Important Palladium Chemical Information
Chemical name Formula CAS #
Palladium Pd 7440-05-3
Ammonium hexachloro-palladate(IV) (NH4)2PdCl6 19168-23-1
Ammonium tetrachloro-palladate(II) (NH4)2PdCl4 13820-40-1
Bis(1,5-diphenyl-1,4-pentadien-3-one) palladium(0)
Synonym: Bis(dibenzylidene-acetone) palladium
Pd(C17H14O)2 32005-36-0
Bis(2,4-pentanedionato) palladium(II)
Synonym: Bis(acetylacetonato) palladium(II)
Pd(C5H7O2)2 14024-61-4
cis-Diamminedichloro-palladium(II)
Synonym: Chloropalladosamine
(NH3)2PdCl2 14323-43-4
trans-Diamminedichloro-palladium(II) (NH3)2PdCl2 13782-33-7
Diamminedinitro-palladium(II) Pd(NO3)2(NH3)2 not available
trans-Dichlorobis-(triphenylphosphine) palladium(II) [(C6H5)3P]2PdCl2 13965-03-2
Dichloro(1,5-cyclooctadiene) palladium(II) PdCl2(C8H12) 12107-56-1
Hydrogen tetrachloro-palladate(II)
Synonym: Tetrachloropalladous acid
H2PdCl4 16970-55-1
Palladium(II) acetate
Synonym: Palladium diacetate
Pd(CH3COO)2 3375-31-3
Palladium(II) chloride
Synonym: Palladous chloride Palladium dichloride
PdCl2 7647-10-1
Palladium(II) iodide
Synonym: Palladous iodide
PdI2 7790-38-7
Palladium(II) nitrate
Synonym: Palladous nitrate
Pd(NO3)2 10102-05-3
Palladium(II) oxide
Synonym: Palladium monoxide
PdO 1314-08-5
Palladium(II) sulfate
Synonym: Palladous sulfate
PdSO4 13566-03-5
Potassium hexachloro-palladate(IV) K2PdCl6 16919-73-6
Potassium tetrachloro-palladate(II)
Synonym: Potassium palladium chloride
K2PdCl4 10025-98-6
Sodium tetrachloro-palladate(II) Na2PdCl43H2O 13820-53-6
Tetraammine palladium(II) chloride
Synonym: Tetraammine palladium(II) dichloride
[Pd(NH3)4]Cl2 13815-17-3
Tetraammine palladium hydrogen carbonate
Synonym: TPdHC Tetramminepalladium hydrogen carbonate
[Pd(NH3)4](HCO3)2 134620-00-1
Tetrakis(triphenylphosphine) palladium(0) Pd[(C6H5)3P]4 14221-01-3

Physical and chemical properties of selected palladium compounds

Chemical name Appearance Mass % Pd Melting point °C Solubility in water Solubility in other solvents
Bis(acetylacetonato) palladium(II) yellow crystals 304.64 34.9      
Bis(dibenzylidene-acetone) palladium(0) purple powder 575.02 18.5      
Diamminedinitropalladium(II) yellow 232.5 45.8   slightly soluble soluble in ammonium hydroxide
Dichloro(1,5-cyclooctadiene) palladium(II) yellow crystals 285.51 37.3      
Palladium(II) chloride rust colour powder 177.33 60 675 or 501b (dec.) soluble soluble in hydrochloric acid, alcohol, acetone
Palladium(II) acetate reddish-brown crystals 224.51 47.4 200
(dec.)
insoluble soluble in hydrochloric acid or potassium iodide solution
Palladium(II) iodide black powder 360.21 29.5 350
(dec.)
insoluble soluble in potassium iodide solution
Palladium(II) oxide black-green or amber solid 122.4 87 750
(dec.)
insoluble soluble in dilute aqua regia, 48% hydrobromic acid
Palladium(II) acetate trimer gold brown crystals 673.53 47.4   insoluble soluble in acetic acid
Palladium(II) nitrate brown salt 229.94 (anhydrous) ~46.2 dec. soluble soluble in dilute nitric acid
Potassium chloropalladate cubic red crystals 397.3 53.6 (dec.)    
Potassium tetrachloropalladate(II) reddish-brown crystals 326.4 32.6 524 soluble slightly soluble in hot alcohol
Sodium tetrachloropalladate(II) red brown powder 294.21 37      
Tetraammine-palladium(II) chloride yellow 245.4 43.4   soluble  
Tetraammine palladium hydrogen carbonate   219.4 48.5 181
(dec.)
soluble (56.2 g/Liter at 20 °C)  
Tetrachloropalladic(II) acid dark brown 250.2 42.5     only stable in solution of hydrochloric acid
Tetrakis(triphenyl-phosphine) palladium(0) yellow crystals 1155.58 9.2   insoluble soluble in acetone, chlorinated hydrocarbons, benzene
cis-Diamminedichloro-palladium(II) yellow crystals       soluble
(1.7 g/Liter)
soluble in ammonium hydroxide
trans-Diamminedichloro-palladium(II) orange crystals 211.39 50.3   soluble
(2.7 g/Liter)
soluble in ammonium hydroxide
trans-Dichlorobis (triphenylphosphine) palladium(II) yellow crystals 701.91 15.2      

