 - 18-4-2024 at 16:47

For anyone following...

This thread by garage chemist back in 2007 has a lot of useful discussion.
blogfast25's thread on ceric ammonium sulfate looks like an interesting activity.
Google patent for production of ceric ammonium nitrate.
Brauer beginning at pdf page 1179 has some information that is worth sifting through. Not sure how useful since it seems his starting materials were mixed rare earth ores. There are probably a lot of steps that are not needed. I missed the reduction to cerous salts using hydroquinnone mentioned by garage chemist. That may be elsewhere in Brauer.
chemicaloid's yt video presents a straightforward procedure. I would be looking to reduce the number of steps with days of stirring. But otherwise this seems very accessible.
Other SM discussions here and here with nice work by Lion850

Useful little paper by Frederick Smith PHD
Attachment: cerate oxidimetry - SMITH.pdf (1.7MB)
This file has been downloaded 126 times

As so often happens with this kind of thing, the better information seems to come from this board.
Anyway, I will embark on a bit of reading but will still welcome thoughts and suggestions from anyone who has worked with cerium compounds.

[Edited on 19-4-2024 by j_sum1]

bnull - 18-4-2024 at 20:10

Quote: Originally posted by j_sum1

Brauer beginning at pdf page 1179 has some information that is worth sifting through. Not sure how useful since it seems his starting materials were mixed rare earth ores. There are probably a lot of steps that are not needed. I missed the reduction to cerous salts using hydroquinnone mentioned by garage chemist. That may be elsewhere in Brauer.

I thought for a minute it was p.1179 in the book (saw zirconium and hafnium and thought, "huh?"), and not p.1179 of the pdf. Apparently we're using different readers.

Anyway. The hydroquinone process is described in the next page (1180 in the pdf, 1133 in the book). Page 1203 (1156 in the book) describes the production of generic rare earth sulfates. Here's a snapshot of the paragraphs.

It seems you can use light and alcohol in place of hydroquinone. See the snaphot of the "preparation of cerium(III) sulphate by the photochemical reduction of cerium(IV) compounds with ethanol" from Practical Inorganic Chemistry by Spitsyn, Vorobyova, and Dunaeva.

Inorganic Syntheses--at least the first seven volumes--has nothing (and the other volumes are very uninteresting, honestly).

Blanchard (in the Library), from p.283 onwards, has some preparations of cerium compounds. Attached is a copy of the cerous chloride preparation. It evolves chlorine from the oxidation of hydrochloric acid, so using a sacrificial reducing agent is a sensible idea.
Attachment: Cerous chloride.pdf (251kB)
This file has been downloaded 118 times

Ludwig Vanino's Handbuch der Präparativen Chemie, volume I (inorganic compounds; Internet Archive has a copy), deals with cerium ("Zer") in pages 719 to 729. Cerium ammonium nitrate and cerous sulfate in p.727, ceric sulfate in p.728. I won't include the procedures because there is a big chance you have never seen this book (and volume II, organic compounds) and I would be spoiling your fun. It's in German.

The Library has two other books where you can find more information. The first one is A Text-book of Inorganic Chemistry, volume IV, by H. F. V. Little (who was "Chief Chemist to Thorium, Ltd." in 1917). Detailed preparations of ceric and cerous compounds, and anything in between. The second book is Mellor's A Comprehensive Treatise on Inorganic and Theoretical Chemistry, volume V. Again, preparations of ceric and cerous derivatives.

I hope it helps.

woelen - 19-4-2024 at 00:03

I hope that your oxide CeO2 is not extremely inert. It depends on how strongly it is calcined.

I myself have half a kilo of Nd2O3, and another sample of 100 grams of Nd2O3. I could buy the half kilo of Nd2O3 for cheap. I intended to use it for making other Nd-salts. I had good experience with my smaller sample of (expensive) Nd2O3, which I used to make solutions of Nd2(SO4)3, Nd(NO3)3, and NdCl3 (I have a web page about that), so I decided to scale up things and make nice quantities of Nd-salts with the new cheap Nd2O3.

The Nd2O3 from my 100 gram sample quickly dissolves in moderately concentrated acids (e.g. 10% HCl or 10% H2SO4), even without heating. It dissolves with a soft hissing noise, and production of some heat (the liquid becomes luke-warm, when some of that Nd2O3 is added to the dilute acid).

