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{{About|the chemical element}}
{{distinguish|Platinum}}
{{Use dmy dates|date=February 2021}}
{{Infobox palladium}}
'''Palladium''' is a [[chemical element]]; it has [[Symbol (chemistry)|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 (daughter of Triton)|Pallas]]. Palladium, [[platinum]], [[rhodium]], [[ruthenium]], [[iridium]] and [[osmium]] form together a group of elements referred to as the [[platinum group]] metals (PGMs). 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 (chemistry)|congener]] platinum is used in [[catalytic converter]]s, which convert as much as 90% of the harmful gases in automobile exhaust ([[hydrocarbon]]s, [[carbon monoxide]], and [[nitrogen dioxide]]<ref>{{cite journal |last1=Gao |first1=Chuan |last2=Wang |first2=Houlin |last3=Zhou |first3=Bin |last4=Wang |first4=Bin |last5=Wang |first5=Rong |last6=Long |first6=Yunpeng |last7=Wang |first7=Dong |last8=Peng |first8=Yue |last9=Li |first9=Junhua |title=Palladium-assisted NOx storage and release on CexZr1-xO2 for passive NOx adsorber in diesel exhaust aftertreatment |journal=Communications Engineering |date=11 November 2024 |volume=3 |issue=1 |page=164 |doi=10.1038/s44172-024-00311-3 |pmc=11555237 |pmid=39528686 }}</ref>) into nontoxic substances ([[nitrogen]], [[carbon dioxide]] and [[water vapor]]). Palladium is also used in electronics, [[dentistry]], [[medicine]], [[hydrogen purification]], chemical applications,<ref>{{cite journal |last1=Hacıefendioğlu |first1=Duygu |last2=Tuncel |first2=Ali |title=N-heterocyclic carbene-palladium complex immobilized on Co-MOF 74 microrods as a highly selective catalyst for Suzuki–Miyaura cross-coupling |journal=Reaction Kinetics, Mechanisms and Catalysis |date=June 2025 |volume=138 |issue=3 |pages=1363–1380 |doi=10.1007/s11144-024-02777-w }}</ref><ref>{{cite journal |last1=Zhang |first1=Yunkai |last2=Wang |first2=Lei |last3=Zhou |first3=Shenghu |title=Supported Pd–B alloy mesoporous nanospheres as efficient catalysts for nitrobenzene hydrogenation |journal=Reaction Kinetics, Mechanisms and Catalysis |date=June 2025 |volume=138 |issue=3 |pages=1381–1391 |doi=10.1007/s11144-024-02793-w }}</ref> electrochemical sensors,<ref>{{cite journal |last1=Ranjithkumar |first1=Karuppaiya |last2=Narmatha |first2=Sivaraman |last3=Sekar |first3=Ramachandran |last4=Sathiya |first4=Paulraj |last5=Thangamuthu |first5=Rangasamy |last6=Kumar |first6=Sakkarapalayam Murugesan Senthil |title=Fabrication of electrodeposited palladium thin-film electrodes for electrochemical sensing of acetaminophen |journal=Journal of Materials Science: Materials in Electronics |date=January 2025 |volume=36 |issue=1 |article-number=48 |doi=10.1007/s10854-024-14112-z }}</ref> electrosynthesis,<ref>{{cite journal |last1=Perry |first1=Samuel C. |last2=Pangotra |first2=Dhananjai |last3=Vieira |first3=Luciana |last4=Csepei |first4=Lénárd-István |last5=Sieber |first5=Volker |last6=Wang |first6=Ling |last7=Ponce de León |first7=Carlos |last8=Walsh |first8=Frank C. |title=Electrochemical synthesis of hydrogen peroxide from water and oxygen |journal=Nature Reviews Chemistry |date=19 June 2019 |volume=3 |issue=7 |pages=442–458 |doi=10.1038/s41570-019-0110-6 }}</ref><ref>{{cite journal |last1=Zhou |first1=Ting-Ting |last2=Dong |first2=Kai-Yu |last3=Zheng |first3=Zhe |last4=Yuan |first4=Qiang |title=Coupling of alloying and interface effects in dendritic Au-doped PtPd alloy/dumbbell-like bismuth telluride heterostructures for ethanol and methanol electrooxidation |journal=Rare Metals |date=May 2025 |volume=44 |issue=5 |pages=3119–3129 |doi=10.1007/s12598-024-03145-2 |bibcode=2025RareM..44.3119Z }}</ref> [[Groundwater remediation|groundwater treatment]], and jewellery. Palladium is a key component of [[fuel cell]]s, in which hydrogen and oxygen react to produce electricity, heat, and water.
[[Ore]] [[Deposit (geology)|deposits]] of palladium and other PGMs 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|Norilsk Complex]] in Russia. [[Recycling]] is also a source, mostly from scrapped catalytic converters. The numerous applications and limited supply sources result in considerable [[Palladium as an investment|investment]] interest.
== Characteristics ==
Palladium belongs to [[group 10 element|group 10]] in the periodic table, but the configuration in the outermost electrons is in accordance with [[Hund's rule]]. Electrons that by the [[Madelung rule]] would be expected to occupy the 5[[Atomic orbital|''s'']] instead fill the 4[[Atomic orbital|''d'' orbitals]], as it is more energetically favorable to have a completely filled 4d<sup>10</sup> shell instead of the 5s<sup>2</sup> 4d<sup>8</sup> configuration.{{clarify|date=August 2019}}
{| class="wikitable floatleft" border="1" cellpadding="3" cellspacing="0"
|-
![[Atomic number|Z]] !! [[Chemical element|Element]] !! [[Electron shell|No. of electrons/shell]]
|-
| 28 || [[nickel]] || 2, 8, 16, 2 (or 2, 8, 17, 1)
|-
| 46 || palladium || 2, 8, 18, 18, <span title="The valence shell shouldn’t be omitted!">0</span>
|-
| 78 || [[platinum]] || 2, 8, 18, 32, 17, 1
|-
| 110 || [[darmstadtium]] || 2, 8, 18, 32, 32, 16, 2 (predicted)<ref>{{cite book |title=The Chemistry of the Actinide and Transactinide Elements |editor1-last=Morss |editor2-first=Norman M. |editor2-last=Edelstein |editor3-last=Fuger |editor3-first=Jean |last1=Hoffman |first1=Darleane C. |last2=Lee |first2=Diana M. |last3=Pershina |first3=Valeria |chapter=Transactinides and the future elements |publisher=[[Springer Science+Business Media]] |year=2006 |isbn=1-4020-3555-1 |___location=Dordrecht, The Netherlands |edition=3rd |page=1722}}</ref>
|}
This 5s<sup>0</sup> configuration, unique in [[period 5 element|period 5]], makes palladium the heaviest element having only ''one'' incomplete [[electron shell]], with all shells above it empty.
Palladium has the appearance of a soft silver-white metal that resembles platinum. It is the least dense and has the lowest [[melting point]] of the platinum group metals. It is soft and [[ductile]] when [[Annealing (metallurgy)|annealed]] and is greatly increased in strength and hardness when cold-worked. Palladium dissolves slowly in concentrated [[nitric acid]], in hot, concentrated [[sulfuric acid]], and when finely ground, in [[hydrochloric acid]].<ref name="CRC">{{cite book |author=Hammond, C. R. |chapter=The Elements |title=Handbook of Chemistry and Physics |edition=81st |publisher=CRC press |isbn=978-0-8493-0485-9 |date=2004 |chapter-url-access=registration |chapter-url=https://archive.org/details/crchandbookofche81lide}}</ref> It dissolves readily at room temperature in [[aqua regia]].
Palladium does not react with [[oxygen]] at standard temperature (and thus does not tarnish in [[air]]). Palladium heated to 800 °C will produce a layer of palladium(II) oxide (PdO). It may slowly develop a slight brownish coloration over time, likely due to the formation of a surface layer of its monoxide.
