Iron catalysts Haber process

An even more effective homogeneous hydrogenation catalyst is the complex [RhClfPPhsfs] which permits rapid reduction of alkenes, alkynes and other unsaturated compounds in benzene solution at 25°C and 1 atm pressure (p. 1134). The Haber process, which uses iron metal catalysts for the direct synthesis of ammonia from nitrogen and hydrogen at high temperatures and pressures, is a further example (p. 421). 

The reactant is adsorbed on the catalyst s surface. As a reactant molecule attaches to the surface of the catalyst, its bonds are weakened and the reaction can proceed more quickly because the bonds are more easily broken (Fig. 13.36). One important step in the reaction mechanism of the Haber process for the synthesis of ammonia is the adsorption of N2 molecules on the iron catalyst and the weakening of the strong N=N triple bond. 

Invented in 1909 by Fritz Haber (1868-1934), the Haber-Bosch process requires very high pressure (250 atmospheres) and a temperature of approximately 932°F (500°C). The reaction also requires a porous iron catalyst. 

Industrially, ammonia has been produced from dinitrogen and dihydrogen by the Haber-Bosch process, which operates at very high temperatures and pressures, and utilizes a promoted iron catalyst. Millions of tons of ammonia are generated annually for incorporation into agricultural fertilizers and other important commercial products. The overall reaction is exergonic, as indicated in equation 6.1 ... 

A heterogeneous catalyst is in a different phase or state of matter than the reactants. Most commonly, the catalyst is a solid and the reactants are liquids or gases. These catalysts provide a surface for the reaction. The reactant on the surface is more reactive than the free molecule. Many times these homogeneous catalysts are finely divided metals. Chemists use an iron catalyst in the Haber process, which converts nitrogen and hydrogen gases into ammonia. The automobile catalytic converter is another example. 

The most important uses of synthesis gas are the manufacture of ammonia (NH3) via the Haber process. A mixture of nitrogen and hydrogen are passed over an iron catalyst (with aluminum oxide present as a "promoter"). The operating conditions are extreme—800°F and 4000 psi,... 

Transition metals and their compounds are used as catalysts. Catalysts you may already know are Iron In the Haber process (Industrial production of ammonia) platinum in the Ostwald process (Industrial production of nitric acid) and platinum, rhodium and palladium In catalytic converters. 

Fig. 4.1 outlines the Haber process to make ammonia. The reaction of nitrogen and hydrogen gases was first studied by Haber with Nemst and Bosch in the period 1904-1916. The two gases are adjusted to a 3 1 H2 N2 mixture and compressed to 2,000-10,000 psi (150-600 atm). The mixture is filtered to remove traces of oil, joined to recycled gases, and is fed to the reactor at 400-600°C. The reactor (Fig. 4.2) contains an iron oxide catalyst that reduces to a porous iron metal in the H2 N2 mixture. Ruthenium on... 

Ammonia is produced from nitrogen and hydrogen at elevated temperature (500 to 550°C) and pressure (200-350 atm) (Haber-Bosch process), using a promoted iron catalyst... 

Another important application of iron is as an industrial catalyst. It is used in catalyst compositions in the Haber process for synthesis of ammonia, and in Fischer-Tropsch process for producing synthetic gasoline. 

Nitrogen reacts with hydrogen at 400° C and 200 to 300 atm pressure in the presence of a catalyst, such as iron oxide, to form ammonia (the Haber process) ... 

The importance of catalysts in chemical reactions cannot be overestimated. In the destruction of ozone previously mentioned, chlorine serves as a catalyst. Because of its detrimental effect to the environment, CFCs and other chlorine compounds have been banned internationally. Nearly every industrial chemical process is associated with numerous catalysts. These catalysts make the reactions commercially feasible, and chemists are continually searching for new catalysts. Some examples of important catalysts include iron, potassium oxide, and aluminum oxide in the Haber process to manufacture ammonia platinum and rhodium in the Ostwald synthesis of nitric... 

