We combine both theoretical and experimental evidence to provide a new physical insight into the significant effect due to the defects induced by the Ce ion substitution on the catalytic activity of OMS The formation of unique Ce ion substituted OMS-2 nanostructure with Mn vacancies in the framework leads to a significant enhancement of the lattice oxygen activity, thus tremendously increasing the catalytic activity.
Hou, Y. Li, M. Mao, X. Zhao and Y. Yue, Nanoscale , , 6 , DOI: To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.
If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. Read more about how to correctly acknowledge RSC content. Fetching data from CrossRef. This may take some time to load. Loading related content. The name is derived from the Latin word for charcoal, carbo. It is found in the Earth's crust at a concentration of ppm, making it the 15th most abundant element.
It is found in form of calcium carbonate, CaCO 3 , in minerals such as limestone, marble, and dolomite a mixture of calcium and magnesium carbonate ; calcium carbonate also forms the shells of marine organisms and the coral of coral reefs.
Carbon is also found in coal, petroleum, and natural gas. Carbon is one of the most important elements on the periodic table at least from the perspective of organic chemists! Pure carbon is found in three stable forms at room temperature: graphite, diamond, and the fullerene form. In graphite, the carbon atoms are connected in sheets, which can slide past each other, which makes graphite able to act as a lubricant, and why it makes marks on paper in the form of pencil "lead.
Contrary to the James Bond title, diamonds aren't forever, since the graphite form is more stable; however, diamonds turn into graphite at an incredibly slow rate. Diamonds are so different in their physical characteristics from graphite or charcoal that it was not recognized the diamond was a form of carbons; this was shown by Antoine Lavoisier in when he demonstrated that both charcoal and diamond could be burned to produce carbon dioxide. Smithson Tennant confirmed this relationship in when he showed that equal amounts of charcoal and diamond produced equal amounts of carbon dioxide.
In the fullerene form, the carbon atoms are arranged in hollow balls, or in hollow tubes called "nanotubes" ; these forms of carbon have very interesting chemical physical properties, and are the subject of intense research by chemists and chemical engineers. Carbon is produced in stars by the triple alpha process, in which three alpha particles are converted into carbon In this process, two alpha particles helium nuclei, 4 2 He fuse to form beryllium-8, which then fuses with another alpha particle to produce carbon This process takes place in older stars where a lot of hydrogen has been converted into helium; the star collapses, raising the pressure and temperature in the core to above million Kelvins, initiating the process of helium burning.
Some ionic compounds of carbon are known, but carbon typically forms compounds through covalent bonding. Carbon forms strong, stable covalent bonds to other carbon atoms, and is capable of forming long chains containing anywhere from a few dozen carbon atoms to hundred of thousands of carbon atoms. Carbon can also form bonds to other elements, such as hydrogen, oxygen, nitrogen, sulfur, phosphorus, the halogens, etc. There are therefore a tremendous variety of complex carbon-based chemicals.
Organic chemistry is the field of chemistry concerned with the study of carbon-containing compounds. Such compounds form the basis of life at least the kinds that we know about. Carbon is found is coal, and petroleum is a very complex mixture of thousands of different hydrocarbons.
The burning of carbon and petroleum products fossil fuels provides most of the energy which we consume, and contributes to global warming through the release of carbon dioxide into the atmosphere. Carbon is used is the refining of iron and other metals the oxygen in the ores is carried away in the form of carbon dioxide, leaving behind the elemental metal.
Small amounts of carbon are added to iron to make an alloy called steel, which is harder than pure iron. Activated charcoal is a finely powdered form of carbon used to filter out impurities from water or gases. Carbon is taken up by green plants in the form of carbon dioxide, CO 2 ; in the process of photosynthesis, the carbon in the carbon dioxide is transformed into carbohydrates sugars , lipids, proteins, and all of the other organic molecules which are essential to life.
