Ammonia catalytic decomposition

Mardaleishvilli, Sin-Chou, and Smorodin-skaya [Kinetics and Catalysis, 8 (664), 1967] have studied the catalytic decomposition of ammonia on quartz. The following initial rate data were obtained by these investigators at 951 C... 

The following data give a short historic survey on the first steps toward a synthesis of ammonia from hydrogen and nitrogen. In 1823, Eobereiner claimed to have achieved an ammonia synthesis from the elements (20). His experiments proved to be erroneous. In 1884, Ramsay and Young (21) showed that the catalytic decomposition of ammonia does not proceed quantitatively, a first indication for the exist-... 

Spectroscopic Monitoring of the Heterogeneous Catalytic Decomposition of Gaseous Ammonia 256... 

Heterogeneous and catalytic reactions also give straight lines over as wide ranges of temperature as can be investigated. For example, in the catalytic decomposition of ammonia on the surface of a tungsten wire the value of A remains constant over the range 904° to 1,129° abs. in a manner which confirms the equation completely. 

In solutions this type of reaction is common with enzymes it is also frequently found in the catalytic hydrogenation of liquids. An example of a nearly zero-order gas reaction is to be found in the catalytic decomposition of ammonia on the surface of tungsten, and also on the surface of molybdenum, f Thus at 856° C., with 200 mm. of ammonia in contact with a heated tungsten wire, 59 mm. were decomposed in 500 seconds, while in 1,000 seconds 112 mm. were decomposed. The falling off from linearity is but slight. This is illustrated by the accompanying figure, where the thicker lines represent the theoretical curves for a reaction of zero-order. 

For particular purposes, hydrogen is produced by catalytic decomposition of ammonia (by contact with nickel at 900°C for hydrogenation or metallurgical purposes) or methanol in cracking plants. 

In general, the reaction order does not follow from the stoichiometry of the chemical equation. In the case of the catalytic decomposition of ammonia on a hot platinum wire, the reaction order is zero initially because the reaction occurs on the surface of the wire, and the surface coverage is independent of concentration. The rate of a zero-order reaction is independent of concentration until the reactant is nearly exhausted or until equilibrium is reached. 

Derivation (1) Reaction of steam with natural gas (steam reforming) and subsequent purification (2) partial oxidation of hydrocarbons to carbon monoxide and interaction of carbon monoxide and steam (3) gasification of coal (see Note 1) (4) dissociation of ammonia (5) thermal or catalytic decomposition of hydrocarbon gases (6) catalytic reforming of naphtha (7) reaction of iron and steam (8) catalytic reaction of methanol and steam (9) electrolysis of water (see Note 2). In view of the importance of hydrogen as a major energy source of the future, development of the most promising of these methods may be expected. 

The determination of ammonia content in gas samples by vapor phase chromatographic analysis for nitrogen after catalytic decomposition was described by Diedrich et al. A Dynatronics chrom-Analyzer model 100 gas chromatograph equipped with thermal conductivity detector was... 

Diedrich, A. T., Bult, R. P., and Ramaredhya, J. M., Determination of ammonia in gas samples by vapour phase chromatographic anlaysis for nitrogen after catalytic decomposition, J. Gas... 

There is an important number of commercial approaches to NO removal, including adsorptive, thermal and catalytic techniques (Armor 1994, Centi and Forzatti 1995, Fritz and Pitchon 1997). In the case of catalytic processes, the elimination of NO can be carried out by direct catalytic decomposition, or by selective catalytic reduction (SCR) using hydrocarbons or ammonia as reductant. Although several catalytic system have been studied, zeolites have been proposed as interesting catalysts for both reactions. 

The pore size of large-pore zeolite HB is controlled by an improved chemical vapor deposition (CVD). In this method, ammonia or tripropylamine was used to protect the acidic sites in zeolite before deposition of (CH3)3Si-0-Si(CH3)3, differently from the conventional CVD. The pore volume of zeolite HB was reduced and the pore size was narrowed upon this modification. The results from IR spectra and catalytic decomposition of isopropanol demonstrated that the modified samples showed stronger acidity than that prepared from conventional CVD. In the transformation of trimethylbenzenes (TMB), conversion of 1,3,5-TMB was suppressed while conversion of 1,2,3-TMB was almost unaffected on the improved CVD samples the selectivity of 1,2,4-TMB on these samples was increased in the alkylation reaction of m-xylene with methanol. 

Experiment 19.4 Catalytic decomposition of urea by the enzyme urease Some phenolphthalein solution is added to solutions of urea and methylurea which are then divided into three goblets (see illustration). The urea solution in the first glass serves as the reference. A suspension of urease is added to the second goblet containing urea solution as well as to the third containing methylurea solution. After a short while, the urea solution has a violet color due to formation of ammonia, while the methylurea solution remains unchanged. 

Ammonia is a potential hydrogen carrier (17.6 wt%) and is a liquid at room temperature around 6 atm pressure. " As a fuel it will not generate CO, CO2 or C in combination with hydrogen, which is advantageous. Ammonia converts (> 99%) to nitrogen and hydrogen in a weakly endothermic reaction via catalytic decomposition, as in eqn (11.11) ... 

Kinetic catalytic methods based on catalytic decomposition, hydrolysis, ligand-exchange, or complex-formation reactions have a promising future as they allow the determination of nontransition metals such as alkaline earths (whether individually or in mixtures), in addition to ammonia and some other species. 

Ampere assumed an intermediate formation of nitride in the catalytic decomposition of ammonia gas by heated metals. W. C. Henryk criticised Faraday s condensation theory. On the basis of experiments he concluded that ... 

Several techniques have been considered to decrease NOx emission, such as selective noncatalytic reduction (SNCR), selective catalytic reduction (SCR) with ammonia (NH3) or hydrocarbon, and direct catalytic decomposition of NO. The main disadvantage of the SCR process is the high cost associated with the consumption of reductants. Nevertheless, direct catalytic decomposition of NO without the addition of reducing agents is an effective and economical procedure to decrease NOx emission. Therefore, the direct decomposition of NO into N2 and O2 (2NO = N2 + O2) is the optimal way for NO removal, because the process is simple and there is no necessity for a reductant such as a hydrocarbon, NH3, or urea. 

Further work by Spetz et al (21) showed that the thick contact electrode did not have to be made from palladium. Their initial theory of operation was therefore modified to postulate that the hydrogen atoms, generated from the catalytic decomposition of the ammonia, caused an interfacial dipole layer to be formed at the platinum (or iridium)/silicon dioxide interface, not at the palladium/silicon dioxide interface. 

Zheng W, Zhang J, Zhu B, Blume R, Zhang Y, Schlichte K, Schloegl R, Schueth F, Su DS. Structure-function correlations for Ru/CNT in the catalytic decomposition of ammonia. Chem Sus Chem 2010 3 226-30. 

The catalytic decomposition of ammonia, preferably performed at around 600 °C, is another interesting alternative to fuel processing based upon fossil fuels [34] ... 

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