Catalysts ammonia synthesis

Shift Conversion. Carbon oxides deactivate the ammonia synthesis catalyst and must be removed prior to the synthesis loop. The exothermic water-gas shift reaction (eq. 23) provides a convenient mechanism to maximize hydrogen production while converting CO to the more easily removable CO2. A two-stage adiabatic reactor sequence is normally employed to maximize this conversion. The bulk of the CO is shifted to CO2 in a high... 

Final Purification. Oxygen containing compounds (CO, CO2, H2O) poison the ammonia synthesis catalyst and must be effectively removed or converted to inert species before entering the synthesis loop. Additionally, the presence of carbon dioxide in the synthesis gas can lead to the formation of ammonium carbamate, which can cause fouHng and stress-corrosion cracking in the compressor. Most plants use methanation to convert carbon oxides to methane. Cryogenic processes that are suitable for purification of synthesis gas have also been developed. 

Promoters. Many industrial catalysts contain promoters, commonly chemical promoters. A chemical promoter is used in a small amount and influences the surface chemistry. Alkali metals are often used as chemical promoters, for example, in ammonia synthesis catalysts, ethylene oxide catalysts, and Fischer-Tropsch catalysts (55). They may be used in as Httie as parts per million quantities. The mechanisms of their action are usually not well understood. In contrast, seldom-used textural promoters, also called stmctural promoters, are used in massive amounts and affect the physical properties of the catalyst. These are used in ammonia synthesis catalysts. 

Ammonia production from natural gas includes the following processes desulfurization of the feedstock primary and secondary reforming carbon monoxide shift conversion and removal of carbon dioxide, which can be used for urea manufacture methanation and ammonia synthesis. Catalysts used in the process may include cobalt, molybdenum, nickel, iron oxide/chromium oxide, copper oxide/zinc oxide, and iron. 

Ammonia Synthesis Catalyst under Working Conditions... 

What is the rate-determining step of the ammonia synthesis reaction Describe the function of promoters in the ammonia synthesis catalyst. 

Explain why it is important to develop an ammonia synthesis catalyst with high activity at low temperatures. 

Jacobsen CJH, Dahl S, Clausen BS, Bahn S, Logadottir A, Nprskov JK. 2001. Catalyst design by interpolation in the periodic table bimetallic ammonia synthesis catalysts. J Am Chem Soc 123 8404-8405. 

LEIS has been applied to study the surface composition of Co-Mo and Ni-Mo hydrodesulfurization catalysts [46-48], Fe-based Fischer-Tropsch [49] and ammonia synthesis catalysts [50], and model systems such as Pt evaporated on Ti02 [51]. The review of Horrell and Cocke [52] describes several applications. 

In comparison to most other methods in surface science, STM offers two important advantages STM gives local information on the atomic scale and it can do so in situ [51]. As STM works best on flat surfaces, applications of the technique in catalysis concern models for catalysts, with the emphasis on metal single crystals. A review by Besenbacher gives an excellent overview of the possibilities [52], Nevertheless, a few investigations on real catalysts have been reported also, for example on the iron ammonia synthesis catalyst, on which... 

N2 and CO, respectively [31,32], Empirical knowledge about the promoting effect of many elements has been available since the development of the iron ammonia synthesis catalyst, for which some 8000 different catalyst formulations were tested. Recent research in surface science and theoretical chemistry has led to a fairly complete understanding of how a promoter works [33,34],... 

Since theoretical calculation of effectiveness is uncertain and is moreover sensitive to operating conditions, for industrially important cases it is determined by such reaction tests. Common types of curve fits may be used. For ammonia synthesis catalyst, for instance, an equation is provided by Dyson Simon (IEC Fundam 7 605, 1968) in terms of temperature and... 

Bridger, G.W. Snowden, C.B. (1970) Ammonia synthesis catalysts. In Catalyst Handbook. Wolfe Scientific Books, 126-147 Brindley, G.W. Bish, D.L. (1976) Green rust a pyroaurite type structure. Nature 263 353 Bromfield, S.M. Williams, E.G. (1963) An examination of the biological reduction method for estimating active iron in soils. J. Soil Sd. 14 346-359... 

Ammonia, Hydrogen, and Methanol Production The ammonia synthesis catalyst is metallic iron promoted with AljO,. K 0. MgO. and CaO. The hydrogen-producing (methane reforming) catalyst is supported nickel. The methanol synthesis catalyst is ZnO promoted with Cr Oj or Cu(l>—ZnO promoted with CrjOl or AUOi. The respective reactions are cited as follows. 

The concepts underlying the derivation of (305) were also confirmed in the extensive study by Scholten (97). This author used a balance of special design that permitted following the weight changes of the ammonia synthesis catalyst in the course of the reaction and in the process of nitrogen adsorp-... 

Equation (341) solves the task of quantitatively describing the effect of water vapor, and also oxygen gas (the last being rapidly converted to water vapor at the conditions of the reaction), on the activity of commercial ammonia synthesis catalysts. This result is of practical importance for ascertaining the necessary degree of purity of the inlet gas mixture with respect to poisons containing oxygen (122). 

In contrast to poisoning with water vapor, the poisoning of ammonia synthesis catalysts by hydrogen sulfide is irreversible. It was studied using H2S labeled with H 5S (123) that made the radiochemical technique applicable to the determination of sulfur content in catalysts. 

Apparent Activation Energy of Ammonia Synthesis Catalysts for Formic Acid... 

Anon( Ref 67) and Reidel (Ref 79) describe the Phillips Chemical Co plant near Houston, Texas. It is the NEC (Nitrogen Engineering Corp) medium pressure process utilizing natural gas as starting material. Resen(Ref 70) describes the manuf of ammonia at the Lion Oil Co plant in Louisiana. Frankenburg (Ref 51) studied the relationship between the nature and the effectiveness of ammonia synthesis catalysts. Other studies of synthesis catalysts were made by Odelh6g(Ref 44), Enomoto Horiuchi(Refs 53 54), Nielsen(Ref 60), Emmett(Ref 74) and Faith... 

Fastrup, B. (1994) Temperature programmed adsorption and desorption of nitrogen on iron ammonia synthesis catalysts, and consequences for the microkinetic analysis of NH3 synthesis. Top. Catal., 1, 273. 

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