Palladium films with defects produced by alpha particle bombardment at low temperature exhibit superconductivity having ''T''<sub>c</sub> = 3.2 K.<ref>B. Strizker, Phys. Rev. Lett., 42, 1769 (1979).</ref>
=== Isotopes ===
{{Main|Isotopes of palladium}}
Naturally occurring palladium is composed of six stable [[isotope]]s. The most stable [[radioisotope]]s are [[Palladium-107|<sup>107</sup>Pd]] with a [[half-life]] of 6.5 million years (traces found in nature), [[Pd-103|<sup>103</sup>Pd]] with a half-life of 16.99 days, and <sup>100</sup>Pd with a half-life of 3.63 days. There are 25 other radioisotopes characterized ranging from <sup>91</sup>Pd to <sup>129</sup>Pd. These have half-lives of less than thirty minutes, except <sup>101</sup>Pd (8.47 hours), <sup>109</sup>Pd (13.6 hours), and <sup>112</sup>Pd (21.0 hours).<ref name="NUBASE">{{NUBASE2020}}</ref>
For isotopes with atomic masses less than that of the most abundant stable isotope, <sup>106</sup>Pd, the primary [[decay mode]] is [[electron capture]] with the primary [[decay product]] being rhodium. The primary mode of decay for those isotopes of Pd with atomic mass greater than 106 is [[beta decay]] with the primary product of this decay being [[silver]].<ref name="NUBASE" />
[[Radiogenic]] <sup>107</sup>Ag is a decay product of <sup>107</sup>Pd and was first discovered in 1978<ref>{{cite journal |title=Evidence for the existence of <sup>107</sup>Pd in the early solar system |journal=Philosophical Transactions of the Royal Society of London, Series A |first3=R. |date=1978 |volume=359 |last3=Hutchison |pages=1079–1082 |doi=10.1098/rsta.2001.0893 |first1=W. R. |last1=Kelly |first2=G. J. |last2=Gounelle |issue=1787 |bibcode=2001RSPTA.359.1991R }}</ref> in the [[Santa Clara, Durango|Santa Clara]]<ref>{{cite web |url=http://mexicogemstones.com/pdf/MexicoMeteorites.pdf |archive-url=https://web.archive.org/web/20060506085632/http://www.mexicogemstones.com/pdf/MexicoMeteorites.pdf |url-status=dead |archive-date=2006-05-06 |title=Mexico's Meteorites |work=mexicogemstones.com}}</ref> meteorite of 1976. The discoverers suggest that the coalescence and differentiation of iron-cored small planets may have occurred 10 million years after a [[nucleosynthetic]] event. <sup>107</sup>Pd versus Ag correlations observed in [[Solar System]] bodies must reflect the presence of short-lived nuclides in the early Solar System.<ref>{{cite journal |title=The isotopic composition of Ag in meteorites and the presence of <sup>107</sup>Pd in protoplanets |journal=Geochimica et Cosmochimica Acta |date=1990 |volume=54 |issue=6 |pages=1729–1743 |doi=10.1016/0016-7037(90)90404-9 |first1=J. H. |last1=Chen |first2=G. J. |last2=Wasserburg |bibcode=1990GeCoA..54.1729C}}</ref>
{{chem|107|Pd}} is also produced as a [[fission product]] in spontaneous or induced fission of {{chem|235|U|link=Uranium-235}}. As it is not very mobile in the environment and has a relatively low [[decay energy]], {{chem|107|Pd}} is usually considered to be among the more benign of the [[long-lived fission products]].
== Compounds ==
{{Main|Palladium compounds}}
Palladium compounds exist primarily in the 0 and +2 oxidation state. Other less common states are also recognized. Generally the compounds of palladium are more similar to those of platinum than those of any other element.
<gallery mode="packed">
File:Alpha-palladium(II)-chloride-xtal-3D-balls.png|Structure of ''α''-PdCl<sub>2</sub>
File:Pd6Cl12-from-xtal-1996-CM-3D-ellipsoids.png|{{center|Structure of ''β''-PdCl<sub>2</sub>}}
</gallery>
=== Palladium(II) ===
[[Palladium(II) chloride]] is the principal starting material for other palladium compounds. It arises by the reaction of palladium with chlorine. It is used to prepare heterogeneous palladium catalysts such as palladium on barium sulfate, palladium on carbon, and palladium chloride on carbon.<ref>{{OrgSynth|title = Palladium Catalysts|author = Mozingo, Ralph |collvol = 3|collvolpages = 685|year = 1955|prep = cv3p0685}}</ref> Solutions of {{chem2|PdCl2}} in nitric acid react with [[acetic acid]] to give [[palladium(II) acetate]], also a versatile reagent. {{chem2|PdCl2}} reacts with [[ligands]] (L) to give square planar complexes of the type {{chem2|PdCl2L2}}. One example of such complexes is the [[benzonitrile]] derivative [[Bis(benzonitrile)palladium dichloride|{{chem2|PdCl2(PhCN)2}}]].<ref>{{cite book |pages=60–63 |volume=28 |doi=10.1002/9780470132593.ch13 |date=1990 |first1=Gordon K. |last1=Anderson |first2=Minren |last2=Lin |last3=Sen |first3=Ayusman |last4=Gretz |first4=Efi |title=Inorganic Syntheses |chapter=Bis(Benzonitrile)Dichloro Complexes of Palladium and Platinum |isbn=978-0-470-13259-3}}</ref><ref>{{cite journal |doi=10.1134/S1070328408110110 |title=Palladium complexes based on optically active terpene derivatives of ethylenediamine |journal=Russian Journal of Coordination Chemistry |volume=34 |issue=11 |pages=855–857 |year=2008 |last1=Zalevskaya |first1=O. A |last2=Vorob'eva |first2=E. G |last3=Dvornikova |first3=I. A |last4=Kuchin |first4=A. V }}</ref>
: {{chem2|PdCl2 + 2 L → PdCl2L2}} (L = [[PhCN]], [[Triphenylphosphine|PPh<sub>3</sub>]], [[Ammonia|NH<sub>3</sub>]], etc.)
The complex [[bis(triphenylphosphine)palladium(II) dichloride]] is a useful catalyst.<ref>{{OrgSynth|title = Palladium-catalyzed reaction of 1-alkenylboronates with vinylic halides: (1Z,3E)-1-Phenyl-1,3-octadiene|collvol = 8|collvolpages = 532|author1-link=Norio Miyaura|author1= Miyaura, Norio|author2 = Suzuki, Akira|name-list-style=amp|year = 1993|prep = cv8p0532}}</ref>
[[File:Pd(OAc)2.jpg|thumb|left|[[Palladium(II) acetate]]]]
[[File:Platinum-palladium ore, Stillwater mine MT.JPG|thumb|Platinum-palladium ore from the Stillwater mine in the Beartooth Mountains, Montana, US]]
[[File:Sulfidic serpentintite (platinum-palladium ore) Johns-Manville Reef, Stillwater Complex.jpg|thumb|Sulfidic serpentintite (platinum-palladium ore) from the Stillwater mine in Montana]]
=== Palladium(0) ===
Palladium forms a range of zerovalent complexes with the formula {{chem2|PdL4}}, {{chem2|PdL3}} and {{chem2|PdL2}}. For example, reduction of a mixture of {{chem2|PdCl2(PPh3)2}} and {{chem2|PPh3}} gives [[tetrakis(triphenylphosphine)palladium(0)]]:<ref>{{cite book |volume=13 |pages=121–124 |first1=D. R. |last1=Coulson |doi=10.1002/9780470132449.ch23 |date=1972 |last2=Satek |first2=L. C. |last3=Grim |first3=S. O. |chapter=Tetrakis(triphenylphosphine)palladium(0) |title=Inorganic Syntheses |isbn=978-0-470-13244-9}}</ref>
: {{chem2|2 PdCl2(PPh3)2 + 4 PPh3 + 5 [[Hydrazine|N2H4]] → 2 Pd(PPh3)4 + N2 + 4 N2H5+Cl-}}
Another major palladium(0) complex, [[tris(dibenzylideneacetone)dipalladium(0)]] ({{chem2|Pd2(dba)3}}), is prepared by reducing [[sodium tetrachloropalladate]] in the presence of [[dibenzylideneacetone]].<ref>{{cite journal |doi=10.1039/C29700001065 |title=A novel palladium(0) complex; bis(dibenzylideneacetone)palladium(0) |journal=Journal of the Chemical Society D: Chemical Communications |issue=17 |pages=1065 |year=1970 |last1=Takahashi |first1=Y |last2=Ito |first2=Ts |last3=Sakai |first3=S |last4=Ishii |first4=Y}}</ref>
Palladium(0), as well as palladium(II), are catalysts in [[palladium-catalyzed coupling reactions|coupling reactions]], as has been recognized by the 2010 [[Nobel Prize in Chemistry]] to [[Richard F. Heck]], [[Ei-ichi Negishi]], and [[Akira Suzuki]]. Such reactions are widely practiced for the synthesis of fine chemicals. Prominent coupling reactions include the [[Heck reaction|Heck]], [[Suzuki reaction|Suzuki]], [[Sonogashira coupling]], [[Stille reaction]]s, and the [[Kumada coupling]]. [[Palladium(II) acetate]], [[tetrakis(triphenylphosphine)palladium(0)]] ({{chem2|Pd(PPh3)4}}), and [[tris(dibenzylideneacetone)dipalladium(0)]] ({{chem2|Pd2(dba)3}}) serve either as catalysts or precatalysts.<ref>{{cite book |chapter-url=https://books.google.com/books?id=WLb962AKlSEC&pg=PA392 |chapter=Application to Organic Synthesis |page=392 |title=The Organometallic Chemistry of the Transition Metals |first=Robert H. |last=Crabtree |publisher=John Wiley and Sons |date=2009 |isbn=978-0-470-25762-3}}</ref>
=== Other oxidation states ===
