In 1903 Carl Auer von Welsbach unveiled ferrocerium — an alloy that relies on cerium to throw hot sparks for lighters — and that practical invention still tells you everything you need to know about this metal: cerium is unusually reactive for a lanthanide. Atomic number 58, cerium is the most abundant rare earth in the crust at roughly 66 ppm, and those electrons that toggle between +3 and +4 give it chemical flexibility that shows up in everyday tech from lighter flints to catalytic converters.
You should care because cerium’s reactions underpin products you use and technologies aimed at cleaner air: oxygen storage in catalysts, ceria polishing powders for optics, and ferrocerium for ignition are all downstream effects of how cerium interacts with other elements. This piece promises a focused look at eight specific elements cerium reacts with, how those reactions proceed, and why they matter.
Below we’ll walk through those eight elements and the practical chemistry they produce, starting with the gases and oxidizers that define cerium’s most important behavior.
Reactions with Gases and Oxidizers
Cerium’s chemistry is dominated by its ready shift between Ce3+ and Ce4+, which makes interactions with gases especially important. Oxidation and reduction change surface chemistry and bulk phases, so oxygen, water (or steam) and nitrogen are all notable partners for forming oxides, hydroxides or nitrides that matter industrially.
In practical terms, that redox flexibility gives cerium oxygen storage capacity in mixed oxides, and it explains why finely divided cerium behaves very differently from a polished lump of the metal.
1. Oxygen
Cerium oxidizes readily to Ce2O3 or the more common and stable CeO2 depending on temperature and oxygen partial pressure. CeO2 (cerium dioxide, commonly called ceria) is the oxide most people encounter in industry.
Ceria’s ability to switch between Ce4+ and Ce3+ makes it an oxygen reservoir, which is why ceria-zirconia mixed oxides are standard washcoats in automotive catalytic converters: they release or store oxygen to keep oxidation and reduction reactions balanced across changing exhaust conditions.
Other uses include ceria abrasives for glass and lens polishing and as a support or active phase in solid-oxide fuel cells and oxidation catalysts.
2. Water (and Steam)
Cerium reacts with water in ways that depend on its physical form and temperature. Bulk cerium generally tarnishes slowly in moist air as surface oxides and hydroxides form, but fine powders or filings oxidize much faster and can ignite when hot or finely divided.
At elevated temperatures — think a few hundred degrees Celsius and up toward the metal’s melting point (~798 °C) — steam can convert cerium metal to CeO2 while liberating hydrogen. That means machining, melting or processing cerium-containing alloys requires dry, controlled atmospheres and appropriate safeguards.
Laboratory demonstrations often show cerium filings burning in air or reacting vigorously when introduced to an oxidizing steam environment; industrially, this behaviour informs handling and protective atmospheres for metallurgical work.
3. Nitrogen
Cerium can form nitrides like CeN when heated in nitrogen or ammonia atmospheres. Nitridation is not a casual ambient reaction — it requires controlled, high-temperature conditions (hundreds to low thousands of degrees Celsius) and often a reducing environment to favor nitride formation over oxide.
Cerium nitrides are refractory and are studied for hard, high-temperature ceramics, thin-film electronic behavior and basic materials research rather than for broad commercial use. Typical lab syntheses heat cerium metal or cerium-containing precursors under flowing nitrogen or ammonia to produce CeN phases for study.
Halogens and Chalcogens: Reactive Nonmetals
Halogens and chalcogens form well-defined binary compounds with cerium. Fluorine and chlorine give halides such as CeF3 and CeCl3, while sulfur yields sulfides like CeS. These products are made under controlled conditions and have uses that range from optical materials to precursors in synthesis.
Handle halogen chemistry with care — fluorine in particular reacts violently and is reserved for equipped labs. Chlorination and sulfuration are more routine in inorganic synthesis and materials processing.
4. Fluorine
Elemental fluorine attacks cerium vigorously to form cerium fluorides such as CeF3. Fluorination is highly exothermic and is carried out only in specialized setups with corrosion-resistant equipment and strict safety protocols.