Processes for the production of important palladium compounds

Ammine complexes of palladium: Addition of ammonia to solutions of palladium(II) chloride first causes the formation of a pink precipitate of the binuclear complex Pd(NH3)4PdCl4, Vauquelin's salt, which is converted to soluble tetraammine palladium(II) chloride by further addition of ammonia.
Acidification of this solution with HCL yields the sparingly soluble light-yellow trans-diamminedichloropalladium(II) (NH3)2PdCl2.
Ammonium hexachloropalladate(IV) is an oxidation product of ammonium tetrachloropalladate(II).

Palladium(II) acetate: This compound is prepared from palladium sponge (or nitrate) and glacial acetic acid.

Palladium(II) chloride: Palladium(II) chloride is prepared by the careful evaporation of a solution of hydrogen tetrachloropalladate(II) in hydrochloric acid, preferably in a rotary evaporator.

Palladium(II) nitrate: This compound is prepared from palladium and nitric acid.

Palladium(II) oxide: Palladium(II) oxide is obtained by reaction of palladium black (powder) with oxygen or air at 750 °C. Decomposition occurs at 850 °C. A catalytically active palladium preparation analogous to platinum(IV) oxide (PtO2[H2O]x) can be obtained by evaporating a solution of hydrogen tetrachloropalladate(II) and sodium nitrate and fusing the product.

Tetrachloropalladic(II) acid: The metal is dissolved in hydrochloric acid/chlorine or hydrochloric acid/nitric acid. If dissolution occurs below about 50 °C, hexachloropalladic(IV) acid is formed first. Commercial solutions in hydrochloric acid contain 20% palladium.


Uses of palladium metal

Electronics and electrical technology: Silver-palladium alloys are used for electrical contacts, and other palladium alloys are used for electrical relays and switching systems in telecommunication equipment. In low-current technology, electrical contacts of palladium and its alloys are used. Large numbers of so-called reed contacts (silver-palladium-, rhodium- or ruthenium-coated contacts) have been used in telephone relays. Palladium can sometimes replace gold in coatings for electronics, electrical connectors and lead frames of semiconductors (Kroschwitz, 1996). The plating solutions contain palladium(II) diamminedinitrite [Pd(NH3)2(NO2)2], the tetraammine complex or palladium(II) chloride (Smith et al., 1978; Renner, 1992; Kroschwitz, 1996).