Although Pd(IV) compounds are comparatively rare, one example is [[sodium hexachloropalladate(IV)]], {{chem2|Na2[PdCl6]}}. A few [[compounds of palladium(III)]] are also known.<ref>{{Cite book |doi=10.1007/978-3-642-17429-2_6 |pmid=21461129 |pmc=3066514 |chapter=Palladium(III) in Synthesis and Catalysis |title=Higher Oxidation State Organopalladium and Platinum Chemistry |volume=35 |pages=129–156 |series=Topics in Organometallic Chemistry |year=2011 |last1=Powers |first1=David C |last2=Ritter |first2=Tobias |isbn=978-3-642-17428-5}}</ref> Palladium(VI) was claimed in 2002,<ref name="pmid11786638">{{cite journal |doi=10.1126/science.1067027 |pmid=11786638 |title=Synthesis and Structure of Formally Hexavalent Palladium Complexes |journal=Science |volume=295 |issue=5553 |pages=308–310 |year=2002 |last1=Chen |first1=W |last2=Shimada |first2=S |last3=Tanaka |first3=M |bibcode=2002Sci...295..308C }}</ref><ref name="pmid11786632">{{cite journal |doi=10.1126/science.1067921 |pmid=11786632 |title=CHEMISTRY: A New Oxidation State for Pd? |journal=Science |volume=295 |issue=5553 |pages=288–289 |year=2002 |last1=Crabtree |first1=R. H }}</ref> but subsequently disproven.<ref>{{cite journal |pmid=19750645 |year=2002 |last1=Aullón |first1=G |title=Hexakis(silyl)palladium(VI) or palladium(II with eta2-disilane ligands? |journal=Angewandte Chemie International Edition in English |volume=41 |issue=11 |pages=1956–9 |last2=Lledós |first2=A |last3=Alvarez |first3=S |doi=10.1002/1521-3773(20020603)41:11<1956::AID-ANIE1956>3.0.CO;2-#}}</ref><ref>{{cite journal |pmid=19750644 |year=2002 |last1=Sherer |first1=E. C |title=Electronic structure and bonding in hexacoordinate silyl-palladium complexes |journal=Angewandte Chemie International Edition in English |volume=41 |issue=11 |pages=1953–6 |last2=Kinsinger |first2=C. R |last3=Kormos |first3=B. L |last4=Thompson |first4=J. D |last5=Cramer |first5=C. J |doi=10.1002/1521-3773(20020603)41:11<1953::AID-ANIE1953>3.0.CO;2-H |doi-access=}}</ref>
Mixed valence palladium complexes exist, e.g. {{chem2|Pd4(CO)4(OAc)4Pd(acac)2}} forms an infinite Pd chain structure, with alternatively interconnected {{chem2|Pd4(CO)4(OAc)4}} and [[Palladium(II) bis(acetylacetonate)|Pd(acac)<sub>2</sub>]] units.<ref name="pmid25319757">{{cite journal |doi=10.1002/anie.201408461 |pmid=25319757 |title=A Motif for Infinite Metal Atom Wires |journal=Angewandte Chemie International Edition |volume=53 |issue=51 |pages=14087–14091 |year=2014 |last1=Yin |first1=Xi |last2=Warren |first2=Steven A |last3=Pan |first3=Yung-Tin |last4=Tsao |first4=Kai-Chieh |last5=Gray |first5=Danielle L |last6=Bertke |first6=Jeffery |last7=Yang |first7=Hong |bibcode=2014ACIE...5314087Y }}</ref>
When alloyed with a more [[Electronegativity|electropositive]] element, palladium can acquire a negative charge. Such compounds are known as palladides, such as [[gallium palladide]].<ref>{{cite journal |last1=Armbrüster |first1=Marc |title=Intermetallic compounds in catalysis – a versatile class of materials meets interesting challenges |journal=Science and Technology of Advanced Materials |date=31 January 2020 |volume=21 |issue=1 |pages=303–322 |doi=10.1080/14686996.2020.1758544 |pmid=33628119 |pmc=7889166 |bibcode=2020STAdM..21..303A }}</ref> Palladides with the [[stoichiometry]] {{chem2|RPd3}} exist where R is [[scandium]], [[yttrium]], or any of the [[lanthanides]].<ref>{{cite journal |last1=Wang |first1=Qiaoming |last2=Collins |first2=Gary S. |title=Nuclear quadrupole interactions of 111In/Cd solute atoms in a series of rare-earth palladium alloys |journal=Hyperfine Interactions |volume=221 |issue=1–3 |year=2013 |doi=10.1007/s10751-012-0686-4 |pages=85–98 |arxiv=1209.3822 |bibcode=2013HyInt.221...85W }}</ref>
== Occurrence ==
[[File:2005palladium (mined).PNG|thumb|upright=1.6|Palladium output in 2005]]
As overall mine production of palladium reached 210,000 kilograms in 2022, [[Russia]] was the top producer with 88,000 kilograms, followed by South Africa, Canada, the U.S., and Zimbabwe.<ref>{{Cite report |author=U. S. Geological Survey |date=2023 |title=Mineral commodity summaries 2023 |page=210 |url=https://pubs.er.usgs.gov/publication/mcs2023 |language=en |doi=10.3133/mcs2023 |doi-access=free}}</ref> Russia's company [[Norilsk Nickel]] ranks first among the largest palladium producers globally, accounting for 39% of the world's production.<ref>{{Cite web |url=https://www.nornickel.com/news-and-media/press-releases-and-news/norilsk-nickel-group-announces-preliminary-consolidated-production-results-for-4-th-quarter-and-full-2016-and-production-outlook-for-2017/?sphrase_id=316142 |title="Norilsk Nickel" Group announces preliminary consolidated production results for 4 th quarter and full 2016, and production outl |website=Nornickel |language=en-US |access-date=2018-01-29 |archive-url=https://web.archive.org/web/20180629183059/https://www.nornickel.com/news-and-media/press-releases-and-news/norilsk-nickel-group-announces-preliminary-consolidated-production-results-for-4-th-quarter-and-full-2016-and-production-outlook-for-2017/?sphrase_id=316142 |archive-date=29 June 2018 |url-status=dead}}</ref> <!--In 2005, Russia was the top producer of palladium, with at least 50% world share, followed by South Africa, Canada and the U.S., reports the [[British Geological Survey]].<ref name="BGS">{{cite book |first1=L. E. |last1=Hetherington |first2=T. J. |last2=Brown |first3=A. J. |last3=Benham |first4=T. |last4=Bide |first5=P. A. J. |last5=Lusty |first6=V. L. |last6=Hards |first7=S. D. |last7=Hannis |first8=N. E. |last8=Idoine |title=World mineral statistics British Geological Survey |url=http://www.bgs.ac.uk/downloads/start.cfm?id=1388 |place=Keyworth, Nottingham |page=88}}</ref>-->
Palladium can be found as a free metal alloyed with gold and other [[platinum-group]] metals in [[placer mining|placer]] deposits of the [[Ural Mountains]], [[Australia]], [[Ethiopia]], [[North America|North]] and [[South America]]. For the production of palladium, these deposits play only a minor role. The most important commercial sources are [[nickel]]-[[copper]] deposits found in the [[Sudbury Basin]], [[Ontario]], and the [[Norilsk|Norilsk–Talnakh]] deposits in [[Siberia]]. The other large deposit is the [[Merensky Reef]] platinum group metals deposit within the [[Bushveld Igneous Complex]] [[South Africa]]. The [[Stillwater igneous complex]] of [[Montana]] and the Roby zone ore body of the [[Lac des Îles igneous complex]] of Ontario are the two other sources of palladium in Canada and the United States.<ref name="USGS07CS" /><ref name="USGS07YB">{{cite web |url=http://minerals.usgs.gov/minerals/pubs/commodity/platinum/myb1-2007-plati.pdf |title=Platinum-Group Metals |date=January 2007 |work=Mineral Yearbook 2007 |publisher=[[United States Geological Survey]] |access-date=2 May 2010 |archive-date=9 July 2017 |archive-url=https://web.archive.org/web/20170709115319/https://minerals.usgs.gov/minerals/pubs/commodity/platinum/myb1-2007-plati.pdf |url-status=dead }}</ref> Palladium is found in the rare minerals [[cooperite (mineral)|cooperite]]<ref>{{cite journal |journal=Mineralogical Magazine |date=1994 |volume=58 |issue=2 |pages=223–234 |title=Compositional variation of cooperite, braggite, and vysotskite from the Bushveld Complex |first1=Sabine M. C. |last1=Verryn |first2=Roland K. W. |last2=Merkle |doi=10.1180/minmag.1994.058.391.05 |bibcode=1994MinM...58..223V }}</ref> and [[polarite]].<ref>{{cite journal |last1=Genkin |first1=A. D. |last2=Evstigneeva |first2=T. L. |date=1986 |title=Associations of platinum- group minerals of the Norilsk copper-nickel sulfide ores |journal=Economic Geology |volume=81 |pages=1203–1212 |doi=10.2113/gsecongeo.81.5.1203 |issue=5 |bibcode=1986EcGeo..81.1203G}}</ref> Many more Pd minerals are known, but all of them are very rare.<ref>{{Cite web |url=https://www.mindat.org/ |title=Mindat.org - Mines, Minerals and More |website=www.mindat.org}}</ref>
Palladium is also produced in [[nuclear fission]] reactors and can be extracted from [[spent nuclear fuel]] (see [[synthesis of precious metals]]), though this source for palladium is not used. None of the existing [[nuclear reprocessing]] facilities are equipped to extract palladium from the [[high-level radioactive waste]].<ref>{{cite journal |title=Recovery of Value Fission Platinoids from Spent Nuclear Fuel. Part I PART I: General Considerations and Basic Chemistry |url=http://www.platinummetalsreview.com/pdf/pmr-v47-i2-074-087.pdf |first1=Zdenek |last1=Kolarik |first2=Edouard V. |last2=Renard |journal=Platinum Metals Review |volume=47 |issue=2 |date=2003 |pages=74–87 |doi=10.1595/003214003X4727487}}</ref> A complication for the recovery of palladium in spent fuel is the presence of {{chem|107|Pd}}, a slightly radioactive [[long-lived fission product]]. Depending on end use, the radioactivity contributed by the {{chem|107|Pd}} might make the recovered palladium unusable without a costly step of [[isotope separation]].
