Palladium(II) oxide is the
inorganic compound of formula
Pd O. It is the only well characterised oxide of
palladium
Palladium is a chemical element with the symbol Pd and atomic number 46. It is a rare and lustrous silvery-white metal discovered in 1803 by the English chemist William Hyde Wollaston. He named it after the asteroid Pallas, which was itself na ...
.
It is prepared by treating the metal with oxygen. Above about 900 °C, the oxide reverts to palladium metal and oxygen gas. It is not attacked by acids.
Structure
The structure of PdO is tetragonal (''P''42/''mmc'') ''a'' = 3.044, ''c'' = 5.328 Å. The Pd atoms are square planar as expected for a d
8 metal ion and the oxygen atoms are approximately tetrahedral. The closest Pd–Pd distance is 3.044 Å and is almost within the range which can be considered a bonding distance.
Preparation
PdO is often obtained as a poorly defined material that is generated for applications as a catalyst. Palladium oxide is prepared by heating palladium
sponge metal in oxygen at 350 °C.
:2 Pd + O
2 → 2 PdO
The oxide is obtained as a black powder. The oxide also may be prepared specially for catalytic use by heating variously a mixture of
palladium(II) chloride
Palladium(II) chloride, also known as palladium dichloride and palladous chloride, are the chemical compounds with the formula PdCl2. PdCl2 is a common starting material in palladium chemistry – palladium-based catalysts are of particular value ...
and
potassium nitrate
Potassium nitrate is a chemical compound with the chemical formula . This alkali metal nitrate salt is also known as Indian saltpetre (large deposits of which were historically mined in India). It is an ionic salt of potassium ions K+ and nitr ...
,
: 2 PdCl
2 + 4 KNO
3 → 2 PdO + 4 KCl + 4 NO
2 + O
2 (possible reaction)
or the product of dissolving palladium in
aqua regia, followed by the addition of
sodium nitrate at 600 °C.
[Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1965, NY. Vol. 2. p. 1583.] A hydrated form of the oxide (which dissolves in acid) can be prepared by precipitation from solution, for example, by hydrolysis of palladium nitrate or reaction of a soluble palladium compound with a strong base. The brown hydrated oxide converts to black anhydrous oxide on heating. Its susceptibility to attack by acids decreases at lower water content.
The hydrated oxide (hydroxide), PdO
.''n''H
2O can be produced as a dark-yellow precipitate by adding alkali to a solution of
palladium nitrate, Pd(NO
3)
2.
Applications
Materials called palladium oxide are useful catalysts for
catalytic hydrogenation
Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to reduce or saturate organic ...
in
organic synthesis.
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]
References
Palladium compounds
Transition metal oxides
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