Oxygen is important for the synthesis of
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Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as well as with other compounds. After hydrogen and helium, oxygen is the third-most abundant element in the universe by mass. At standard temperature and pressure, two atoms of the element bind to form dioxygen, a colorless and odorless diatomic gas with the formula O
2. Diatomic oxygen gas constitutes 20.95% of the Earth's atmosphere. Oxygen makes up almost half of the Earth's crust in the form of oxides.[2]
Dioxygen provides the energy released in combustion[3] and aerobic cellular respiration,[4] and many major classes of organic molecules in living organisms contain oxygen atoms, such as proteins, nucleic acids, carbohydrates, and fats, as do the major constituent inorganic compounds of animal shells, teeth, and bone. Most of the mass of living organisms is oxygen as a component of water, the major constituent of lifeforms. Oxygen is continuously replenished in Earth's atmosphere by photosynthesis, which uses the energy of sunlight to produce oxygen from water and carbon dioxide. Oxygen is too chemically reactive to remain a free element in air without being continuously replenished by the photosynthetic action of living organisms. Another form (allotrope) of oxygen, ozone (O
3), strongly absorbs ultraviolet UVB radiation and the high-altitude ozone layer helps protect the biosphere from ultraviolet radiation. However, ozone present at the surface is a byproduct of smog and thus a pollutant.
Oxygen was isolated by Michael Sendivogius before 1604, but it is commonly believed that the element was discovered independently by Carl Wilhelm Scheele, in Uppsala, in 1773 or earlier, and Joseph Priestley in Wiltshire, in 1774. Priority is often given for Priestley because his work was published first. Priestley, however, called oxygen "dephlogisticated air", and did not recognize it as a chemical element. The name oxygen was coined in 1777 by Antoine Lavoisier, who first recognized oxygen as a chemical element and correctly characterized the role it plays in combustion.
Common uses of oxygen include production of steel, plastics and textiles, brazing, welding and cutting of steels and other metals, rocket propellant, oxygen therapy, and life support systems in aircraft, submarines, spaceflight and diving.
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oxygen functionalized carbon nanotubes synthesized by surface acid treatment were used to improve the dispersion properties of active materials for catalysis. Carbon nanotubes have gained attention as a support for active materials due to their high specific surface areas (400–700 m2 g−1) and chemical stability. However, the lack of surface functionality causes poor dispersion of active materials on carbon nanotube supports. In this study, oxygen functional groups were prepared on the surface of carbon nanotubes as anchoring sites for decoration with catalytic nanoparticles. The oxygen functional groups were prepared through a chemical acid treatment using sulfuric acid and nitric acid, and the amount of functional groups was controlled by the reaction time. Vanadium, tungsten, and titanium oxides as catalytic materials were dispersed using an impregnation method on the synthesized carbon nanotube surfaces. Due to the high density of oxygen functional groups, the catalytic nanoparticles were well dispersed and reduced in size on the surface of the carbon nanotube supports. The selective catalytic reduction catalyst with the oxygen functionalized carbon nanotube support exhibited enhanced NOx removal efficiency of over 90% at 350–380 °C which is the general operating temperature range of catalysis in power plants.
Nitrogen oxides (NOx) are emitted from both stationary sources (power plants, cement, chemical plants, steel mills, etc.) and mobile sources (large vessels, automobiles) and exist in various forms such as NO, and NO2.11,12 NOx have been identified as the main source of fine particulate matter (PM2.5), and various studies have been conducted to reduce their emissions from the sources.13,14 Selective catalytic reduction (SCR) of NOx with NH3 is a representative NOx removal method that can reduce NOx emissions by 80–100%. In recent years, many researches have been conducted to improve the catalytic activity in an extended temperature range of SCR catalyst by adding the various catalysts components such as Fe, Ce, Mn and Cu.14 It was reported by Han et al. that the SCR catalyst having good sulfur-poisoning resistance was prepared by adding Fe2O3 to a support
Here, we synthesized oxygen functionalized CNTs (O-CNTs), and applied them in V–W/TiO2 SCR catalysts. An acid treatment process using sulfuric acid and nitric acid was conducted to functionalize the CNT surfaces with abundant oxygen functional groups, and the amount of functional groups was adjusted by controlling the acid treatment time. The vanadium, tungsten, and titanium oxide catalyst materials were well dispersed on the synthesized O-CNTs because the surface functional groups which acted as anchoring sites of catalyst materials, and they inhibited the aggregation of active materials and reduced the size of catalysts nanoparticles. As a result, the synthesized catalysts have enhanced catalytic acid sites and high specific surface area, and the NOx removal efficiency can be enhanced even with the less amounts of active materials.22
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