== Applications ==
[[File:Aufgeschnittener Metall Katalysator für ein Auto.jpg|thumb|[[Multiview orthographic projection|Cross-section]] of a [[Catalytic converter|metal-core catalytic converter]]]]
[[File:RR3415-0002 25 rubles palladium 1989 Ivan III.jpg|thumb|The Soviet 25-rouble commemorative [[palladium coin]] is a rare example of the monetary usage of palladium.]]
The largest use of palladium today is in catalytic converters.<ref name="unctad" /> Palladium is also used in jewellery, [[dentistry]],<ref name="unctad" /><ref>{{cite journal |journal=Platinum Metals Review |title=Palladium in Restorative Dentistry: Superior Physical Properties make Palladium an Ideal Dental Metal |first=Roy |last=Rushforth |volume=48 |issue=1 |date=2004 |doi=10.1595/003214004X4813031 |doi-access=free}}</ref> [[watch]] making, blood sugar test strips, aircraft [[spark plug]]s, [[surgical instrument]]s, and [[electrical contact]]s.<ref>{{cite book |title=Jewelrymaking through history: an encyclopedia |first=Rayner W. |last=Hesse |publisher=Greenwood Publishing Group |date=2007 |page=146 |chapter-url=https://books.google.com/books?id=DIWEi5Hg93gC&pg=PA146 |chapter=palladium |isbn=978-0-313-33507-5}}</ref> Palladium is also used to make some professional [[transverse flute|transverse (concert or classical) flutes]].<ref>{{cite book |title=The flute book: a complete guide for students and performers |first=Nancy |last=Toff |publisher=Oxford University Press |date=1996 |page=20 |isbn=978-0-19-510502-5 |url=https://books.google.com/books?id=pCSanDD4CtsC&pg=PA20}}</ref> As a commodity, palladium [[bullion]] has [[ISO currency code]]s of XPD and 964. Palladium is one of only four metals to have such codes, the others being [[gold]], [[silver]] and platinum.<ref>{{cite book |chapter-url=https://books.google.com/books?id=2neeMTPKtEMC&pg=PA34 |chapter=Precious Metals |page=34 |title=Foreign exchange: a practical guide to the FX markets |isbn=978-0-471-73203-7 |author=Weithers, Timothy Martin |date=2006 |publisher=Wiley}}</ref> Because it [[adsorbs]] hydrogen, palladium was a key component of the controversial [[cold fusion]] experiments of the late 1980s.<ref>{{cite journal |last=Fleischmann |first=M |author2=Pons S |author3=Hawkins M |author-link=Martin Fleischmann |title=Electrochemically induced nuclear fusion of deuterium |journal=[[J. Electroanal. Chem.]] |year=1989 |volume=261 |pages=301 |doi=10.1016/0022-0728(89)80006-3 |issue=2}}</ref>
=== Catalysis ===
{{See also|Palladium-catalyzed coupling reactions}}
When it is finely divided, as with [[palladium on carbon]], palladium forms a versatile [[catalyst]]; it speeds [[Heterogeneous catalysis|heterogeneous]] catalytic processes like [[hydrogenation]], [[dehydrogenation]], and [[petroleum cracking]]. Palladium is also essential to the [[Lindlar catalyst]], also called Lindlar's Palladium.<ref>{{cite book |chapter-url=https://books.google.com/books?id=mTHQB7MkUFsC&pg=PA270 |title=Organic chemistry |author1=Brown, William Henry |author2=Foote, Christopher S |author2-link=Christopher Spencer Foote |author3=Iverson, Brent L |date=2009 |publisher=[[Cengage Learning]] |isbn=978-0-495-38857-9 |page=270 |chapter=Catalytic reduction}}</ref> A large number of [[carbon–carbon bond]]ing reactions in [[organic chemistry]] are facilitated by palladium compound catalysts. For example:
* [[Heck reaction]]
* [[Suzuki coupling]]
* [[Tsuji–Trost reaction|Tsuji-Trost reactions]]
* [[Wacker process]]
* [[Negishi reaction]]
* [[Stille coupling]]
* [[Sonogashira coupling]]
When dispersed on conductive materials, palladium is an excellent electrocatalyst for oxidation of primary alcohols in alkaline media.<ref>{{cite book |page=90 |url=https://books.google.com/books?id=RDT0OUdlj0MC&pg=PA90 |title=Palladium reagents and catalysts: new perspectives for the 21st century |first=Jiro |last=Tsuji |publisher=John Wiley and Sons |date=2004 |isbn=978-0-470-85032-9}}</ref> Palladium is also a versatile metal for [[homogeneous catalysis]], used in combination with a broad variety of [[ligand]]s for highly selective chemical transformations.
In 2010 the [[Nobel Prize in Chemistry]] was awarded "for palladium-catalyzed cross couplings in organic synthesis" to [[Richard F. Heck]], [[Ei-ichi Negishi]] and [[Akira Suzuki]]. A 2008 study showed that palladium is an effective catalyst for [[carbon–fluorine bonds]].<ref>{{cite journal |journal=[[Chemical & Engineering News]] |volume=86 |issue=35 |date=2008 |title=Palladium's Hidden Talent |pages=53–56 |first=Carmen |last=Drahl |doi=10.1021/cen-v086n035.p053}}</ref>
[[File:Kumada Catalytic Cycle.png|thumb|upright=1.8|Catalytic cycle for Kumada cross coupling reaction, which is widely used in the synthesis of fine chemicals]]
Palladium catalysis is primarily employed in organic chemistry and industrial applications, although its use is growing as a tool for [[synthetic biology]]; in 2017, effective ''in vivo'' catalytic activity of palladium [[nanoparticles]] was demonstrated in mammals to treat disease.<ref name="pmid28699627">{{cite journal |doi=10.1038/ncomms15906 |pmid=28699627 |pmc=5510178 |title=Nano-palladium is a cellular catalyst for in vivo chemistry |journal=[[Nature Communications]] |volume=8 |article-number=15906 |year=2017 |last1=Miller |first1=Miles A |last2=Askevold |first2=Bjorn |last3=Mikula |first3=Hannes |last4=Kohler |first4=Rainer H |last5=Pirovich |first5=David |last6=Weissleder |first6=Ralph |bibcode=2017NatCo...815906M}}</ref>
Palladium is also used as a catalyst in the production of [[biofuels]].<ref>{{Cite web |date=2017-08-29 |title=Biofuel production boost from catalyst made from palladium and bacteria |url=https://www.theengineer.co.uk/content/news/biofuel-production-boost-from-catalyst-made-from-palladium-and-bacteria/ |access-date=2025-05-01 |website=The Engineer |language=en}}</ref>
=== Electronics ===
The primary application of palladium in electronics is in [[multi-layer ceramic capacitor]]s<ref>{{cite web |url=http://www.ttiinc.com/object/ME_Zogbi_20030203.html |title=Shifting Supply and Demand for Palladium in MLCCs |first=Dennis |last=Zogbi |date=3 February 2003 |publisher=TTI, Inc.}}</ref> in which palladium (and palladium-silver alloy) is used for electrodes.<ref name="unctad" /> Palladium (sometimes alloyed with nickel) is or can be used for component and connector plating in consumer electronics<ref>{{cite book |author=Mroczkowski, Robert S. |title=Electronic connector handbook: theory and applications |url=https://books.google.com/books?id=XGkw8YR-uXsC&pg=SA3-PA30 |date=1998 |publisher=McGraw-Hill Professional |isbn=978-0-07-041401-3 |pages=3–}}</ref><ref>{{cite book |author=Harper, Charles A. |title=Passive electronic component handbook |url=https://books.google.com/books?id=OtlKBAcFBQAC&pg=PA580 |date=1997 |publisher=McGraw-Hill Professional |isbn=978-0-07-026698-8 |pages=580–}}</ref> and in soldering materials. The electronic sector consumed {{convert|1.07|e6ozt|t|abbr=off|order=flip}} of palladium in 2006, according to a [[Johnson Matthey]] report.<ref name="matthey">{{cite web |date=2007 |publisher=[[Johnson Matthey]] |title=Platinum 2007 |url=http://www.platinum.matthey.com/uploaded_files/2007/07_palladium.pdf |first=David |last=Jollie |archive-url=https://web.archive.org/web/20080216100834/http://www.platinum.matthey.com/uploaded_files/2007/07_palladium.pdf |archive-date=2008-02-16}}</ref> Palladium is used in the production of [[printed circuit boards]].<ref>{{Cite journal |last1=Bourgeois |first1=Damien |last2=Lacanau |first2=Valentin |last3=Mastretta |first3=Régis |last4=Contino-Pépin |first4=Christiane |last5=Meyer |first5=Daniel |date=2020 |title=A simple process for the recovery of palladium from wastes of printed circuit boards |url=https://hal.umontpellier.fr/hal-03365417v1 |journal=Hydrometallurgy |language=en |volume=191 |article-number=105241 |doi=10.1016/j.hydromet.2019.105241|bibcode=2020HydMe.19105241B }}</ref>