Automobile exhaust catalysts: For more than 20 years, automobile exhaust catalysts have been used to reduce levels of nitrogen oxides, carbon monoxide and hydrocarbons in automobile exhausts. In the last few years, catalysts employing precious metal combinations of platinum or palladium and rhodium in a ratio of 5 to 1 (1.4-1.8 g PGM/Liter catalyst volume) have been developed successfully (Abthoff et al., 1994; Degussa, 1995; Kroschwitz, 1996). Exhaust gas purification by equipping of passenger car diesel engines with palladium oxidation catalysts has been achieved only since about 1989 (Fabri et al., 1990), but more recent information shows that palladium is not used on diesel vehicles, which account for around 23% of the European market (Cowley, 1997). Concentrations of the precious metals vary and depend upon the specifications of the manufacturer (IPCS, 1991). Much of this information is proprietary.
Worldwide demand for palladium in automobile catalysts rose from 23.5 tonnes in 1993 tonnes to 76.4 tonnes in 1996 (see Table 8). Around 60% of European gasoline cars sold in 1997 were equipped with palladium-based catalysts. North American car makers continued to use platinum-rich underbody catalysts, but there was increasing use of palladium starter catalysts to meet the hydrocarbon limits imposed by low-emission vehicle legislation. Many Japanese cars are equipped with palladium systems, whereas platinum-rich technology remains dominant elsewhere in Asia (Cowley, 1997).

Catalysts in chemical processes: Palladium has a strong catalytic activity for hydrogenation, dehydrogenation, oxidation and hydrogenolysis reactions. Industrial palladium catalysts are in the form of finely divided powder, wire or gauze or supported on substrates such as activated carbon, gamma-aluminium oxide or aluminium silicates. Often, two or more PGMs are combined (Table 9). In the petroleum industry, PGM catalysts are used to produce gasolines with high antiknock properties. Palladium(II) chloride and tetrachloropalladic(II) acid are important homogeneous catalysts used in the large-scale oxidation of ethylene to acetaldehyde in the Wacker process. Palladium catalysts are also used for the acetoxylation of ethylene to vinyl acetate (Fishbein, 1976) and in the manufacture of sulfuric acid and methanol (Smith et al., 1978; Kroschwitz, 1996).


Uses of important palladium compounds

Ammine complexes of palladium: The compounds and reactions are important in the industrial separation of palladium, i.e., chloropalladosamine is a precurser of metallic palladium sponge. It is also used in electroless plating and bright palladium plating. Ammonium hexachloropalladate(IV) is important in separation technology.

Palladium(II) acetate: Palladium(II) acetate is of some importance in preparative chemistry. It is used as a catalyst.

Palladium(II) chloride: Palladium(II) chloride is used in plating baths. Pellets or monoliths of oxidation catalysts are either immersed in an aqueous solution of palladium(II) chloride (impregnation technique) or sprayed with a solution of this chemical.
Other uses for palladium(II) chloride include photography, toning solutions, electroplating parts of clocks and watches, detecting carbon monoxide leaks in buried gas pipes, manufacture of indelible ink and preparation of metal for use as a catalyst (Budavari et al., 1996; Olden, 1997). Different purity grades of palladium(II) chloride ranging from 99% to 99.999% are available for chemical or medical use.

Palladium(II) nitrate: Palladium(II) nitrate is used as a catalyst in organic syntheses and in the separation of chlorine and iodine.

Palladium(II) oxide: Palladium(II) oxide is used as a hydrogenation catalyst in the synthesis of organic compounds.

Hydrogen tetrachloropalladate(II): The solution of hydrogen tetrachloropalladate(II) is an industrially important palladium preparation. It is the starting material for many other palladium compounds, particularly catalysts.

Tetraammine palladium hydrogen carbonate: Tetraammine palladium hydrogen carbonate is used as an intermediate in the production of automobile catalysts.


Examples of the catalytic activity of palladium
Principal metal Additional metal Reaction
Pt, Pd, Ir Au oxidative dehydrogenation of alkanes, n-butene to butadiene, methanol to formaldehyde, dehydrogenation of alkylcyclohexanes, isomerization and dehydrogenation of alkylcyclohexanes or alkylcyclopentanes, hydrogenative cleavage of alkanes, dealkylation of alkylaromatics
Pd (powder form) Sn, Zn, Pb selective hydrogenation of alkynes to alkanes
Pd Ni, Rh, Ag alkane dehydrogenation and dehydrocyclization