An important aspect of the Haber process is the use of several catalysts in the reaction. A major problem in Haber s attempt to synthesis ammonia was identification of suitable catalysts. Haber discovered that iron oxides worked as the primary catalysts in combination with smaller amounts of oxides of potassium and aluminum. 

The Haber process is the reaction of nitrogen and hydrogen to produce ammonia. The two elements nitrogen and hydrogen are reacted over an iron catalyst under 200 atm, at 450 °C to produce ammonia. 

These relative chemisorption strengths enable us to make some simple predictions regarding suitable metal catalysts for specific reactions. For example, a catalyst for the Haber process must chemisorb both N2 and H2, but not too strongly. Since N2 is the less readily bound, we choose Fe, Ru, or Os. The latter two are expensive, so our best choice is iron—usually finely divided, on a suitable refractory support. 

In the Haber process, nitrogen and hydrogen in the correct proportions (1 3) are pressurised to approximately 200 atmospheres and passed over a catalyst of freshly produced, finely divided iron at a temperature of between 350 °C and 500 °C. The reaction in the Haber process is ... 

Table 5.1 shows an application of XPS to the study of the promoted iron catalyst used in the Haber synthesis of ammonia. The sizes of the various electron intensity peaks allows a modest level of quantitative analysis. This catalyst is prepared by sintering an iron oxide, such as magnetite (Fe304) with small amounts of potassium nitrate, calcium carbonate, aluminium oxide and other trace elements at about 1900 K. The unreduced solid produced on cooling is a mixture of oxides. On exposure to the nitrogen-hydrogen reactant gas mixture in the Haber process, the catalyst is converted to its operative, reduced form containing metallic iron. As shown in Table 5.1, the elemental components of the catalyst exhibit surface enrichment or depletion, and the extent of this differs between unreduced and reduced forms. 

The manner in which this equilibrium is influenced by changes in temperature and pressure should be reviewed. In practice, ammonia is produced by the Haber process at temperatures ranging from 400 to 600°C and at pressures between 200 and 1000 atm. Catalysts that are suitable for use in this process include a mixture of the oxides of iron, potassium, and aluminum iron oxide alone mixtures of iron and molybdenum the metals platinum, osmium, uranium and a number of others as well. 

The chemical unreactivity of the N=N bond is clearly seen when one considers the industrial process of nitrogen fixation. This process, devised by Fritz Haber in 1910 and still used today in fertilizer factories, involves the reduction of N2 in the presence of H2 gas over an iron catalyst at a temperature of 500°C and a pressure of 300 atmospheres. 

The first breakthrough in the large-scale synthesis of ammonia resulted from the development of the Haber process in 1913 in which ammonia was produced by the direct combination of two elements, nitrogen and hydrogen, in the presence of a catalyst (iron oxide with small quantities of cerium and chromium) at a relatively high temperature (550°C) and under a pressure of about 2940 psi (20.3 MPa). 

The iron catalyst used in the synthesis of ammonia (Haber s process) is poisoned by H2S. 

Ammonia is made by the Haber process using an iron catalyst. 

Fritz Haber developed the Haber Process for synthesizing ammonia from hydrogen and nitrogen using an iron catalyst. Ammonia is still produced by this method to make fertilizers, textiles, and other products. 

In most processes the reaction takes place on an iron catalyst. The reaction pressure is normally in the range of 150 to 250 bar, and temperatures are in the range of 350°C to 550°C. At the usual commercial converter operating conditions, the conversion achieved per pass is only 20% to 30%53. In most commercial ammonia plants, the Haber recycle loop process is still used to give substantially complete conversion of the synthesis gas. In the Haber process the ammonia is separated from the recycle gas by cooling and condensation. Next the unconverted synthesis gas is supplemented with fresh makeup gas, and returned as feed to the ammonia synthesis converter74. 

The promoted iron catalyst to accelerate this reaction was discovered by Bosch, Mittasch, and coworkers, in 1909. Consequently, the industrial process for the production of ammonia is named the Haber-Bosch process. In this process, ammonia is formed by the reaction between N2 and H2 using a Fe304 (magnetite) catalyst promoted with A1203, CaO, K20, and other oxides. 

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