=== Technology ===
Hydrogen easily diffuses through heated palladium,<ref name="CRC" /> and [[membrane reactor]]s with Pd membranes are used in the production of high purity hydrogen.<ref>{{cite journal |last1=Shu |first1=J. |last2=Grandjean |first2=B. P. A. |last3=Neste |first3=A. Van |last4=Kaliaguine |first4=S. |title=Catalytic palladium-based membrane reactors: A review |journal=The Canadian Journal of Chemical Engineering |volume=69 |pages=1036 |date=1991 |doi=10.1002/cjce.5450690503 |issue=5 |bibcode=1991CJChE..69.1036S }}</ref> Palladium is used in [[palladium-hydrogen electrode]]s in electrochemical studies. [[Palladium(II) chloride]] readily catalyzes carbon monoxide gas to carbon dioxide and is useful in [[carbon monoxide detector]]s.<ref>{{cite journal |last1=Allen |first1=T. H. |last2=Root |first2=W. S. |title=An improved palladium chloride method for the determination of carbon monoxide in blood |journal=The Journal of Biological Chemistry |volume=216 |issue=1 |pages=319–323 |date=1955 |doi=10.1016/S0021-9258(19)52308-0 |pmid=13252031 |doi-access=free}}</ref>
Palladium has been used to produce [[metallic glass]] by fast cooling alloys, avoiding their crystallisation, thus reducing brittleness and leading to stronger materials.<ref>{{Cite press release |title=Glass that's Stronger than Steel |url=https://www.technologyreview.com/2011/01/11/197657/glass-thats-stronger-than-steel |language=en |access-date=2025-05-05 |website=[[MIT Technology Review]]}}</ref>
=== Hydrogen storage ===
{{Main|Palladium hydride}}
Palladium readily [[adsorbs]] hydrogen at room temperatures, forming [[palladium hydride]] PdH<sub>x</sub> with x less than 1.<ref>{{cite journal |doi=10.1007/BF02667685 |title=The H-Pd (hydrogen-palladium) System |date=1994 |last1=Manchester |first1=F. D. |last2=San-Martin |first2=A. |last3=Pitre |first3=J. M. |journal=Journal of Phase Equilibria |volume=15 |pages=62–83 }}</ref> While this property is common to many transition metals, palladium has a uniquely high absorption capacity and does not lose its ductility until x approaches 1.<ref name="gr">{{Greenwood&Earnshaw|pages=1150–151}}</ref> This property has been investigated in designing an efficient and safe hydrogen fuel storage medium, though palladium itself is currently prohibitively expensive for this purpose.<ref name="grochala">{{cite journal |last1=Grochala |first1=Wojciech |last2=Edwards |first2=Peter P. |title=Thermal Decomposition of the Non-Interstitial Hydrides for the Storage and Production of Hydrogen |journal=Chemical Reviews |volume=104 |issue=3 |pages=1283–316 |year=2004 |pmid=15008624 |doi=10.1021/cr030691s}}</ref> The content of hydrogen in palladium can be linked to [[magnetic susceptibility]], which decreases with the increase of hydrogen and becomes zero for PdH<sub>0.62</sub>. At any higher ratio, the [[solid solution]] becomes [[diamagnetic]].<ref>Mott, N. F. and Jones, H. (1958) ''The Theory of Properties of metals and alloys''. Oxford University Press. {{ISBN|0-486-60456-X}}. p. 200</ref>
Palladium is used for purification of hydrogen on a laboratory<ref>{{cite book |doi=10.1533/9780857097330.1.183 |chapter=Alternatives to palladium in membranes for hydrogen separation: Nickel, niobium and vanadium alloys, ceramic supports for metal alloys and porous glass membranes |title=Handbook of Membrane Reactors |date=2013 |last1=Santucci |first1=A. |last2=Tosti |first2=S. |last3=Basile |first3=A. |pages=183–217 |isbn=978-0-85709-414-8 }}</ref> but not industrial scale.<ref>{{cite book |doi=10.1002/14356007.o13_o04 |chapter=Hydrogen, 3. Purification |title=Ullmann's Encyclopedia of Industrial Chemistry |date=2011 |last1=Häussinger |first1=Peter |last2=Lohmüller |first2=Reiner |last3=Watson |first3=Allan M. |isbn=978-3-527-30385-4}}</ref>
=== Medicine ===
Palladium is used in small amounts (about 0.5%) in some alloys of [[dental amalgam]] to decrease corrosion and increase the [[Lustre (mineralogy)#Metallic lustre|metallic lustre]] of the final restoration.<ref>{{cite journal |last1=Colon |first1=Pierre |last2=Pradelle-Plasse |first2=Nelly |last3=Galland |first3=Jacques |title=Evaluation of the long-term corrosion behavior of dental amalgams: influence of palladium addition and particle morphology |journal=Dental Materials |volume=19 |issue=3 |pages=232–9 |year=2003 |pmid=12628436 |doi=10.1016/S0109-5641(02)00035-0}}</ref><ref>{{cite book |doi=10.1016/B978-0-323-47821-2.00010-X |chapter=Restorative Materials |title=Craig's Restorative Dental Materials |date=2019 |pages=171–208 |isbn=978-0-323-47821-2 }}</ref> Palladium is also used in the production of [[pacemakers]].<ref>{{Cite patent |number=US4514589A |title=Electrode connecting cable for cardiac pacemaker |gdate=1985-04-30 |invent1=Aldinger |invent2=Bischoff |invent3=Keilberth |invent4=Sperner |inventor1-first=Fritz |inventor2-first=Albrecht |inventor3-first=Richard |inventor4-first=Franz |url=https://patents.google.com/patent/US4514589A/en}}</ref>
=== Jewellery ===
Palladium has been used as a [[precious metal]] in jewellery since 1939 as an alternative to platinum in the alloys called "[[white gold]]", where the naturally white color of palladium does not require [[Plating#Rhodium plating|rhodium plating]]. Palladium, being much less dense than platinum, is similar to gold in that it can be beaten into [[Metal leaf|leaf]] as thin as 100 nm ({{frac|1|250,000}} in).<ref name="CRC" /> Unlike platinum, palladium may discolor at temperatures above {{convert|400|C|F}}<ref>{{cite book |first1=Dinesh C. |last1=Gupta |first2=Paul H. |last2=Langer |author3=((ASTM Committee F-1 on Electronics)) |title=Emerging semiconductor technology: a symposium |url=https://books.google.com/books?id=u-a9LvarW-8C&pg=PA273 |date=1987 |publisher=ASTM International |isbn=978-0-8031-0459-4 |pages=273–}}</ref> due to oxidation, making it more brittle and thus less suitable for use in jewellery; to prevent this, palladium intended for jewellery is heated under controlled conditions.<ref>{{Cite web |last=Mann |first=Mark B. |date=2007 |title=950 Palladium: Manufacturing Methods |work=Ganoksin |url=https://www.ganoksin.com/article/950-palladium-manufacturing-methods/}}</ref>
