Palladium

Not to be confused with Platinum.

Palladium, 46Pd
Palladium
Pronunciation/pəˈleɪdiəm/ ⓘ ​(pə-LAY-dee-əm)
Appearancesilvery white
Standard atomic weight Ar°(Pd)
  • 106.42±0.01[1]
  • 106.42±0.01 (abridged)[2]
Palladium in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
Ni
↑
Pd
↓
Pt
rhodium ← palladium → silver
Atomic number (Z)46
Groupgroup 10
Periodperiod 5
Block  d-block
Electron configuration[Kr] 4d10
Electrons per shell2, 8, 18, 18
Physical properties
Phase at STPsolid
Melting point1828.05 K ​(1554.9 °C, ​2830.82 °F)
Boiling point3236 K ​(2963 °C, ​5365 °F)
Density (at 20° C)12.007 g/cm3[3]
when liquid (at m.p.)10.38 g/cm3
Heat of fusion16.74 kJ/mol
Heat of vaporization358 kJ/mol
Molar heat capacity25.98 J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 1721 1897 2117 2395 2753 3234
Atomic properties
Oxidation statescommon: 0, +2, +4
+1,[4] +3,[5] +5[6]
ElectronegativityPauling scale: 2.20
Ionization energies
  • 1st: 804.4 kJ/mol
  • 2nd: 1870 kJ/mol
  • 3rd: 3177 kJ/mol
Atomic radiusempirical: 137 pm
Covalent radius139±6 pm
Van der Waals radius163 pm
Spectral lines of palladium
Other properties
Natural occurrenceprimordial
Crystal structure ​face-centered cubic (fcc) (cF4)
Lattice constant
a = 389.02 pm (at 20 °C)[3]
Thermal expansion11.77×10−6/K (at 20 °C)[3]
Thermal conductivity71.8 W/(m⋅K)
Electrical resistivity105.4 nΩ⋅m (at 20 °C)
Magnetic orderingparamagnetic[7]
Molar magnetic susceptibility+567.4×10−6 cm3/mol (288 K)[8]
Young's modulus121 GPa
Shear modulus44 GPa
Bulk modulus180 GPa
Speed of sound thin rod3070 m/s (at 20 °C)
Poisson ratio0.39
Mohs hardness4.75
Vickers hardness400–600 MPa
Brinell hardness320–610 MPa
CAS Number7440-05-3
History
Namingafter asteroid Pallas, itself named after Pallas Athena
Discovery and first isolationWilliam Hyde Wollaston (1802)
Isotopes of palladium
Main isotopes[9] Decay
Isotope abun­dance half-life (t1/2) mode pro­duct
100Pd synth 3.63 d ε 100Rh
102Pd 1.02% stable
103Pd synth 16.99 d ε 103Rh
104Pd 11.1% stable
105Pd 22.3% stable
106Pd 27.3% stable
107Pd trace 6.5×106 y β− 107Ag
108Pd 26.5% stable
110Pd 11.7% stable

Palladium is a chemical element; it has symbol Pd and atomic number 46. It is a rare and lustrous silvery-white metal discovered in 1802 by the English chemist William Hyde Wollaston. He named it after the asteroid Pallas (formally 2 Pallas), which was itself named after the epithet of the Greek goddess Athena, acquired by her when she slew Pallas. Palladium, platinum, rhodium, ruthenium, iridium and osmium form together a group of elements referred to as the platinum group metals. They have similar chemical properties, but palladium has the lowest melting point and is the least dense of them.

More than half the supply of palladium and its congener platinum is used in catalytic converters, which convert as much as 90% of the harmful gases in automobile exhaust (hydrocarbons, carbon monoxide, and nitrogen dioxide[10]) into nontoxic substances (nitrogen, carbon dioxide and water vapor). Palladium is also used in electronics, dentistry, medicine, hydrogen purification, chemical applications,[11][12] electrochemical sensors,[13] electrosynthesis,[14][15] groundwater treatment, and jewellery. Palladium is a key component of fuel cells, in which hydrogen and oxygen react to produce electricity, heat, and water.

Ore deposits of palladium and other platinum group metals are rare. The most extensive deposits have been found in the norite belt of the Bushveld Igneous Complex covering the Transvaal Basin in South Africa; the Stillwater Complex in Montana, United States; the Sudbury Basin and Thunder Bay District of Ontario, Canada; and the Norilsk Complex in Russia. Recycling is also a source, mostly from scrapped catalytic converters. The numerous applications and limited supply sources result in considerable investment interest.

