Adams’ catalyst

What is Adams’ catalyst?

Platinum dioxide, O=Pt=O, also referred to as Adams’ catalyst, is a commonly used catalyst for hydrogenation and hydrogenolysis in organic synthesis. It is typically denoted as PtO2·H2O and is available as a dark brown powder.

Although the PtO2·H2O in its initial state is not a competent catalyst, it can become active by exposure to hydrogen, leading to the formation of platinum black. This platinum black is responsible for catalyzing various reactions.

Preparation

Adams’ catalyst, which can be obtained from chloroplatinic acid H2PtCl6 or ammonium chloroplatinate (NH4)2PtCl6, is prepared by fusion with sodium nitrate.

This preparation method was initially described by Voorhees and Adams. In this process, platinum nitrate is first prepared and then heated to eliminate nitrogen oxides.

The chemical reaction involved in this process is as follows:

Preparation of Adams' catalyst
Preparation of Adams’ catalyst

The resulting brown substance is washed with water to remove any nitrates. The catalyst can be used immediately or dried and stored in a desiccator for later use.

If the catalyst is spent, platinum can be recovered by transforming it into ammonium chloroplatinate using aqua regia (oxidative mixture of 3 parts concentrated hydrochloric acid HCl) and 1 part concentrated nitric acid HNO3) followed by ammonia.

References

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