Prior to 2004, the principal use of palladium in jewellery was the manufacture of white gold. Palladium is one of the three most popular alloying metals in white gold ([[nickel]] and silver can also be used).<ref name="unctad">{{cite web |publisher=[[United Nations Conference on Trade and Development]] |url=http://www.unctad.org/infocomm/anglais/palladium/uses.htm |title=Palladium |access-date=5 February 2007 |archive-url=https://web.archive.org/web/20061206003556/http://www.unctad.org/infocomm/anglais/palladium/uses.htm <!--Added by H3llBot--> |archive-date=6 December 2006}}</ref> Palladium-gold is more expensive than nickel-gold, but seldom causes allergic reactions (though certain cross-allergies with nickel may occur).<ref>{{cite journal |last1=Hindsen |first1=M. |last2=Spiren |first2=A. |last3=Bruze |first3=M. |title=Cross-reactivity between nickel and palladium demonstrated by systemic administration of nickel |journal=Contact Dermatitis |volume=53 |issue=1 |pages=2–8 |year=2005 |pmid=15982224 |doi=10.1111/j.0105-1873.2005.00577.x }}</ref>
When platinum became a strategic resource during World War II, many jewellery bands were made out of palladium. Palladium was little used in jewellery because of the technical difficulty of [[Casting (metalworking)|casting]]. With the casting problem resolved<ref>{{cite web |last1=Battaini |first1=Paolo |title=The Working Properties for Jewelry Fabrication Using New Hard 950 Palladium Alloys |url=http://www.santafesymposium.org/2006-santa-fe-symposium-papers/2006-the-working-properties-for-jewellery-fabrication-using-new-hard-950-palladium-alloys |website=SANTA FE SYMPOSIUM PAPERS |date=2006}}</ref> the use of palladium in jewellery increased, originally because platinum increased in price whilst the price of palladium decreased.<ref name="wsj">{{cite news |last=Holmes |first=E. |title=Palladium, Platinum's Cheaper Sister, Makes a Bid for Love |publisher=[[The Wall Street Journal]] (Eastern edition) |date=13 February 2007 |pages=B.1}}</ref> In early 2004, when gold and platinum prices rose steeply, China began fabricating volumes of palladium jewellery, consuming 37 [[tonne]]s in 2005. Subsequent changes in the relative price of platinum lowered demand for palladium to 17.4 tonnes in 2009.<ref name="USGS09YB">{{cite web |publisher=[[United States Geological Survey]] |date=January 2007 |title=Platinum-Group Metals |work=Mineral Yearbook 2009 |url=http://minerals.usgs.gov/minerals/pubs/commodity/platinum/myb1-2009-plati.pdf |access-date=20 May 2011 |archive-date=10 January 2019 |archive-url=https://web.archive.org/web/20190110110820/https://minerals.usgs.gov/minerals/pubs/commodity/platinum/myb1-2009-plati.pdf |url-status=dead }}</ref><ref name="USGS06YB">{{cite web |publisher=[[United States Geological Survey]] |date=January 2007 |title=Platinum-Group Metals |work=Mineral Yearbook 2006 |url=http://minerals.usgs.gov/minerals/pubs/commodity/platinum/myb1-2006-plati.pdf |access-date=20 May 2011 |archive-date=11 January 2019 |archive-url=https://web.archive.org/web/20190111062032/https://minerals.usgs.gov/minerals/pubs/commodity/platinum/myb1-2006-plati.pdf |url-status=dead }}</ref> Demand for palladium as a catalyst has increased the price of palladium to about 50% higher than that of platinum in January 2019.<ref name="JMM">{{cite web |date=2019 |title=Johnson Matthey Base Prices |url=http://www.platinum.matthey.com/prices/price-tables |access-date=7 January 2019}}</ref>
In January 2010, [[hallmark]]s for palladium were introduced by assay offices in the United Kingdom, and hallmarking became mandatory for all jewellery advertising pure or alloyed palladium. Articles can be marked as 500, 950, or 999 parts of palladium per thousand of the alloy.
<!-- Johnson Matthey estimated that in 2004, with the introduction of palladium jewellery in China, demand for palladium for jewellery fabrication was {{convert|920,000|ozt|MT}}, or approximately 14% of the total palladium demand for 2004 — an increase of almost {{convert|700,000|ozt|MT}} from the previous year. This growth continued during 2005, with estimated worldwide jewellery demand for palladium of about {{convert|1,400,000|ozt|MT}} 1.4 million ounces (44 t), or almost 21% of net palladium supply, again with most of the demand centered in China. 37,000 kg in 2005 15,500 (2007) 20,200 (2008) 17,400 (2009) -->
=== Photography ===
In the [[platinotype]] printing process, photographers make fine-art black-and-white prints using platinum or palladium salts. Often used with platinum, palladium provides an alternative to silver.<ref>{{cite journal |first=Mike |last=Ware |title=Book Review of : Photography in Platinum and Palladium |journal=Platinum Metals Review |volume=49 |issue=4 |pages=190–195 |date=2005 |doi=10.1595/147106705X70291 |doi-access=free}}</ref> But palladium is more inert than the silver used in [[silver bromide]] prints, so such photographs are better archived than conventional prints and convey details more clearly.<ref>{{Cite web |last=McCabe |first=Constance |title=Noble Metals for the Early Modern Era: Platinum, Silver- Platinum, and Palladium Prints |url=https://www.moma.org/interactives/objectphoto/assets/essays/McCabe.pdf |website=[[MoMA]]}}</ref><ref>{{Cite web |last=Ware |first=Mike |title=The Technical History and Chemistry of Platinum and Palladium Printing |url=https://www.culturalheritage.org/docs/default-source/publications/books/platinum-and-palladium-photographs/46-83_ware_technicalhistorychemistry.pdf |website=Culturalheritage.org}}</ref>
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This is very minimal application and is not widely adopted
=== Art ===
Palladium leaf is one of several alternatives to [[silver]] leaf used in [[manuscript illumination]]. The use of silver leaf is problematic because it tarnishes quickly, dulling the appearance and requiring constant cleaning. Palladium is a suitable substitute owing to its resistance to tarnishing. [[Aluminium]] leaf is another inexpensive alternative, but aluminium is much more difficult to work than gold or silver and results in less-than-optimal results when employing traditional metal leafing techniques, so palladium leaf is considered the best substitute despite its considerable cost. Platinum leaf may be used to the same effect as silver leaf with similar working properties, but it is not as commercially available on demand in leaf form.<ref>{{cite book |first=Margaret |last=Morgan |title=The Bible of Illuminated Letters |publisher=Barron's Educational Series |isbn=978-0-7641-5820-9 |page=50 |year=2007}}</ref><ref>{{cite web |publisher=[[Theodore Gray]] |title=Palladium Leaf |url=http://www.theodoregray.com/PeriodicTable/Samples/046.6/index.s12.html}}</ref>
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== Research ==
=== Cold fusion ===
{{Main|Cold fusion}}
Palladium plays an important role in the ongoing research into cold-fusion energy.