Most carbon is in the form of the carbon isotope Carbon, which is also non-radioactive, accounts for 1. In the Earth's crust, it is found at a concentration of ppm mostly in the form water and of organic compounds , making it the 10th most abundant element. Of course, there's also "dark matter" and "dark energy" to worry about, but that's another story. Hydrogen, helium, and trace amounts of lithium were produced at the beginning of the Universe in the Big Bang, and became concentrated into stars by the force of gravity.
The fusion of hydrogen and its isotopes see below also powers the hydrogen bomb, which contains lithium deuteride LiD and tritium; the explosion of a fission-powered bomb produces neutrons which initiate fusion of the deuterium with the tritium, releasing vast amounts of energy. Research into achieving controlled nuclear fusion to generate electricity is being conducted, but the extremely high temperatures that are necessary to initiate the fusion reactions present a major challenge to physicists.
Hydrogen typically does not form cations, but instead forms compounds through covalent bonding. Hydrogen can form bonds to many other elements, such as nitrogen NH 3 and its derivatives , oxygen H 2 O and sulfur H 2 S , the halogens HX , and carbon, where it is found in millions of different hydrocarbons and other organic molecules almost all organic molecules contain at least some hydrogen atoms.
Hydrogen can also bond to metal atoms, such as lithium LiH , calcium CaH 2 , etc. In these compounds, the bonding is usually pictured as a metal cation combined with a hydride anion H -.
On some periodic tables, in fact, hydrogen is placed at the top of Group 7A, since like the halogens, it can form a -1 charge. Hydrogen is also found in acids , which are molecules containing easily-removed hydrogen atoms, usually connected to oxygen, nitrogen, or a halogen.
This is a greatly oversimplified explanation of acid-base chemistry. Hydrogen was discovered by the English chemist Henry Cavendish in ; hydrogen had been observed before, but Cavendish was the first to recognize not only that it was an element, but that it burned to form water, which also provided conclusive proof that water was not itself an element.
The name "hydrogen" was derived by the French chemist Antoine Lavoisier from the Greek words hydro "water" and genes "forming". There are three isotopes of hydrogen. Hydrogen-1, or protium , contains one proton in its nucleus, and is by far the most common form of hydrogen Hydrogen-2, or deuterium , contains one proton and one neutron in its nucleus, and comprises the remaining 0.
Hydrogen-3, or tritium , contains one proton and two neutrons, and is only found in trace amounts; it is produced by the interaction of cosmic rays on gases in the upper atmosphere, and in nuclear explosions, but since it has a half life of only Heavy water is water made from two atoms of deuterium and one atom of oxygen. This form of water is literally heavier than "ordinary" water, since an atom of deuterium is twice as heavy as an atom of "regular" hydrogen. H 2 O has a molar mass of Ordinary water contains about 1 molecule of D 2 O for every molecules of H 2 O.
The electrolysis of water concentrates D 2 O in the solution, since the lighter isotope evaporates from the solution slightly faster.
Successive electrolysis experiments allow pure heavy water to be produced, but it takes about , gallons of water to produce 1 gallon of heavy water by this method. Heavy water is used as a moderator in nuclear reactions: it slows down fast-moving neutrons, allowing them to be captured more easily by other nuclei.
The generation of heavy water was important during the research on nuclear fission that went into the Manhattan Project during World War II.
For a typical person, a fatal dose would require drinking nothing but heavy water for 10 to 14 days, so it's pretty doubtful that heavy water poisoning will be featured on CSI anytime soon. Most hydrogen is prepared industrially be reacting coal or hydrocarbons with steam at high temperatures to produce carbon monoxide and hydrogen gas a mixture of carbon monoxide and hydrogen is called synthesis gas , and can be used in manufacturing methanol.
