Ammonia synthesis properties

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. 

Calcium cyanamid process, for ammonia synthesis, 11 114, 115 Calcium cyanide, 8 194-197 Calcium cyanide diammoniate, 8 195 Calcium dichromate, molecular formula, properties, and uses, 6 561t 5-Calcium disilicate monosulfate, phase in Portland cement clinker, 5 472t 5-Calcium disilicate monocarbonate, phase in Portland cement clinker, 5 472t Calcium disilicide, 4 530 8-Calcium disodium trialuminate, phase in Portland cement clinker, 5 472t Calcium doping, 23 842-844 Calcium P-alumina, 2 406t Calcium ethylenediaminetetraacetate, 7 596t... 

The present paper focuses on the interactions between iron and titania for samples prepared via the thermal decomposition of iron pentacarbonyl. (The results of ammonia synthesis studies over these samples have been reported elsewhere (4).) Since it has been reported that standard impregnation techniques cannot be used to prepare highly dispersed iron on titania (4), the use of iron carbonyl decomposition provides a potentially important catalyst preparation route. Studies of the decomposition process as a function of temperature are pertinent to the genesis of such Fe/Ti02 catalysts. For example, these studies are necessary to determine the state and dispersion of iron after the various activation or pretreatment steps. Moreover, such studies are required to understand the catalytic and adsorptive properties of these materials after partial decomposition, complete decarbonylation or hydrogen reduction. In short, Mossbauer spectroscopy was used in this study to monitor the state of iron in catalysts prepared by the decomposition of iron carbonyl. Complementary information about the amount of carbon monoxide associated with iron was provided by volumetric measurements. 

None of the above properties and characteristics act independently. When one among them is changed with a view to improvement, the others are also modified and not necessarily in the direction of an overall improvement. As a result, industrial catalysts are never ideal. Fortunately, however, the ideal is not altogether indispensable. Certain properties, such as activity and reproducibility, are always necessary, but selectivity, for example, has hardly any meaning in reactions such as ammonia synthesis, and the same holds true for thermal conductivity in an isothermal reaction. Stability is always of interest but becomes less important in processes that include continuous catalyst regeneration. Regenerability must be optimized in this case. 

An important property of the multicomponent catalysts was that with highly purified gases, they remained active over long periods, a fact which greatly helped their practical usage for the technical ammonia synthesis. 

Another important factor in the catalytic properties of Fe and other metallic catalysts is the structure of these catalysts. It is a well-known fact that during ammonia synthesis, when it is exposed on the surface of a Fe catalyst s (111) plane, the catalyst is more active [14],... 

As will be discussed later, we can conclude from other evidence that the surface of a catalyst for ammonia synthesis is actually heterogeneous in respect to catalytic activity and that, in all probability differences in the amount and nature of the promoters cause variations of electronic properties, observable by changes of the work function and of the catalytic activity. This conclusion may be expressed by stating that the activity change caused by promoters cannot be considered solely as a local action a point which has been especially well clarified by recent work on catalysts which are semiconductors. 

The hydrido dinitrogen complexes, whilst failing to fulfill the modern alchemists dream of a catalyst for the low temperature low pressure ammonia synthesis, have been thoroughly investigated and some of their spectroscopic properties are listed in Table 10. 

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