Cerium(IV) oxide

Source: Wikipedia, the free encyclopedia.
For the other compound also known as cerium oxide, see Cerium(III) oxide.
Cerium(IV) oxide
Cerium(IV) oxide
Names
IUPAC name
Cerium(IV) oxide
Other names
Ceric oxide,
Ceria,
Cerium dioxide
Identifiers
3D model (
JSmol
)
ChEBI
ChemSpider
ECHA InfoCard
 100.013.774 Edit this at Wikidata
UNII
  • InChI=1S/Ce.2O/q+4;2*-2 checkY
    Key: OFJATJUUUCAKMK-UHFFFAOYSA-N checkY
  • InChI=1/Ce.2O/q+4;2*-2
    Key: OFJATJUUUCAKMK-UHFFFAOYAX
  • [O-2]=[Ce+4]=[O-2]
Properties
CeO2
Molar mass 172.115 g/mol
Appearance white or pale yellow solid,
slightly hygroscopic
Density 7.215 g/cm3
Melting point 2,400 °C (4,350 °F; 2,670 K)
Boiling point 3,500 °C (6,330 °F; 3,770 K)
insoluble
+26.0·10−6 cm3/mol
Structure
cubic crystal system, cF12 (fluorite)[1]
Fm3m, #225
a = 5.41 Å [2], b = 5.41 Å, c = 5.41 Å
α = 90°, β = 90°, γ = 90°
Ce, 8, cubic
O, 4, tetrahedral
Hazards
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 1: Exposure would cause irritation but only minor residual injury. E.g. turpentineFlammability 0: Will not burn. E.g. waterInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
1
0
0
Related compounds
Related compounds
 Cerium(III) oxide
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)

Cerium(IV) oxide, also known as ceric oxide, ceric dioxide, ceria, cerium oxide or cerium dioxide, is an

rare-earth metal cerium. It is a pale yellow-white powder with the chemical formula CeO2. It is an important commercial product and an intermediate in the purification of the element from the ores. The distinctive property of this material is its reversible conversion to a non-stoichiometric oxide
.

Production

bastnaesite and monazite. After extraction of the metal ions into aqueous base, Ce is separated from that mixture by addition of an oxidant followed by adjustment of the pH. This step exploits the low solubility of CeO2 and the fact that other rare-earth elements resist oxidation.[3]

Cerium(IV) oxide is formed by the calcination of cerium oxalate or cerium hydroxide.

Cerium also forms cerium(III) oxide, Ce
2O
3, which is unstable and will oxidize to cerium(IV) oxide.[4]

Structure and defect behavior

Cerium oxide adopts the

non-stoichiometric, anion deficient form that retains the fluorite lattice.[5] This material has the formula CeO(2−x), where 0 < x < 0.28.[6]
The value of x depends on both the temperature, surface termination and the oxygen partial pressure. The equation

has been shown to predict the equilibrium non-stoichiometry x over a wide range of oxygen partial pressures (103–10−4 Pa) and temperatures (1000–1900 °C).[7]

The non-stoichiometric form has a blue to black color, and exhibits both ionic and electronic conduction with ionic being the most significant at temperatures > 500 °C.[8]

The number of oxygen vacancies is frequently measured by using X-ray photoelectron spectroscopy to compare the ratio of Ce3+
to Ce4+
.

Defect chemistry

In the most stable fluorite phase of ceria, it exhibits several defects depending on partial pressure of oxygen or stress state of the material.[9][10][11][12]

The primary defects of concern are oxygen vacancies and small

solid-oxide fuel cells. Undoped and doped ceria also exhibit high electronic conductivity at low partial pressures of oxygen due to reduction of the cerium ion leading to the formation of small polarons
. Since the oxygen atoms in a ceria crystal occur in planes, diffusion of these anions is facile. The diffusion rate increases as the defect concentration increases.

The presence of oxygen vacancies at terminating ceria planes governs the energetics of ceria interactions with adsorbate molecules, and its wettability. Controlling such surface interactions is key to harnessing ceria in catalytic applications.[13]

Natural occurrence

Cerium(IV) oxide occurs naturally as the mineral

rare earth elements (REEs). Occurrence of cerianite-(Ce) is related to some examples of cerium anomaly, where Ce - which is oxidized easily - is separated from other REEs that remain trivalent and thus fit to structures of other minerals than cerianite-(Ce).[17][14][15]

Applications

Cerium has two main applications, which are listed below.

The principal industrial application of ceria is for polishing, especially

zirconia. For hobbyists, it is also known as "opticians' rouge".[18][19]

In its other main application, CeO2 is used to decolorize glass. It functions by converting green-tinted ferrous impurities to nearly colorless ferric oxides.[3]

Other niche and emerging applications

Catalysis

CeO2 has attracted much attention in the area of

water-gas shift reaction. It oxidizes carbon monoxide. Its reduced derivative Ce2O3 reduces water, with release of hydrogen.[20][21][22][23]

The interconvertibility of CeOx materials is the basis of the use of ceria for an oxidation catalyst. One small but illustrative use is its use in the walls of

self-cleaning ovens as a hydrocarbon oxidation catalyst during the high-temperature cleaning process. Another small scale but famous example is its role in oxidation of natural gas in gas mantles.[24]

white gas lantern mantle. The glowing element is mainly ThO2
doped with CeO2, heated by the Ce-catalyzed oxidation of the natural gas with air.