The Nd2O3 from my half kilo sample, however, has totally different properties. It looks the same, but it is completely insoluble in dilute acids. HCl, HNO3 and H2SO4 have no effect on it. Not even for prolonged boiling. I left it sitting in the acid for days, but even then I only had traces of Nd dissolved in the liquid. I finally gave up with that Nd2O3 and I still have a big bottle of it, unused.

I have read that CeO2 also can be extremely inert, and that quite extreme treatment may be necessary to get it dissolved.

j_sum1 - 19-4-2024 at 02:58

Update.

I have processed a 25g batch of CeO2, stirring it in 20% HCl at 90C while adding H2O2 dropwise over a period of 2 hours. I then let it stir while hot for another 3-4 hours.

It filtered with some difficulty but it seems that more than half the oxide reacted. The filtrate is a light lemon yellow with some turbidity from material that got through the frit. It tests positive for trace amounts of Fe3+ but this can be removed at the next step. I am pretty confident I can get a small batch of ceric ammonium nitrate from what I have. My next attempt will be using sulfuric acid. I think I can get more aggressive reaction conditions that way and hopefully dissolve all of the oxide.

Does anyone have any thoughts about fusing directly with potassium nitrate in a crucible? My thought is that I might end up with a soluble Ce(IV} salt without the prolonged heating and filtering.

And thanks bnull. I did find the hydroquinone step. But I seem to have been successful using peroxide as a reductant. Brauer's challenge seems to have been that he was starting with less pure source material.

bnull - 19-4-2024 at 06:12

Quote: Originally posted by j_sum1

Does anyone have any thoughts about fusing directly with potassium nitrate in a crucible? My thought is that I might end up with a soluble Ce(IV} salt without the prolonged heating and filtering.

Use a mixture of potassium (or sodium) nitrite and nitrate in place of the plain salt. The advantages are the lower melting temperature and the nitrite gets oxidised to nitrate.

Quote: Originally posted by j_sum1

My next attempt will be using sulfuric acid. I think I can get more aggressive reaction conditions that way and hopefully dissolve all of the oxide.

It will probably liberate oxygen when dissolving, and part of the cerium will be reduced to cerous ion. Try sulfuric acid with some reductant in it. Hydrogen peroxide is not so good now since your ceria has iron. Well, ferrous sulfate seems a good choice. Or formaldehyde. And you can precipitate potassium cerium(IV) sulfate as cerium(IV) alum (?) by the addition of potassium chloride (iron will stay in solution as sulfate or chloride or both).

@woelen: You may want to search inside the last three books I mentioned in the post above for something that works with your neodymium oxide. It's way more than a few pages worth of material, with extensive references, and your German is obviously better than mine^*.

*: I'm still trying to learn German and Dutch. And to pronounce "Huygens".

[Edited on 19-4-2024 by bnull]

chornedsnorkack - 19-4-2024 at 12:11

Note that cerium ammonium salts seem to be stable - that is, Ce⁴⁺ does not oxidize NH₄⁺

[Edited on 19-4-2024 by chornedsnorkack]

j_sum1 - 19-4-2024 at 14:24

@ bnull
Melting piont of KNO3 is not a problem. I think I will save my precious nitrite.
Also, the first step in dissolving reduced the Ce to Ce(III). That is what the peroxide (or hydroquinone) is for.
My CeO2 has minimal iron contamination. This is not always the case though. The pink stuff sold as polishing powder gets its colour from iron contamination. That said, I would expect to pick up some contamination from my cast iron crucible. This might be a problem because the iron would normally be removed as a precipitate by pH adjustment of the Ce3+ solution before oxidation. Another method would be needed if it was Ce4+.

@chornedsnorkack
It does seem that ammonium salts are quite stable. I have seen references to sodium and potassium salts as well.
I find the structure of the nitrate complex fascinating and I suspect it goes a long way to stabilising the Ce4+ ion.