=== Super tough metallic glass ===
Research is being done to develop metallic glass as a microalloy featuring palladium, a metal with a high "bulk-to-shear" stiffness ratio that counteracts the intrinsic brittleness of glassy materials. The initial samples of the new metallic glass were microalloys of palladium with [[phosphorous]], [[silicon]] and [[germanium]] that yielded glass rods approximately one millimeter in diameter. Adding [[silver]] to the mix enabled the Cal Tech researchers to expand the thickness of the glass rods to six millimeters.<ref>{{cite news |url=http://www.scientificcomputing.com/news/2011/01/new-glass-stronger-any-known-material |title=New Glass Stronger than Any Known Material |date=2011-01-11}}</ref>
=== Alternatives ===
[[Pseudo palladium]] (RhAg) is a binary alloy consisting of equal parts of rhodium (atomic number 45) and silver (atomic number 47). This alloy exhibits properties of palladium (atomic number 46).<ref>{{cite journal |last1=Kusada |first1=Kohei |last2=Yamauchi |first2=Miho |last3=Kobayashi |first3=Hirokazu |last4=Kitagawa |first4=Hiroshi |last5=Kubota |first5=Yoshiki |title=Hydrogen-Storage Properties of Solid-Solution Alloys of Immiscible Neighboring Elements with Pd |journal=Journal of the American Chemical Society |volume=132 |issue=45 |pages=15896–8 |year=2010 |pmid=20979361 |doi=10.1021/ja107362z}}</ref>
-->
== Effects on health ==
=== Toxicity ===
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| HPhrases = {{H-phrases|H317|}}
| PPhrases = {{P-phrases|P261|P273|P280|P302+352|P321|P333+313|P363|P501}}<ref>{{Sigma-Aldrich|id=373192|name=SDS Palladium|date=12-10-2022}}</ref>
| NFPA-H = 0
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Palladium is a metal with low toxicity as conventionally measured (e.g. [[Median lethal dose|LD<sub>50</sub>]]). Recent research on the mechanism of palladium toxicity suggests high toxicity if measured on a longer timeframe and at the cellular level in the liver and kidney.<ref>{{cite journal |last1=Hosseini |first1=M.-J. |last2=Jafarian |first2=I. |last3=Farahani |first3=S. |last4=Khodadadi |first4=R. |last5=Tagavi |first5=S. H. |last6=Naserzadeh |first6=P. |last7=Mohammadi-Bardbori |first7=A. |last8=Arghavanifard |first8=N. |title=New mechanistic approach of inorganic palladium toxicity: impairment in mitochondrial electron transfer |journal=Metallomics |date=2016 |volume=8 |issue=2 |pages=252–259 |doi=10.1039/C5MT00249D |pmid=26739318 }}</ref> Mitochondria appear to have a key role in palladium toxicity via mitochondrial membrane potential collapse and depletion of the cellular glutathione (GSH) level. Until that recent work, it had been thought that palladium was poorly absorbed by the [[human body]] when [[ingested]]. Plants such as the [[water hyacinth]] are killed by low levels of palladium salts, but most other plants tolerate it, although tests show that, at levels above 0.0003%, growth is affected. High doses of palladium could be poisonous; tests on [[rodents]] suggest it may be [[carcinogenic]], though until the recent research cited above, no clear evidence indicated that the element harms humans.<ref>{{cite book |first=John |last=Emsley |title=Nature's Building Blocks: An A-Z Guide to the Elements |publisher=Oxford University Press |isbn=978-0-19-960563-7 |pages=384, 387 |date=2011}}</ref>
=== Precautions ===
Like other [[platinum-group metal]]s, bulk Pd is quite inert. Although [[contact dermatitis]] has been reported, data on the effects are limited. It has been shown that people with an allergic reaction to palladium also react to nickel, making it advisable to avoid the use of dental alloys containing palladium on those so allergic.<ref name="Kiel">{{cite journal |last1=Kielhorn |first1=Janet |last2=Melber |first2=Christine |last3=Keller |first3=Detlef |last4=Mangelsdorf |first4=Inge |title=Palladium – A review of exposure and effects to human health |journal=International Journal of Hygiene and Environmental Health |volume=205 |issue=6 |pages=417–32 |date=2002 |pmid=12455264 |doi=10.1078/1438-4639-00180 |bibcode=2002IJHEH.205..417K}}</ref><ref>{{cite book |pages=549–563 |chapter=Health Risk Potential of Palladium |chapter-url=https://books.google.com/books?id=OnNZqylS_Z8C&pg=PA549 |title=Palladium emissions in the environment: analytical methods, environmental assessment and health effects |first1=Fathi |last1=Zereini |first2=Friedrich |last2=Alt |publisher=Springer Science & Business |date=2006 |isbn=978-3-540-29219-7}}</ref><ref>{{cite journal |last1=Wataha |first1=J. C. |last2=Hanks |first2=C. T. |title=Biological effects of palladium and risk of using palladium in dental casting alloys |journal=Journal of Oral Rehabilitation |volume=23 |issue=5 |pages=309–20 |date=1996 |pmid=8736443 |doi=10.1111/j.1365-2842.1996.tb00858.x}}</ref><ref>{{cite journal |last1=Aberer |first1=Werner |last2=Holub |first2=Henriette |last3=Strohal |first3=Robert |last4=Slavicek |first4=Rudolf |title=Palladium in dental alloys – the dermatologists' responsibility to warn? |journal=Contact Dermatitis |volume=28 |issue=3 |pages=163–5 |date=1993 |pmid=8462294 |doi=10.1111/j.1600-0536.1993.tb03379.x }}</ref><ref>{{cite journal |last1=Wataha |first1=John C. |last2=Shor |first2=Kavita |title=Palladium alloys for biomedical devices |journal=Expert Review of Medical Devices |volume=7 |issue=4 |pages=489–501 |date=2010 |pmid=20583886 |doi=10.1586/erd.10.25 }}</ref>
Some palladium is emitted with the exhaust gases of cars with [[catalytic converter]]s. Between 4 and 108 ng/km of palladium particulate is released by such cars, while the total uptake from food is estimated to be less than 2 μg per person a day. The second possible source of palladium is dental restoration, from which the uptake of palladium is estimated to be less than 15 μg per person per day. People working with palladium or its compounds might have a considerably greater uptake. For soluble compounds such as [[palladium chloride]], 99% is eliminated from the body within three days.<ref name="Kiel" />
The [[median lethal dose]] (LD<sub>50</sub>) of soluble palladium compounds in mice is 200 mg/kg for [[oral administration|oral]] and 5 mg/kg for [[intravenous administration]].<ref name="Kiel" />
== History ==
[[File:Wollaston William Hyde Jackson color.jpg|thumb|upright|left|[[William Hyde Wollaston]]]]
[[File:Potw1749a Pallas crop.png|thumb|192x192px|[[Very Large Telescope]] image of [[2 Pallas]], the asteroid after which Palladium was named.]]
[[William Hyde Wollaston]] noted the [[discovery of the chemical elements|discovery]] of a new noble metal in July 1802 in his lab book and named it palladium in August of the same year. He named the element after the asteroid [[2 Pallas]], which had been discovered two months earlier (and which was [[List of former planets|previously considered a planet]]).<ref name="CRC" /> Wollaston purified a quantity of the material and offered it, without naming the discoverer, in a small shop in [[Soho]] in April 1803. After harsh criticism from [[Richard Chenevix (chemist)|Richard Chenevix]], who claimed that palladium was an alloy of platinum and mercury, Wollaston anonymously offered a reward of £20 for 20 grains of synthetic palladium ''alloy''.<ref name="contr">{{cite journal |doi=10.1080/00033797800200431 |title=The Wollaston/Chenevix controversy over the elemental nature of palladium: A curious episode in the history of chemistry |date=1978 |last1=Usselman |first1=Melvyn |journal=Annals of Science |volume=35 |issue=6 |pages=551–579}}</ref> Chenevix received the [[Copley Medal]] in 1803 after he published his experiments on palladium. Wollaston published the discovery of [[rhodium]] in 1804 and mentions some of his work on palladium.<ref name="Disco">{{cite journal |journal=Platinum Metals Review |title=Rhodium and Palladium – Events Surrounding Its Discovery |author=Griffith, W. P. |volume=47 |issue=4 |date=2003 |pages=175–183 |doi=10.1595/003214003X474175183 |doi-access=free}}</ref><ref>{{cite journal |title=On a New Metal, Found in Crude Platina |first=W. H. |last=Wollaston |author-link=William Hyde Wollaston |journal=[[Philosophical Transactions of the Royal Society of London]] |volume=94 |date=1804 |pages=419–430 |doi=10.1098/rstl.1804.0019 |url=https://books.google.com/books?id=7AZGAAAAMAAJ&pg=PA419 |doi-access=free}}</ref> He disclosed that he was the discoverer of palladium in a publication in 1805.<ref name="contr" /><ref>{{cite journal |title=On the Discovery of Palladium; With Observations on Other Substances Found with Platina |first=W. H. |last=Wollaston |author-link=William Hyde Wollaston |journal=[[Philosophical Transactions of the Royal Society of London]] |volume=95 |date=1805 |pages=316–330 |doi=10.1098/rstl.1805.0024 |doi-access=free}}</ref>
Wollaston found palladium in crude platinum ore from [[South America]] by dissolving the ore in [[aqua regia]], neutralizing the solution with [[sodium hydroxide]], and precipitating platinum as [[ammonium chloroplatinate]] with [[ammonium chloride]]. He added [[mercuric cyanide]] to form the compound [[palladium(II) cyanide]], which was heated to extract palladium metal.<ref name="Disco" />
[[Palladium chloride]] was at one time prescribed as a [[tuberculosis]] treatment at the rate of 0.065 g per day (approximately one milligram per kilogram of body weight). This treatment had many negative [[Adverse effect (medicine)|side-effects]], and was later replaced by more effective drugs.<ref>{{cite journal |title=The Art of Meeting Palladium Specifications in Active Pharmaceutical Ingredients Produced by Pd-Catalyzed Reactions |first=Christine E. |last=Garrett |author2=Prasad, Kapa |journal=Advanced Synthesis & Catalysis |volume=346 |issue=8 |date=2004 |pages=889–900 |doi=10.1002/adsc.200404071 }}</ref>
