Catalyst

A catalyst is a substance which alters the rate of a chemical reaction but is chemically unchanged at the end of the reaction. The Haber process, also called the Haber–Bosch process, is the nitrogen fixation reaction of nitrogen and hydrogen, over an enriched iron catalyst, to produce ammonia.[1][2][3][4] The Haber process is important because ammonia is difficult to produce on an industrial scale, and the fertilizer generated from the ammonia is responsible for sustaining one-third of the Earth's population.[5] Even though 78.1% of the air we breathe is nitrogen, the gas is relatively unreactive because nitrogen molecules are held together by strong triple bonds. It was not until the early 20th century that this method was developed to harness the atmospheric abundance of nitrogen to create ammonia, which can then be oxidized to make the nitrates and nitrites essential for the production of nitrate fertilizer and munitions.

Hydrogenation is the chemical reaction that results in addition of hydrogen (H2). The process is usually employed to a reduce or saturate organic compounds. The process typically constitutes the addition of pairs of hydrogen atoms to a molecule. Catalysts are required for the reaction to be usable; non-catalytic hydrogenation takes place only at very high temperatures. Hydrogen adds to double and triple bonds in hydrocarbons. [1] Because of the importance of hydrogen, many related reactions have been developed for its use. Most hydrogenations use gaseous hydrogen (H2), but some involve the alternative sources of hydrogen, not H2: these processes are called transfer hydrogenations. The reverse reaction, removal of hydrogen from a molecule, is called dehydrogenation. A reaction where bonds are broken while hydrogen is added is called hydrogenolysis, a reaction that may occur to carbon-carbon and carbon-heteroatom (O, N, X) bonds. Hydrogenation differs from protonation or hydride addition: in hydrogenation, the products have the same charge as the reactants. An illustrative example of a hydrogenation reaction is the addition of hydrogen to maleic acid to succinic acid depicted on the right.[2] Numerous important applications are found in the petrochemical, pharmaceutical and food industries. Hydrogenation of unsaturated fats produces saturated fats and, in some cases, trans fats The Ostwald process is a chemical process for producing nitric acid, which was developed by Wilhelm Ostwald (patented 1902). It is a mainstay of the modern chemical industry. Historically and practically it is closely associated with the Haber process, which provides the requisite raw material, ammonia. Ammonia is converted to nitric acid in two stages. It is oxidized (in a sense "burnt") by heating with oxygen in the presence of a catalyst such as platinum with 10% rhodium, to

form nitric oxide and water. This step is strongly exothermic, making it a useful heat source once initiated (ΔH = -908 kJ): 4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g) Stage two (combining two reaction steps) is carried out in the presence of water in an absorption apparatus. Initially nitric oxide is oxidized again to yield nitrogen dioxide: 2NO(g) + O2(g) → 2NO2(g) This gas is then readily absorbed by the water, yielding the desired product (nitric acid, albeit in a dilute form), while reducing a portion of it back to nitric oxide: 3NO2(g) + H2O(l) → 2HNO3(aq) + NO(g) The NO is recycled, and the acid is concentrated to the required strength by distillation. Alternatively, if the last step is carried out in air: 4NO2(g) + O2(g) + 2H2O(l) → 4HNO3(aq) Typical conditions for the first stage, which contribute to an overall yield of about 96%, are: • •

pressure between 4 and 10 atmospheres (approx. 400-1010 kPa or 60-145 psig) and temperature is about 1173 K (approx. 900 °C or 1652 °F.).