More to do today. I should have some product by the end.

bnull - 19-4-2024 at 17:25

The problem with using pure potassium nitrate is that, differently from chromium, cerium doesn't form anions. You need something to take up the oxygen from cerium while giving it a soluble anion in exchange (which I hadn't thought of before). Sodium or potassium bisulfate could work, if it wasn't for the possibility of nitric acid vaporising from the mixture.

My reason to discard hydrogen peroxide was because it is both a reductant and an oxidiser. It acts funny in the presence of manganese dioxide, maybe the same could happen with cerium(III).

As for the iron contamination, addition of potassium chloride (not sulfate) to the solution containing cerium(IV) and iron in the presence of sulfate ions will precipitate potassium cerium(IV) sulfate while iron stays in solution. Potassium cerium(IV) sulfate is less soluble than potassium iron sulfate (I managed to lose the reference for that; Mellor or Little or Blanchard, it was one of them). Oxidise first and worry about the iron later, it's just traces anyway.

[Edited on 20-4-2024 by bnull]

j_sum1 - 19-4-2024 at 18:00

Peroxide and cerium seems pretty controllable.
Ce3+ oxidation in alkali, Ce4+ reduction in acid. I don't know how this is affected by the presence of other cations, but I am not encountering any problems yet.

Good point on the absence of cerium oxyanions. I will play with a couple of ideas but not invest any reagents on the fusion pricess if it looks like a dead end.

As for getting rid of iron...
Chemicaloid's video deals with it when it is present in the cerous solution directly after dissolving and filtering CeO2. He adjusted the pH to between 2 and 4 to selectively precipitate iron hydroxide. I did the same and got rid of a small amount, but I could still detect Fe3+ in the filtrate. It is a small impurity so I am not concerned. Brauer has a method for obtaining ultra pure CeO2 if I was really worried. For me, that is a backward step and not worth the effort.

j_sum1 - 19-4-2024 at 18:05

By the way. Can anyone explain the colour of Ce(IV)?
This came up in one of the treads I linked above but did not get a clear answer.
I would expect Ce to behave like Ti where the 3+ ion may be coloured and the 4+ ion is clear. Is the effect entirely due to complexing? I notice that CeO2 os colourless when pure enough.

bnull - 20-4-2024 at 06:07

I suspect that @12AX7 was in the right path. The paper Cerium(iv) complexes with guanidinate ligands: intense colors and anomalous electronic structures by Yusen Qiao et al. may give you some answers. The third paragraph of the Introduction begins thus:

Quote:

With respect to cerium(iv) complexes, their intense colors are primarily due to parity-allowed ligand-to-metal charge transfer (LMCT) transitions of the Ce⁴⁺ cation.

These transfers involve the orbital 4f. The Ce⁴⁺ coordination compounds are yellow with H₂O and orange with NH₄⁺ because of the transfers.

[Edited on 20-4-2024 by bnull]

j_sum1 - 21-4-2024 at 19:52

And.....

I managed to reduce the lot to Ce3+ somehow.
I now have a flask with a crystal clear solution containing 95 mmol of cerium.
Something to sort out next weekend I suppose.

Texium - 22-4-2024 at 06:09

Titanium(IV) is also capable of forming bright orange LMCT complexes under some conditions: https://youtu.be/-J-ME6QBMCE?si=NwMhB4BfKtTrl4SI

So I think that’s right on the money

clearly_not_atara - 22-4-2024 at 06:11

Cerium (IV) chloride is not stable; a few seconds of Google indicates that solutions of CeCl4 slowly decompose. So dissolving CeO2 in HCl would seem to be unacceptable, and it's possible that your attempt with peroxide and HCl gave CeCl3.

It would be nice to dissolve it in some kind of inert acid. Perchloric acid is common in the old papers. Toluenesulfonic acid probably works. I have a suspicion that pyroglutamic acid could dissolve CeO2, but it might form a complex that doesn't easily dissociate, instead of the desired nitrato-complex. Most of the common organic acids are too weak or will be oxidized under the conditions.

It is curious that the ion Ce(NO3)6(2-) is formed. Nitrate is usually a weak ligand. Unfortunately, this suggests that Ce4+ might complex with lots of other things as well, which could make it difficult to obtain the nitrate complex salt. But maybe it just has a high affinity for nitrate?