  1. ^ "Standard Atomic Weights: Palladium". CIAAW. 1979.
  2. ^ Prohaska, Thomas; Irrgeher, Johanna; Benefield, Jacqueline; Böhlke, John K.; Chesson, Lesley A.; Coplen, Tyler B.; Ding, Tiping; Dunn, Philip J. H.; Gröning, Manfred; Holden, Norman E.; Meijer, Harro A. J. (4 May 2022). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN 1365-3075.
  3. ^ a b c Arblaster, John W. (2018). Selected Values of the Crystallographic Properties of Elements. Materials Park, Ohio: ASM International. ISBN 978-1-62708-155-9.
  4. ^ Pd(I) is known in [Pd2]2+ compounds; see Christoph Fricke; Theresa Sperger; Marvin Mendel; Franziska Schoenebeck (2020). "Catalysis with Palladium(I) Dimers". Angewandte Chemie International Edition. 60 (7): 3355–3366. doi:10.1002/anie.202011825. PMC 7898807. PMID 33058375.
  5. ^ Pd(III) has been observed; see Powers, D. C.; Ritter, T. (2011). "Palladium(III) in Synthesis and Catalysis" (PDF). Higher Oxidation State Organopalladium and Platinum Chemistry. Topics in Organometallic Chemistry. Vol. 35. pp. 129–156. Bibcode:2011hoso.book..129P. doi:10.1007/978-3-642-17429-2_6. ISBN 978-3-642-17428-5. PMC 3066514. PMID 21461129. Archived from the original (PDF) on 12 June 2013.
  6. ^ Palladium(V) has been identified in complexes with organosilicon compounds containing pentacoordinate palladium; see Shimada, Shigeru; Li, Yong-Hua; Choe, Yoong-Kee; Tanaka, Masato; Bao, Ming; Uchimaru, Tadafumi (2007). "Multinuclear palladium compounds containing palladium centers ligated by five silicon atoms". Proceedings of the National Academy of Sciences. 104 (19): 7758–7763. Bibcode:2007PNAS..104.7758S. doi:10.1073/pnas.0700450104. PMC 1876520. PMID 17470819.
  7. ^ Lide, D. R., ed. (2005). "Magnetic susceptibility of the elements and inorganic compounds". CRC Handbook of Chemistry and Physics (PDF) (86th ed.). Boca Raton (FL): CRC Press. ISBN 0-8493-0486-5.
  8. ^ Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. pp. E110. ISBN 0-8493-0464-4.
  9. ^ Kondev, F. G.; Wang, M.; Huang, W. J.; Naimi, S.; Audi, G. (2021). "The NUBASE2020 evaluation of nuclear properties" (PDF). Chinese Physics C. 45 (3) 030001. doi:10.1088/1674-1137/abddae.
  10. ^ Gao, Chuan; Wang, Houlin; Zhou, Bin; Wang, Bin; Wang, Rong; Long, Yunpeng; Wang, Dong; Peng, Yue; Li, Junhua (11 November 2024). "Palladium-assisted NOx storage and release on CexZr1-xO2 for passive NOx adsorber in diesel exhaust aftertreatment". Communications Engineering. 3 (1): 164. doi:10.1038/s44172-024-00311-3. PMC 11555237. PMID 39528686.
  11. ^ Hacıefendioğlu, Duygu; Tuncel, Ali (June 2025). "N-heterocyclic carbene-palladium complex immobilized on Co-MOF 74 microrods as a highly selective catalyst for Suzuki–Miyaura cross-coupling". Reaction Kinetics, Mechanisms and Catalysis. 138 (3): 1363–1380. doi:10.1007/s11144-024-02777-w.
  12. ^ Zhang, Yunkai; Wang, Lei; Zhou, Shenghu (June 2025). "Supported Pd–B alloy mesoporous nanospheres as efficient catalysts for nitrobenzene hydrogenation". Reaction Kinetics, Mechanisms and Catalysis. 138 (3): 1381–1391. doi:10.1007/s11144-024-02793-w.
  13. ^ Ranjithkumar, Karuppaiya; Narmatha, Sivaraman; Sekar, Ramachandran; Sathiya, Paulraj; Thangamuthu, Rangasamy; Kumar, Sakkarapalayam Murugesan Senthil (January 2025). "Fabrication of electrodeposited palladium thin-film electrodes for electrochemical sensing of acetaminophen". Journal of Materials Science: Materials in Electronics. 36 (1) 48. doi:10.1007/s10854-024-14112-z.
  14. ^ Perry, Samuel C.; Pangotra, Dhananjai; Vieira, Luciana; Csepei, Lénárd-István; Sieber, Volker; Wang, Ling; Ponce de León, Carlos; Walsh, Frank C. (19 June 2019). "Electrochemical synthesis of hydrogen peroxide from water and oxygen". Nature Reviews Chemistry. 3 (7): 442–458. doi:10.1038/s41570-019-0110-6.
  15. ^ Zhou, Ting-Ting; Dong, Kai-Yu; Zheng, Zhe; Yuan, Qiang (May 2025). "Coupling of alloying and interface effects in dendritic Au-doped PtPd alloy/dumbbell-like bismuth telluride heterostructures for ethanol and methanol electrooxidation". Rare Metals. 44 (5): 3119–3129. Bibcode:2025RareM..44.3119Z. doi:10.1007/s12598-024-03145-2.
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