On smaller scales it can be produced by the reaction of active metals such as zinc, calcium, etc. Hydrogen gas is combined with nitrogen in the Haber process to synthesize ammonia NH 3 , which is widely used in fertilizers. It is also used in the manufacture of hydrogenated vegetable oils; in this reaction, hydrogen atoms add to the carbon-carbon double bonds in the vegetable oils double-bonded carbons bond to fewer hydrogen atoms than single-bonded carbons — i.
Another use for hydrogen is in rocket fuels: the Saturn V rockets that launched the Apollo lunar missions used , gallons of kerosene and , gallons of liquid oxygen in its first stage S-IC , , gallons of liquid hydrogen and 83, gallons of liquid oxygen in its second stage S-II , and 69, gallons of liquid hydrogen and 20, gallons of liquid oxygen in its third S-IVB stage; the Space Shuttle main engines use , gallons of liquid hydrogen and , gallons of liquid oxygen.
Hydrogen is lighter than air, and was used in balloons and dirigibles also known as airships or zeppelins. Dirigibles were used in city-to-city air travel in the early s, and in trans-Atlantic crossings in the s and s. During World War I, German zeppelins were used in bombing runs over England, since they could fly higher than the British planes. On May 6, , the German dirigible Hindenburg caught fire as it came in for a landing at Lakehurst Naval Air Station in New Jersey; 35 people out of the 97 aboard and one person on the ground were killed.
The exact cause of the fire is still the subject of speculation, but the disaster signaled the beginning of the end for airship travel. Modern "blimps" use helium to provide lift, which avoids the problem of hydrogen's flammability. Molecules which contain hydrogen bonded to nitrogen, oxygen, or fluorine can attract one another through the formation of hydrogen bonds. Hydrogen bonds are a particularly strong form of dipole-dipole forces , which arise because of the unequal sharing of electrons in some covalent bonds.
If one atom in a covalent bond is more electronegative than the other, it "pulls" harder on the electrons that the two atoms share, giving the more electronegative atom a partial negative charge, and the less electronegative atom a partial positive charge. The partially negative atom on one molecule attracts the partially positive atom on a neighboring molecule, causing the two molecules to be more attracted to each other than two nonpolar molecules which have no electronegativity differences between their bonded atoms would be.
Molecules that interact by these dipole-dipole forces tend to have higher boiling points than nonpolar molecules, because higher temperatures are necessary to overcome the attractive forces between the molecules and separate the molecules into the gas phase.
In the case of O—H, N—H, and F—H bonds, the electronegativity differences are particularly large because fluorine, oxygen, and nitrogen are the most strongly electronegative elements. The attractive forces between molecules containing these bonds are particularly strong, and are given the name hydrogen bonds. Hydrogen bonds are not as strong as covalent bonds, but they greatly influence the physical properties of many substances. In particular, hydrogen bonds are responsible for the fact that water is a liquid at temperatures at which molecules of similar molecular mass are gases.
For instance, hydrogen sulfide, H 2 S, which weighs Ice floats on liquid water because the hydrogen bonds hold the molecules into a more open, hexagonal array, causing the solid form to be less dense than the liquid form. In living systems, hydrogen bonding plays a crucial role in many biochemical process, from the coiling of proteins into complex three-dimensional forms to the structure of the DNA double helix, in which the two strands of DNA are held together by the hydrogen bonding between their nucleic acids components.
In this technique, a sample is placed in a powerful magnetic field usually produced by a superconducting magnet — see the section on Helium , which causes the hydrogen atoms in the sample to resonate between two different magnetic energy levels; pulsing the sample with a burst of radiofrequency radiation typically between to MHz causes the hydrogen atoms to absorb some of this radiation, producing a readout called an "NMR spectrum" which can be used to deduce a great deal of structural information about organic molecules.
Since almost all organic molecules contain hydrogen atoms, this technique is widely used by organic chemists to probe molecular structure; it can also be used to determine a great deal of information about extremely complex molecules such as proteins and DNA.
The technique is nondestructive, and only requires small amounts of sample.
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