Most palladium is used for [[catalytic converter]]s in the automobile industry.<ref name="Kiel" /> Catalytic converters are targets for thieves because they contain palladium and other rare metals. In the run up to year 2000, the Russian supply of palladium to the global market was repeatedly delayed and disrupted; for political reasons, the export quota was not granted on time.<ref>{{cite web |url=http://www.lbma.org.uk/assets/5d_Williamson_lbmaconf2003.pdf |title=Russian PGM Stocks |last=Williamson |first=Alan |work=The LBMA Precious Metals Conference 2003 |publisher=The London Bullion Market Association |access-date=2 October 2010 |archive-date=21 October 2013 |archive-url=https://web.archive.org/web/20131021171646/http://www.lbma.org.uk/assets/5d_Williamson_lbmaconf2003.pdf |url-status=dead}}</ref> The ensuing market panic drove the price to an all-time high of {{convert|1340|$/ozt|$/g|lk=on}} in January 2001.<ref name="chart-all">{{cite web |url=http://www.infomine.com/investment/metal-prices/palladium/all/ |title=Historical Palladium Prices and Price Chart |access-date=2015-01-27 |publisher=InvestmentMine}}</ref> Around that time, the [[Ford Motor Company]], fearing that automobile production would be disrupted by a palladium shortage, stockpiled the metal. When prices fell in early 2001, Ford lost nearly [[US$]]1 billion.<ref>{{cite news |date=16 January 2002 |title=Ford fears first loss in a decade |work=BBC News |url=http://news.bbc.co.uk/1/hi/business/1763406.stm |access-date=19 September 2008}}</ref>
World demand for palladium increased from 100 tons in 1990 to nearly 300 tons in 2000. The global production of palladium from mines was 222 [[tonne]]s in 2006 according to the [[United States Geological Survey]].<ref name="USGS07CS">{{cite web |url=http://minerals.usgs.gov/minerals/pubs/commodity/platinum/platimcs07.pdf |title=Platinum-Group Metals |date=January 2007 |work=Mineral Commodity Summaries |publisher=[[United States Geological Survey]] |access-date=14 July 2007 |archive-date=9 July 2017 |archive-url=https://web.archive.org/web/20170709121002/https://minerals.usgs.gov/minerals/pubs/commodity/platinum/platimcs07.pdf |url-status=dead }}</ref> Many were concerned about a steady supply of palladium in the wake of Russia's [[Annexation of Crimea by the Russian Federation|annexation of Crimea]], partly as sanctions could hamper Russian palladium exports; any restrictions on Russian palladium exports could have exacerbated what was already expected to be a large palladium deficit in 2014.<ref>{{cite web |author=Nat Rudarakanchana |date=2014-03-27 |title=Palladium Fund Launches in South Africa, As Russian Supply Fears Warm Prices |url=http://www.ibtimes.com/palladium-fund-launches-south-africa-russian-supply-fears-warm-prices-1563708 |website=International Business Times}}</ref> Those concerns pushed palladium prices to their highest level since 2001.<ref>{{Cite news |url=https://www.cnbc.com/2014/08/20/palladium-prices-russia-conflict-pushes-price-for-commodity-higher.html |title=The other commodity that's leaping on Ukraine war |last=Rosenfeld |first=Everett |date=2014-08-20 |work=CNBC |access-date=2018-01-29}}</ref> In September 2014 they soared above the $900 per ounce mark. In 2016 however palladium cost around $614 per ounce as Russia managed to maintain stable supplies.<ref>{{Cite news |url=https://www.bloomberg.com/view/articles/2017-08-30/palladium-rally-is-about-more-than-just-autos |title=Palladium Rally Is About More Than Just Autos |date=2017-08-30 |work=Bloomberg.com |access-date=2018-01-29 |language=en}}</ref> In January 2019 palladium [[Futures contract|futures]] climbed past $1,344 per ounce for the first time on record, mainly due to the strong demand from the automotive industry.<ref>{{Cite web |url=https://oilprice.com/Metals/Commodities/Dont-Expect-Palladium-Prices-to-Plunge.html |title=Don't Expect Palladium Prices To Plunge {{!}} OilPrice.com |website=OilPrice.com |language=en |access-date=2018-01-29}}</ref> Palladium reached {{convert|2024.64|$/ozt|$/g}} on 6 January 2020, passing $2,000 per troy ounce the first time.<ref>{{Cite news |url=https://www.reuters.com/article/us-global-precious/gold-soars-as-middle-east-tensions-brew-perfect-storm-idUSKBN1Z50D9 |title=Gold soars as Middle East tensions brew perfect storm |newspaper=Reuters |language=en |access-date=2020-01-06 |date=6 January 2020}}</ref> The price rose above $3,000 per troy ounce in May 2021 and March 2022.<ref>{{Cite web |url=https://www.reuters.com/markets/europe/gold-gains-after-russia-attacks-europes-largest-nuclear-plant-2022-03-04/ |title=Palladium tops $3,000/oz as supply fears grow, gold jumps over 1% |first=Brijesh |last=Patel |date=4 March 2022 |website=[[Reuters]]}}</ref>
== Palladium as investment ==
[[File:Palladium Prices.webp|thumb|right|Palladium prices – US dollars per [[troy ounce]]]]
Global palladium sales were {{convert|8.84|e6ozt|t}} in 2017,<ref>{{Cite web |url=https://www.statista.com/statistics/418218/global-palladium-supply/ |title=Total palladium supply worldwide 2017 {{!}} Statistic |website=Statista |language=en |access-date=2018-10-15}}</ref> of which 86% was used in the manufacturing of automotive catalytic converters, followed by industrial, jewellery, and investment usages.<ref>{{Cite web |url=https://www.statista.com/statistics/254543/global-palladium-demand-by-sector/ |title=Global palladium demand distribution by application 2016 {{!}} Statistic |website=Statista |language=en |access-date=2018-10-15}}</ref> More than 75% of global platinum and 40% of palladium are mined in [[South Africa]]. Russia's mining company, [[Norilsk Nickel]], produces another 44% of palladium, with US and Canada-based mines producing most of the rest.
The price for palladium reached an all-time high of $2,981.40 per [[troy ounce]] on May 3, 2021,<ref>{{cite web |url=https://www.kitco.com/charts/historicalpalladium.html |title=Historical Palladium Charts and Data - London Fix}}</ref><ref>{{Cite web |url=https://data.bls.gov/cgi-bin/cpicalc.pl?cost1=1100&year1=200101&year2=201807 |title=CPI Inflation Calculator |website=data.bls.gov |access-date=2018-08-13}}</ref> driven mainly on speculation of the [[catalytic converter]] demand from the [[automobile industry]]. Over the following few years the price fell by over two-thirds. Palladium is traded in the [[spot market]] with the code "XPD". When settled in USD, the code is "XPDUSD". A later surplus of the metal was caused by the [[Russian government]] selling stockpiles from the [[Soviet era]], at a rate of about {{convert|1.6|to|2|e6ozt|t}} a year. The amount and status of this stockpile are a [[Classified information|state secret]].
=== Palladium producers ===
* [[Norilsk Nickel]]
* [[Sibanye-Stillwater]]
* [[Anglo American Platinum]]
* [[Impala Platinum]]
* [[Northam Platinum]]
=== Exchange-traded products ===
WisdomTree Physical Palladium ({{lse2|PHPD}}) is backed by allocated palladium [[bullion]] and was the world's first palladium [[Exchange-traded fund|ETF]]. It is listed on the [[London Stock Exchange]] as PHPD,<ref>{{cite web |url=http://www.londonstockexchange.com/exchange/prices-and-news/stocks/summary/company-summary.html?fourWayKey=JE00B1VS3002JEUSDETCS |title=ETFS METAL PAL ETP price (PHPD) |publisher=London Stock Exchange}}</ref> [[Xetra (trading system)|Xetra Trading System]], [[Euronext]] and [[Borsa Italiana|Milan]]. ETFS Physical Palladium Shares ({{nyse2|PALL}}) is an ETF traded on the [[New York Stock Exchange]].
=== Bullion coins and bars ===
{{see also|Palladium coin}}
A traditional way of investing in palladium is buying [[bullion coins]] and bars made of palladium. Available palladium coins include the [[Canadian Palladium Maple Leaf]], the [[Chinese panda coins|Chinese Panda]], and the [[American Palladium Eagle]]. The [[liquidity]] of direct palladium bullion investment is poorer than that of [[gold]], [[platinum]], and [[silver]] because there is a lower circulation of palladium coins than the big three precious metals.<ref>{{Cite web |title=Size of the Palladium Market {{!}} Sunshine Profits |url=https://www.sunshineprofits.com/gold-silver/dictionary/size-the-palladium-market/ |access-date=2023-02-11 |website=www.sunshineprofits.com}}</ref>
== See also ==
* [[2000s commodities boom]]
* [[2020s commodities boom]]
* [[Bullion]]
* [[Bullion coin]]
* [[Inflation hedge]]
* [[Pseudo palladium]]
* Rare materials as an [[investment]]:
** [[Silver as an investment]]
** [[Gold as an investment]]
** [[Platinum as an investment]]
** [[Diamonds as an investment]]
== References ==
{{reflist|30em}}
== External links ==
{{Commons|Palladium}}
{{Wiktionary|palladium}}
* <!--HTTP--->[http://www.periodicvideos.com/videos/046.htm Palladium] at ''[[The Periodic Table of Videos]]'' (University of Nottingham)
* [https://www.kitco.com/price/precious-metals/palladium Current and Historical Palladium Price]
* {{cite EB1911|wstitle=Palladium (chemistry) |display=Palladium |volume=20 |pages=636–637|short=x}}
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{{Periodic table (navbox)}}
{{Palladium compounds}}
{{Jewellery}}
{{Authority control}}
[[Category:Palladium| ]]
[[Category:Chemical elements]]
[[Category:Noble metals]]
[[Category:Transition metals]]
[[Category:Precious metals]]
[[Category:Native element minerals]]
[[Category:Chemical elements with face-centered cubic structure]]
[[Category:Platinum-group metals]]
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