Palladium(II) oxide
Encyclopedia
Palladium oxide is the inorganic compound
of formula Pd
O
. It is the only well characterised oxide of palladium. It is prepared by treating the metal with oxygen. Above about 900 °C, the oxide reverts to Pd metal. It is not attacked by acids. As palladium is an unreactive metal, palladium oxide is difficult to produce and decomposes relatively easily.
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
,
or the product of dissolving palladium in aqua regia
, followed by the addition of sodium nitrate at 600 °C. 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.nH2O can be produced as a dark-yellow precipitate by adding alkali to a solution of palladium nitrate, Pd(NO3)2.
.
Inorganic compound
Inorganic compounds have traditionally been considered to be of inanimate, non-biological origin. In contrast, organic compounds have an explicit biological origin. However, over the past century, the classification of inorganic vs organic compounds has become less important to scientists,...
of formula Pd
Palladium
Palladium is a chemical element with the chemical symbol Pd and an atomic number of 46. It is a rare and lustrous silvery-white metal discovered in 1803 by William Hyde Wollaston. He named it after the asteroid Pallas, which was itself named after the epithet of the Greek goddess Athena, acquired...
O
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
. It is the only well characterised oxide of palladium. It is prepared by treating the metal with oxygen. Above about 900 °C, the oxide reverts to Pd metal. It is not attacked by acids. As palladium is an unreactive metal, palladium oxide is difficult to produce and decomposes relatively easily.
Preparation
PdO is often obtained as a poorly defined material that is generated for applications as a catalyst (see Adams catalyst). Palladium oxide is prepared by heating palladium sponge 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
Palladium chloride, also known as palladium dichloride, are the chemical compounds with the formula PdCl2. PdCl2 is a common starting material in palladium chemistry – palladium-based catalysts are of particular value in organic synthesis. It is prepared by chlorination of...
and potassium nitrate
Potassium nitrate
Potassium nitrate is a chemical compound with the formula KNO3. It is an ionic salt of potassium ions K+ and nitrate ions NO3−.It occurs as a mineral niter and is a natural solid source of nitrogen. Its common names include saltpetre , from medieval Latin sal petræ: "stone salt" or possibly "Salt...
,
- 2 PdCl2 + 4 KNO3 → 2 PdO + 4 KCl + 2 NO2 + O2 (possible reaction)
or the product of dissolving palladium in aqua regia
Aqua regia
Aqua regia or aqua regis is a highly corrosive mixture of acids, fuming yellow or red solution, also called nitro-hydrochloric acid. The mixture is formed by freshly mixing concentrated nitric acid and hydrochloric acid, usually in a volume ratio of 1:3, respectively...
, followed by the addition of sodium nitrate at 600 °C. 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.nH2O 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 in organic synthesisOrganic synthesis
Organic synthesis is a special branch of chemical synthesis and is concerned with the construction of organic compounds via organic reactions. Organic molecules can often contain a higher level of complexity compared to purely inorganic compounds, so the synthesis of organic compounds has...
.