Nitrogen fixationNitrogen fixation is a chemical process by which molecular nitrogen (N2), which has a strong triple covalent bond, is converted into ammonia (NH3) or related nitrogenous compounds, typically in soil or aquatic systems but also in industry. The nitrogen in air is molecular dinitrogen, a relatively nonreactive molecule that is metabolically useless to all but a few microorganisms. Biological nitrogen fixation or diazotrophy is an important microbe-mediated process that converts dinitrogen (N2) gas to ammonia (NH3) using the nitrogenase protein complex (Nif).
Asymmetric hydrogenationAsymmetric hydrogenation is a chemical reaction that adds two atoms of hydrogen to a target (substrate) molecule with three-dimensional spatial selectivity. Critically, this selectivity does not come from the target molecule itself, but from other reagents or catalysts present in the reaction. This allows spatial information (what chemists refer to as chirality) to transfer from one molecule to the target, forming the product as a single enantiomer.
Density functional theoryDensity-functional theory (DFT) is a computational quantum mechanical modelling method used in physics, chemistry and materials science to investigate the electronic structure (or nuclear structure) (principally the ground state) of many-body systems, in particular atoms, molecules, and the condensed phases. Using this theory, the properties of a many-electron system can be determined by using functionals, i.e. functions of another function. In the case of DFT, these are functionals of the spatially dependent electron density.
Nitrogen cycleThe nitrogen cycle is the biogeochemical cycle by which nitrogen is converted into multiple chemical forms as it circulates among atmospheric, terrestrial, and marine ecosystems. The conversion of nitrogen can be carried out through both biological and physical processes. Important processes in the nitrogen cycle include fixation, ammonification, nitrification, and denitrification. The majority of Earth's atmosphere (78%) is atmospheric nitrogen, making it the largest source of nitrogen.
Transfer hydrogenationIn chemistry, transfer hydrogenation is a chemical reaction involving the addition of hydrogen to a compound from a source other than molecular . It is applied in laboratory and industrial organic synthesis to saturate organic compounds and reduce ketones to alcohols, and imines to amines. It avoids the need for high-pressure molecular used in conventional hydrogenation. Transfer hydrogenation usually occurs at mild temperature and pressure conditions using organic or organometallic catalysts, many of which are chiral, allowing efficient asymmetric synthesis.
NitrogenNitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at seventh in total abundance in the Milky Way and the Solar System. At standard temperature and pressure, two atoms of the element bond to form N2, a colorless and odorless diatomic gas. N2 forms about 78% of Earth's atmosphere, making it the most abundant uncombined element in air.
HydrogenationHydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a catalyst such as nickel, palladium or platinum. The process is commonly employed to reduce or saturate organic compounds. Hydrogenation typically constitutes the addition of pairs of hydrogen atoms to a molecule, often an alkene. Catalysts are required for the reaction to be usable; non-catalytic hydrogenation takes place only at very high temperatures.
Hydrogen storageSeveral methods exist for storing hydrogen. These include mechanical approaches such as using high pressures and low temperatures, or employing chemical compounds that release H2 upon demand. While large amounts of hydrogen are produced by various industries, it is mostly consumed at the site of production, notably for the synthesis of ammonia. For many years hydrogen has been stored as compressed gas or cryogenic liquid, and transported as such in cylinders, tubes, and cryogenic tanks for use in industry or as propellant in space programs.
AmmoniaAmmonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous waste, particularly among aquatic organisms, and it contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to 45% of the world's food and fertilizers. Around 70% of ammonia is used to make fertilisers in various forms and composition, such as urea and diammonium phosphate.
Binding energyIn physics and chemistry, binding energy is the smallest amount of energy required to remove a particle from a system of particles or to disassemble a system of particles into individual parts. In the former meaning the term is predominantly used in condensed matter physics, atomic physics, and chemistry, whereas in nuclear physics the term separation energy is used. A bound system is typically at a lower energy level than its unbound constituents.
Ammonia productionAmmonia production takes place worldwide, mostly in large-scale manufacturing plants that produce 235 million tonnes of ammonia (2021) annually. Leading producers are China (31.9%), Russia (8.7%), India (7.5%), and the United States (7.1%). 80% or more of ammonia is used as fertilizer. Ammonia is also used for the production of plastics, fibres, explosives, nitric acid (via the Ostwald process), and intermediates for dyes and pharmaceuticals. The industry contributes 1% to 2% of global CO2.