Building on its distinct surface interactions, ceria finds further use as a sensor in catalytic converters in automotive applications, controlling the air-exhaust ratio to reduce NOx and carbon monoxide emissions.[25]

Energy & fuels

Due to the significant

ionic and electronic conduction of cerium oxide, it is well suited to be used as a mixed conductor.[26] As such, cerium oxide is a material of interest for solid oxide fuel cells (SOFCs) in comparison to zirconium oxide.[27]

Thermochemically, the cerium(IV) oxide–cerium(III) oxide cycle or CeO2/Ce2O3 cycle is a two-step water splitting process that has been used for hydrogen production.[28] Because it leverages the oxygen vacancies between systems, this allows ceria in water to form hydroxyl (OH) groups.[29] The hydroxyl groups can then be released as oxygen oxidizes, thus providing a source of clean energy.

Optics

Cerium oxide has found use in infrared filters and as a replacement for thorium dioxide in incandescent mantles[30]

Welding

Cerium oxide is used as an addition to tungsten electrodes for Gas Tungsten Arc Welding. It provides advantages over pure Tungsten electrodes such as reducing electrode consumption rate and easier arc starting & stability. Ceria electrodes were first introduced in the US market in 1987, and are useful in AC, DC Electrode Positive, and DC Electrode Negative.

Safety aspects

Cerium oxide nanoparticles (nanoceria) have been investigated for their antibacterial and antioxidant activity.[31][32][33][34]

Nanoceria is a prospective replacement of zinc oxide and titanium dioxide in sunscreens, as it has lower photocatalytic activity.[35]

See also

References

  1. ISBN 0-07-049439-8
  2. ^ E. A. Kümmerle and G. Heger, “The Structures of C-Ce2O3+δ, Ce7O12, and Ce11O20,” Journal of Solid State Chemistry, vol. 147, no. 2, pp. 485–500, 1999.
  3. ^
    ISBN 978-3527306732
    ..
  4. ^ "Standard Thermodynamic Properties of Chemical Substances" (PDF). Archived from the original (PDF) on October 29, 2013.
  5. ^ DFT study of Cerium Oxide Surfaces Applied surface science 2019 vol 478
  6. ^ Defects and Defect Processes in Nonmetallic Solids By William Hayes, A. M. Stoneham Courier Dover Publications, 2004.
  7. hdl:2262/76279
    .
  8. ISBN 978-3-527-31156-9
    .
  9. S2CID 95469920
    .
  10. doi:10.1039/C3TA11752A
    .
  11. PMID 35528557
    .
  12. S2CID 204754299
    .
  13. S2CID 118895100
    .
  14. ^ a b "Cerianite-(Ce)". www.mindat.org. Retrieved 2020-11-12.
  15. ^ a b "List of Minerals". www.ima-mineralogy.org. 2011-03-21. Retrieved 2020-11-12.
  16. ^ Burke, Ernst (2008). "The use of suffixes in mineral names" (PDF). Elements. 4 (2): 96.
  17. S2CID 41920305
    .
  18. ^ "Properties of Common Abrasives (Boston Museum of Fine Arts)" (PDF).
  19. ^ "Ceric oxide - CAMEO". cameo.mfa.org.
  20. ^ Ruosi Peng; et a. (2018). "Size effect of Pt nanoparticles on the catalytic oxidation of toluene over Pt/CeO2 catalysts". Applied Catalysis B: Environmental. 220.
  21. PMID 27120134
    .
  22. PMID 23651311
    .
  23. doi:10.1002/aic.12234
    .
  24. ISBN 978-0-08-037941-8
    .
  25. doi:10.1016/j.cattod.2010.12.044
    .
  26. ^ "Mixed conductors". Max Planck institute for solid state research. Retrieved 16 September 2016.
  27. doi:10.1016/S0167-2738(98)00540-2
    .
  28. ^ "Hydrogen production from solar thermochemical water splitting cycles". SolarPACES. Archived from the original on August 30, 2009.
  29. ^ "New discoveries made on the role of Cerium Oxide in Hydrogen production". Ceric. 2018-07-01. Retrieved 2022-09-22.
  30. ^ "Cerium dioxide". DaNa. Archived from the original on 2013-03-02.
  31. PMID 29234605
    .
  32. PMID 20617106
    .
  33. PMID 29234605
    .
  34. PMID 22717232
    .
  35. PMID 20926307
    .

External links

Wikimedia Commons has media related to Cerium(IV) oxide.
Retrieved from "https://en.wikipedia.org/w/index.php?title=Cerium(IV)_oxide&oldid=1181271444"