# My first experience with autocatalysts



## rucito (Dec 3, 2011)

Hi all!
This is my first experience with autocatalysts and platinum
I put a piece of 50 grams in 250ml glass
Cover with HCl to 150ml mark, added 10ml HNO3
and it started to heat up.
Initially the solution was a yellow but later became light brown.
After 2 hours boiling I decided to do a test with SnCl (tested on an old filter) - the result was hardly noticeable.
when the solution cooled yellow color returned.
My question is:
Is this normal color change and low test result?


----------



## Joeforbes (Dec 3, 2011)

Yes, the color change is normal.

50g of catalyst might have 0.1 grams of PGMS (probably less). You've used enough AR for about 10 grams, so 100x as much as you needed. The solution is going to be EXTREMELY dilute, and have a very weak test result.


----------



## skippy (Dec 3, 2011)

50 grams in 160 mL isn't that dillute, 50 grams of catalyst will take up a good bit of space. In my experience it takes very little pgm to add a hue to the water. Yellow suggests to me weakly loaded catalyst.

If you were stannous testing a solution with a lot of free nitric acid in it and especially with not much pgm, your stannous test will be unreliable. Evaporate a tiny sample of your solution down,add hcl, evaporate it down again and then stannous test it. 

I wonder about the color change myself, I've seen it before too. You add oxidizer and you get a really nice strong looking colour that makes you think your solution is getting lots of values in it, but the colour changes after a while like you say. I'm inclined to attribute it to cerium, a common part of the washcoat. Cerium (iv) cations have a brown colour when in solution, and cerium (ii) is colourless. So maybe the nitric acid oxidizes the cerium to the (iv) state, but the color is lost as the cerium (iv) is reduced from oxidizing HCl.
I've roasted catalyst with sulfuric, and the resulting solution was brown, but negative for palladium. When HCl was added the color disapeered shortly, and chlorine was as a result of the addition.


----------



## Joeforbes (Dec 3, 2011)

skippy said:


> 50 grams in 160 mL isn't that dillute, 50 grams of catalyst will take up a good bit of space. In my experience it takes very little pgm to add a hue to the water. Yellow suggests to me weakly loaded catalyst.
> 
> If you were stannous testing a solution with a lot of free nitric acid in it and especially with not much pgm, your stannous test will be unreliable. Evaporate a tiny sample of your solution down,add hcl, evaporate it down again and then stannous test it.
> 
> ...



The 50 grams would fill most of that acid by volume, but the dissolved PGM solution will be extremely dilute by concentration.


----------



## rucito (Dec 4, 2011)

Thank you for your responses - very helpful and help me understand what's going on!
I think skippy is right and HNO3 is the reason for the weak test rather than concentration.
I have remained almost colorless solution of working with capacitors and SnCl still shows Pd.
Thank you again!


----------



## Joeforbes (Dec 4, 2011)

You have at most 0.2g of PGMs in 160ml of solution. That's about 0.005% concentrated. 

HNO3 would effect the reaction, but it wont have much of one to begin with.


----------



## skippy (Dec 4, 2011)

Joe, if you dissolve 0.2 grams of Pt or Pd in 160mL, it's not very concentrated, but it will still give a very strong stannous test.

Also Joe on your math 100 * 0.2/160.2 = 0.125% (or thereabouts) I live in constant terror of making math errors, so I tend to spot them instinctively. 

Rucito, your catalyst is likely quite poorly loaded. Even without the nitric presence the stannous result would be weak. Maybe that's the sort of material that is used in your country though.


----------

