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Chemical Stability and Compatibility - Is HF needed to stabilize molybdenum (Mo)?

 
We are currently reviewing our methods for determining Mo in hydroproccesing catalysts. Our hot plate digestion involves dissolving the catalyst in 10 mls of concentrated H2SO4 and diluting to 500 ml. Our final concentration of Mo is about 70 ppm in solution. Should we be adding a source of F- to stabilize Mo?
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The need for a complexing ligand like fluoride to stabilize Mo in acidic solutions decreases at lower Mo concentrations. We routinely prepare Mo standards in mineral acids (usually HNO3) at concentrations of 100 ppm or lower, do not add HF or any other stabilizer, and have not observed Mo stability issues. Our expectation is that 70 ppm Mo in 2% (v/v) H2SO4 will be stable, though we would recommend creating an artificial 100 ppm Mo solution in that matrix and periodically checking it to verify.

Posted: 08/30/18 23:18:59

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