CeF3 and related fluorides appear in niche optical materials and as precursors in advanced materials chemistry. Laboratories produce CeF3 crystals by reacting cerium compounds with fluorine sources under controlled temperatures and flows.
Because fluorine gas and many fluorination reagents are hazardous, these syntheses are confined to well-equipped labs with appropriate training and containment.
5. Chlorine
Cerium reacts with chlorine to yield cerium(III) chloride (CeCl3) under moderate conditions. CeCl3 is a common, stable salt used as a reagent and as a gateway to other cerium compounds.
Syntheses can involve direct chlorination of the metal or reduction of CeO2 in the presence of chlorine at elevated temperatures. In organic chemistry CeCl3 serves as a Lewis acid or as a precursor to catalyst systems.
Because halide chemistry is a robust route to many cerium derivatives, CeCl3 often appears in labs when researchers prepare more complex cerium-containing materials.
6. Sulfur
Cerium reacts with sulfur vapor at high temperature to form sulfides such as CeS and more complex phases. These reactions are typical for lanthanides when heated with sulfur and produce compounds with distinct electronic and thermal properties.
Sulfide phases are mainly of research interest; they show up in studies probing lanthanide electronic structures, thermoelectric behavior and high-temperature materials. In practice, CeS is made in tube furnaces under sulfur-rich atmospheres for controlled synthesis.
While sulfur reactions aren’t common at room temperature, they matter during high-temperature processing where sulfur contamination or intentional sulfidation can change material performance.
Carbides, Silicides and Carbon-Based Reactions
At very high temperatures cerium forms interstitial and intermetallic compounds with carbon and silicon: carbides and silicides. These are solid-state products that change hardness, thermal stability and electronic behavior and are relevant to refractory materials and thin-film work.
These reactions generally need temperatures in the hundreds to thousands of degrees Celsius and controlled atmospheres or vacuum; they’re specialist processes rather than ambient chemistry, but they matter for metallurgical and materials problems.
7. Carbon (Carbides)
Cerium can form carbide phases such as dicarbides (LnC2-type) when reacted with carbon at high temperatures. Many lanthanides produce LnC2 or Ln2C3 phases depending on stoichiometry and synthesis route.
Typical syntheses use arc-melting, RF furnaces or high-temperature tube furnaces to drive carbon into the metal lattice and form CeC2. These carbides are studied for refractory applications and as experimental components in ceramics research.
Carbide formation affects mechanical and thermal properties and is something to watch for during high-temperature processing of cerium-containing alloys or composites.
8. Silicon (Silicides)
Cerium reacts with silicon to form silicides such as CeSi2 under high-temperature or vapor-deposition conditions. Intermetallic Ce–Si phases are a common outcome when lanthanides meet silicon substrates or when silicon is present during alloy processing.
Silicides form via solid-state reaction, thin-film deposition or diffusion at elevated temperatures, and they can alter electrical contacts, thermal transport and surface chemistry on silicon wafers or in metallurgical parts.
Thin-film experiments where cerium is deposited on silicon often report Ce–Si intermetallics, and in alloy contexts silicon contamination can unintentionally produce silicide phases that change performance.
Summary
- Cerium’s readiness to switch between +3 and +4 oxidation states drives its reactions with oxygen, water/steam and other oxidizers, underpinning technologies like catalytic converters and glass polishing.
- The eight elements covered — oxygen, water/steam, nitrogen, fluorine, chlorine, sulfur, carbon and silicon — yield oxides, hydroxides, nitrides, halides, sulfides, carbides and silicides that are useful in industry and research.
- Many of these reactions require elevated temperatures or fine powdered metal; powdered cerium and filings are far more reactive than bulky, polished pieces, so handle them with proper controls.
- Practical examples tie the chemistry to everyday tech: ferrocerium (1903) for ignition and ceria (CeO2) in automotive catalysts show how elemental reactions become products.
- If you work with cerium, follow lab safety for finely divided metals and halogen chemistry, and factor these reactions into materials selection for high-temperature or corrosive environments.
