Cerium(IV) oxide-cerium(III) oxide cycle
Encyclopedia
The cerium oxide–cerium(III) oxide cycle or CeO2/Ce2O3 cycle is a two step thermochemical
process based on cerium(IV) oxide
and cerium(III) oxide
for hydrogen production
. Advantage of the cerium
based cycle is the separation of H2 and O2 in two steps which makes high temperature gas separation redundant.
process (thermochemical cycle
) uses redox
systems:
For the first endothermic
step, cerium(IV) oxide is thermally dissociated
in an inert gas
atmosphere at 2000 °C (3,632 °F) and 100-200 milli-bar
into cerium(III) oxide and oxygen. In the second exothermic
step cerium(III) oxide reacts at 400 °C (752 °F)–600 °C (1,112 °F) in a fixed bed reactor with water and produces hydrogen
and cerium(IV) oxide.
Thermochemistry
Thermochemistry is the study of the energy and heat associated with chemical reactions and/or physical transformations. A reaction may release or absorb energy, and a phase change may do the same, such as in melting and boiling. Thermochemistry focuses on these energy changes, particularly on the...
process based on cerium(IV) oxide
Cerium(IV) oxide
Cerium oxide, also known as ceric oxide, ceria, cerium oxide or cerium dioxide, is an oxide of the rare earth metal cerium...
and cerium(III) oxide
Cerium(III) oxide
Cerium oxide is an oxide of the rare earth metal cerium. It has chemical formula Ce2O3, and is gold-yellow in color.-Exhaust catalysts:...
for hydrogen production
Hydrogen production
Hydrogen production is the family of industrial methods for generating hydrogen. Currently the dominant technology for direct production is steam reforming from hydrocarbons. Many other methods are known including electrolysis and thermolysis...
. Advantage of the cerium
Cerium
Cerium is a chemical element with the symbol Ce and atomic number 58. It is a soft, silvery, ductile metal which easily oxidizes in air. Cerium was named after the dwarf planet . Cerium is the most abundant of the rare earth elements, making up about 0.0046% of the Earth's crust by weight...
based cycle is the separation of H2 and O2 in two steps which makes high temperature gas separation redundant.
Process description
The thermochemical two-step water splittingWater splitting
Water splitting is the general term for a chemical reaction in which water is separated into oxygen and hydrogen. Efficient and economical water splitting would be a key technology component of a hydrogen economy. Various techniques for water splitting have been issued in water splitting patents in...
process (thermochemical cycle
Thermochemical cycle
Thermochemical cycles combine solely heat sources with chemical reactions to split water into its hydrogen and oxygen components . The term cycle is used because aside of water, hydrogen and oxygen, the chemical compounds used in these processes are continuously recycled.If work is partially used...
) uses redox
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
systems:
- DissociationDissociation (chemistry)Dissociation in chemistry and biochemistry is a general process in which ionic compounds separate or split into smaller particles, ions, or radicals, usually in a reversible manner...
: 2CeO2Cerium(IV) oxideCerium oxide, also known as ceric oxide, ceria, cerium oxide or cerium dioxide, is an oxide of the rare earth metal cerium...
→ Ce2O3Cerium(III) oxideCerium oxide is an oxide of the rare earth metal cerium. It has chemical formula Ce2O3, and is gold-yellow in color.-Exhaust catalysts:...
+ 0.5 O2
- HydrolysisHydrolysisHydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...
: Ce2O3Cerium(III) oxideCerium oxide is an oxide of the rare earth metal cerium. It has chemical formula Ce2O3, and is gold-yellow in color.-Exhaust catalysts:...
+ H2O → 2CeO2Cerium(IV) oxideCerium oxide, also known as ceric oxide, ceria, cerium oxide or cerium dioxide, is an oxide of the rare earth metal cerium...
+ H2HydrogenHydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
For the first endothermic
Endothermic
In thermodynamics, the word endothermic describes a process or reaction in which the system absorbs energy from the surroundings in the form of heat. Its etymology stems from the prefix endo- and the Greek word thermasi,...
step, cerium(IV) oxide is thermally dissociated
Thermal decomposition
Thermal decomposition, or thermolysis, is a chemical decomposition caused by heat. The decomposition temperature of a substance is the temperature at which the substance chemically decomposes....
in an inert gas
Inert gas
An inert gas is a non-reactive gas used during chemical synthesis, chemical analysis, or preservation of reactive materials. Inert gases are selected for specific settings for which they are functionally inert since the cost of the gas and the cost of purifying the gas are usually a consideration...
atmosphere at 2000 °C (3,632 °F) and 100-200 milli-bar
Bar (unit)
The bar is a unit of pressure equal to 100 kilopascals, and roughly equal to the atmospheric pressure on Earth at sea level. Other units derived from the bar are the megabar , kilobar , decibar , centibar , and millibar...
into cerium(III) oxide and oxygen. In the second exothermic
Exothermic
In thermodynamics, the term exothermic describes a process or reaction that releases energy from the system, usually in the form of heat, but also in the form of light , electricity , or sound...
step cerium(III) oxide reacts at 400 °C (752 °F)–600 °C (1,112 °F) in a fixed bed reactor with water and produces hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
and cerium(IV) oxide.
See also
- Copper–chlorine cycle
- HeliostatHeliostatA heliostat is a device that includes a mirror, usually a plane mirror, which turns so as to keep reflecting sunlight toward a predetermined target, compensating for the sun's apparent motions in the sky. The target may be a physical object, distant from the heliostat, or a direction in space...
- Hybrid sulfur cycleHybrid sulfur cycleThe hybrid sulfur cycle is a two-step water-splitting process intended to be used for hydrogen production. Based on sulfur oxidation and reduction, it is classified as a hybrid thermochemical cycle because it uses an electrochemical reaction for one of the two steps...
- Hydrosol-2Hydrosol-2HYDROSOL is series of European Union funded projects for the promotion of renewable energy...
- Iron oxide cycleIron oxide cycleThe iron oxide cycle is a two-step thermochemical cycle proposed for use for hydrogen production.-Process description:The thermochemical two-step water splitting process uses redox systems...
- Solar thermal energySolar thermal energySolar thermal energy is a technology for harnessing solar energy for thermal energy . Solar thermal collectors are classified by the United States Energy Information Administration as low-, medium-, or high-temperature collectors. Low-temperature collectors are flat plates generally used to heat...
- Sulfur–iodine cycle
- Zinc–zinc oxide cycle