Am I correct in reading this project as "I want to make (NH3)2Ce(NO3)6, but I don't want to use lots of nitric acid, so I'm trying to dissolve Ce4+ and precipitate with NH4NO3"?

[Edited on 22-4-2024 by clearly_not_atara]

bnull - 22-4-2024 at 11:46

Quote: Originally posted by clearly_not_atara

Cerium (IV) chloride is not stable; a few seconds of Google indicates that solutions of CeCl4 slowly decompose. So dissolving CeO2 in HCl would seem to be unacceptable, and it's possible that your attempt with peroxide and HCl gave CeCl3.

You just have to take into account why cerium(IV) chloride is unstable: it oxidises chloride to chlorine and is reduced to cerium(III) chloride. From Mellor, volume IV, p.393:

The standard electrode potential of chlorine to chloride is +1.36 V, lower than the potential of ceric to cerous ion, which is +1.61 V. The conversion from Ce(IV) to Ce(III) with the use of a reductant is the way to dissolve ceria in acids.

Quote: Originally posted by clearly_not_atara

Am I correct in reading this project as "I want to make (NH3)2Ce(NO3)6, but I don't want to use lots of nitric acid, so I'm trying to dissolve Ce4+ and precipitate with NH4NO3"?

From Vanino, volume I, p.725, third paragraph under "Zerdioxyd" (cerium dioxide):

Quote:

Pure calcined cerium oxide is completely insoluble in hydrochloric and nitric acid; it is attacked in the presence of reducing agents, such as hydrogen iodide, by boiling with hydrochloric acid and ammonium iodide, nitric acid and hydrogen peroxide, hydrochloric acid and tin chloride.

Cerium(III) in solution can be oxidised back to cerium(IV) by persulfate. From there you can make any ceric salt you want. Quite good, eh?

Quote: Originally posted by clearly_not_atara

It would be nice to dissolve it in some kind of inert acid. Perchloric acid is common in the old papers. Toluenesulfonic acid probably works. I have a suspicion that pyroglutamic acid could dissolve CeO2, but it might form a complex that doesn't easily dissociate, instead of the desired nitrato-complex. Most of the common organic acids are too weak or will be oxidized under the conditions.

Cerium(IV) is an oxidiser as good as potassium permanganate. If p-toluenesulfonic acid is oxidised by permanganate (see Donald G. Lee and Brian E. Singer, "Oxidation of hydrocarbons. II. Kinetics of the oxidation of p-toluenesulfonic acid by potassium permanganate"), the same will probably happen with cerium(IV).

It would be interesting to see if pyroglutamic acid can handle it (I'll save that for later; thank you very much for the idea).

Quote: Originally posted by clearly_not_atara

It is curious that the ion Ce(NO3)6(2-) is formed. Nitrate is usually a weak ligand. Unfortunately, this suggests that Ce4+ might complex with lots of other things as well, which could make it difficult to obtain the nitrate complex salt. But maybe it just has a high affinity for nitrate?

It seems to have affinity for any ligand whatsoever, as long as the ligand is not easily oxidisable.

[Edited on 22-4-2024 by bnull]

[Edited on 22-4-2024 by bnull]

Texium - 22-4-2024 at 12:41

I have quite a lot of CAN and CAS and a smaller amount of cerium(IV) sulfate I'd be happy to play with if any comparative experiments need to be run. I'm also selling CAN and CAS, though I'm not sure if I'd feel comfortable shipping strong oxidizers overseas.

bnull - 22-4-2024 at 15:46

@Texium: Since you volunteered, could you please verify if p-toluenesulfonic acid is oxidised by cerium(IV)? I found an experiment [1] in which cerium(IV) p-toluenesulfonate, made in situ by oxidation of the cerium(III) salt, was used as oxidiser. What they didn't mention was if the tosylate anion was unaffected during the course of the operation or if it suffered any losses.

Another sulfonic acid that seems interesting is methanesulfonic acid. As described in [2], methanesulfonic acid solubilizes both cerium(III) and cerium(IV). A combination of this acid with hydrogen peroxide or another reductant seems a viable alternative, since access to mineral acids may be a problem for many home chemists.

