Palladium(II) oxide is the

inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemist ...

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 d⁸ 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 Regular foamed aluminium A metal foam is a cellular structure consisting of a solid metal (frequently aluminium) with gas-filled pores comprising a large portion of the volume. The pores can be sealed (closed-cell foam) or interconnected (open-c ...

in oxygen at 350 °C. :2 Pd + O₂ → 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 nitrat ...

, : 2 PdCl₂ + 4 KNO₃ → 2 PdO + 4 KCl + 4 NO₂ + O₂ (possible reaction) or the product of dissolving palladium in aqua regia, followed by the addition of

sodium nitrate Sodium nitrate is the chemical compound with the formula . This alkali metal nitrate salt is also known as Chile saltpeter (large deposits of which were historically mined in Chile) to distinguish it from ordinary saltpeter, potassium nitrate. T ...

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''H₂O can be produced as a dark-yellow precipitate by adding alkali to a solution of palladium nitrate, Pd(NO₃)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 co ...

organic synthesis Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...

References

Palladium compounds Transition metal oxides {{inorganic-compound-stub