Wöhler synthesisThe Wöhler synthesis is the conversion of ammonium cyanate into urea. This chemical reaction was described in 1828 by Friedrich Wöhler. It is often cited as the starting point of modern organic chemistry. Although the Wöhler reaction concerns the conversion of ammonium cyanate, this salt appears only as an (unstable) intermediate. Wöhler demonstrated the reaction in his original publication with different sets of reactants: a combination of cyanic acid and ammonia, a combination of silver cyanate and ammonium chloride, a combination of lead cyanate and ammonia and finally from a combination of mercury cyanate and cyanatic ammonia (which is again cyanic acid with ammonia).
Liquid hydrogenLiquid hydrogen (H2(l)) is the liquid state of the element hydrogen. Hydrogen is found naturally in the molecular H2 form. To exist as a liquid, H2 must be cooled below its critical point of 33 K. However, for it to be in a fully liquid state at atmospheric pressure, H2 needs to be cooled to . A common method of obtaining liquid hydrogen involves a compressor resembling a jet engine in both appearance and principle. Liquid hydrogen is typically used as a concentrated form of hydrogen storage.
Hydrogen technologiesHydrogen technologies are technologies that relate to the production and use of hydrogen as a part hydrogen economy. Hydrogen technologies are applicable for many uses. Some hydrogen technologies are carbon neutral and could have a role in preventing climate change and a possible future hydrogen economy. Hydrogen is a chemical widely used in various applications including ammonia production, oil refining and energy. The most common methods for producing hydrogen on an industrial scale are: Steam reforming, oil reforming, coal gasification, water electrolysis.
Nuclear binding energyNuclear binding energy in experimental physics is the minimum energy that is required to disassemble the nucleus of an atom into its constituent protons and neutrons, known collectively as nucleons. The binding energy for stable nuclei is always a positive number, as the nucleus must gain energy for the nucleons to move apart from each other. Nucleons are attracted to each other by the strong nuclear force. In theoretical nuclear physics, the nuclear binding energy is considered a negative number.
Electron densityElectron density or electronic density is the measure of the probability of an electron being present at an infinitesimal element of space surrounding any given point. It is a scalar quantity depending upon three spatial variables and is typically denoted as either or . The density is determined, through definition, by the normalised -electron wavefunction which itself depends upon variables ( spatial and spin coordinates). Conversely, the density determines the wave function modulo up to a phase factor, providing the formal foundation of density functional theory.
Local-density approximationLocal-density approximations (LDA) are a class of approximations to the exchange–correlation (XC) energy functional in density functional theory (DFT) that depend solely upon the value of the electronic density at each point in space (and not, for example, derivatives of the density or the Kohn–Sham orbitals). Many approaches can yield local approximations to the XC energy. However, overwhelmingly successful local approximations are those that have been derived from the homogeneous electron gas (HEG) model.
AtomAn atom is a particle that consists of a nucleus of protons and neutrons surrounded by a cloud of electrons. The atom is the basic particle of the chemical elements, and the chemical elements are distinguished from each other by the number of protons that are in their atoms. For example, any atom that contains 11 protons is sodium, and any atom that contains 29 protons is copper. The number of neutrons defines the isotope of the element. Atoms are extremely small, typically around 100 picometers across.
Cracking (chemistry)In petrochemistry, petroleum geology and organic chemistry, cracking is the process whereby complex organic molecules such as kerogens or long-chain hydrocarbons are broken down into simpler molecules such as light hydrocarbons, by the breaking of carbon-carbon bonds in the precursors. The rate of cracking and the end products are strongly dependent on the temperature and presence of catalysts. Cracking is the breakdown of a large hydrocarbons into smaller, more useful alkanes and alkenes.
Ionization energyIn physics and chemistry, ionization energy (IE) (American English spelling), ionisation energy (British English spelling) is the minimum energy required to remove the most loosely bound electron of an isolated gaseous atom, positive ion, or molecule. The first ionization energy is quantitatively expressed as X(g) + energy ⟶ X+(g) + e− where X is any atom or molecule, X+ is the resultant ion when the original atom was stripped of a single electron, and e− is the removed electron.