[1] F. L. S. Purgato, J. R. Romero. Electrooxidation of Hydroxyl Compounds Using Cerium Salts as Mediators: The Importance of Substrate Size for Catalyst Regeneration. https://www.sciencedirect.com/science/article/abs/pii/S00219...

[2] R. M. Spotnitz, R. P. Kreh, J. T. Lundquist, P. J. Press. Mediated Electrosynthesis with Cerium(IV) in Methanesulphonic Acid. https://link.springer.com/article/10.1007/BF01033596

[Edited on 23-4-2024 by bnull]

j_sum1 - 22-4-2024 at 16:14

I am on new territory here and appreciate all the input.

As a first run i have followed the procedure illustrated by chemicaloid in his video. (Link above).
A couple of things stand out from his procedure.

long stirring and reaction times. I am not convinced that this is entirely necessary for all steps.

a need to control temperature and pH during these reactions. Always a challenge if you don't want to babysit the reaction.

H2O2 is used as both an oxidant and a reducer at different times. This is controlled by adjusting the pH. Alkaline conditions cause oxidation.

It is entirely possible that my failure results from not managing the reaction as well as he did. However, I note that he seemed to have had no problem with chloride ions. My instinct was to go with sulfuric acid but I decided to simply copy him on this first run.

I am not 100% sure I obtained Ce(OH)4 in the process. My colour was a bit different from the video. There could easily have been some Ce(OH)3 at this step.
On adding nitric acid there was an immediate colour change indicating Ce4+ species, but it did not get as dark as the video. I was not at precisely the same temperature. Addition of NH4NO3 to form the ammonia salt did not seem to work. I think that is when reduction occurred.
I was using the same excess ratios for HNO3 and NH4OH as the video rather than the more conservative amounts i calculated. Next attempt I will dial it back.

I now have a clear solution which has no iron present. The plan is to distil off the nitric acid (may as well save it). And then to dry it out which should give me a very workable sample of ceric or cerous oxide or hydroxide to start again.

j_sum1 - 22-4-2024 at 16:20

I have plenty of sulfuric and nitric acid at present. Normally I try to be conservative with these as they are not always easy to obtain. But I have not been holding back for this project. I am not looking at any sulfonic acid routes at this stage nor am I likely to.

It did occur to me that this might be a synthesis that could be adapted for almost 100% OTC reagents. I may turn my attention in that direction a bit later. Polishing powder is certainly cheap enough and the product has enough interesting uses that this could be a really useful exercise.

bnull - 23-4-2024 at 06:19

@j_sum1: Some ideas you may apply in the process:

cerous sulfate is insoluble in saturated solutions of alkaline and ammonium sulfates;
precipitation of cerous hydroxide from solutions is inhibited by glycerol (https://archive.org/details/sim_zeitschrift-fuer-anorganisch...);
precipitation of cerous hydroxide from solutions by ammonium hydroxide is incomplete and slow in the presence of ammonium acetate;
potassium cerium sulfate^* is sparingly soluble in cold solutions of saturated potassium sulfate.

A possible OTC process: cerium is dissolved as cerous ion by reduction of ceric oxide with ferrous sulfate (maybe even scrap iron) in 30% sulfuric acid (lead battery solution). Neutralise the excess acid with potassium or sodium hydroxide. The solution is aerated before, during, and after neutralization to convert ferrous to ferric. When the solution is cool, add more base until the first sign of precipitation. Then add glycerol and correct the pH to 7 or higher. Filter of the ferric hydroxide and adjust the pH to about 7. Add a calculated amount of potassium sulfate (fertilizer) or chloride (salt substitute) to the solution to saturate it with relation to potassium sulfate and precipitate the double sulfate.

*: I forgot which one it is, if cerious or ceric. It is in Mellor's IV.[\size]

[Edited on 23-4-2024 by bnull]

Lion850 - 3-5-2024 at 22:09

I found that the best way to dissolve 'inert' CeO2 was with hot sulphuric acid. This should be the link to my report:

https://www.sciencemadness.org/talk/viewthread.php?tid=15508...

maldi-tof - 12-5-2024 at 12:20

The easier one is the cerium (iv) and ammonium sulphate 2-hydrate.
It cristalyzes quite easily.
The other cerium (iv) salts I tried before, I never reached an assay higher than 98,5%.