Palladium(II) oxide
Palladium(II) oxide is the inorganic compound of formula PdO. It is the only well characterised oxide of palladium.[1] 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.[1]
 | |
| Names | |
|---|---|
| Other names
Palladium monoxide | |
| Identifiers | |
3D model (JSmol) |
|
| ChemSpider | |
| ECHA InfoCard | 100.013.836 |
PubChem CID |
|
| UNII | |
CompTox Dashboard (EPA) |
|
| |
| |
| Properties | |
| PdO | |
| Molar mass | 122.42 g/mol |
| Appearance | greenish-black powder |
| Density | 8.3 g/cm3 |
| Melting point | 750 °C (1,380 °F; 1,020 K) decomposes |
| insoluble | |
| Solubility | insoluble in acid slightly soluble in aqua regia |
| Hazards | |
| Flash point | Non-flammable |
| Related compounds | |
Other anions |
Palladium sulfide |
Other cations |
Nickel(II) oxide |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references | |
Structure
The structure of PdO is tetragonal (P42/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.[2] 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 + 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 and potassium nitrate,
- 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 at 600 °C.[3][4] 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, PdO.nH2O can be produced as a dark-yellow precipitate by adding alkali to a solution of palladium nitrate, Pd(NO3)2.[1]
Applications
Materials called palladium oxide are useful catalysts for catalytic hydrogenation in organic synthesis.[3]
References
- Greenwood, Norman N.; Earnshaw, Alan (1984). Chemistry of the Elements. Oxford: Pergamon Press. pp. 1336–37. ISBN 978-0-08-022057-4.
- Dwight, P.H. (1990). "Preparation and Properties of the System CuxPd1-xO (0<=x<=0.175)". J. Solid State Chem. 86: 175. doi:10.1016/0022-4596(90)90132-H.
- Donald Starr and R. M. Hixon (1943). "Tetrahydrofuran". Organic Syntheses.; Collective Volume, vol. 2, p. 566
- Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1965, NY. Vol. 2. p. 1583.