Ammonia adsorption equilibrium

Cu(NH3)2BTC2/3 and finally copper hydroxide in the presence of water. The formation of the BTC salts was supported by the collapse of the structure after interaction of ammonia with unsaturated copper centers. The release of BTC and copper oxide centers provides sites for reactive adsorption of ammonia during the course of the breakthrough experiments. Interestingly, even though the structure collapses, some evidence of the structural breathing of the resulting materials caused by reactions with ammonia was found, based on the ammonia adsorption at equilibrium and the analysis of the heat of interactions [51]. 

Katada, N., Igi, H., Kim, J.H., and Niwa, M. (1997) Determination of the acidic properties of zeolite by theorecti-cal analysis of temperature programmed desorption of ammonia based on adsorption equilibrium. J. Phys. Chem. B, 101, 5969-5977. 

A two-site model was used as well by Shih et al. (102) for the HDN of quinoline. They assumed not only pseudo-first-order kinetics but also that all nitrogen-containing species, including ammonia, have the same adsorption equilibrium constant this is clearly not the case (77). 

By hypothesizing that ammonia and water compete for adsorption onto the active sites and that adsorption equilibrium is established for both species, the following relations hold ... 

Sousa Neto VO, Carvalho TV, Honorato SB, Gomes CL, Barros FCF, Araujo-Silva MA, Freire PTC, Nascimento RF. Coconut bagasse treated by thiourea/ammonia solution for cadmium removal kinetics and adsorption equilibrium. BioResources 2012 7 1504-1524. 

A calorimetric study of ammonia adsorption on zeolites has confirmed that, at 303 K, the adsorption process involves a slow redistribution of adsorbed species, so that a longer time is needed to achieve thermal equilibrium [30]. The rate of heat liberation depends strongly on the amount of ammonia adsorbed. At higher temperature this phenomenon cannot be observed. The data related to the thermokinetic behavior of ammonia adsorbed on faujasite, L and mordenite type zeolites are discussed [30]. The position of the maximum on the kinetic cmves depends on the chemical composition of the zeolite and on the degree of filling of the cavities of the zeolite by the molecules adsorbed. The slow liberation of the heat is associated with a redistribution of the adsorbed molecules. 

Based on the principle of equilibrium state approximation, only one elementary step is the determining step for the three kinetic models listed in Table 2.5. The overall rate of a reaction is determined by the rate of the rate determining step (RDS) with slowest rate, while other steps are approximately in chemical or adsorption equilibrium. There are three opinions or possibilities for the rate determining step of ammonia synthesis reaction on fused iron catalyst (i) RDS is the dissociation of adsorbed dinitrogen N2(ad) 2N (ad) (ii) the surface reaction of adsorbed species N (ad) + H (ad) NH (ad) (iii) the desorption of adsorbed ammonia NH3(ad) NHs(g). 

This mechanism can be converted to a kinetic scheme to describe the steady state or transient performances of the catalyst. Assuming (i) an Eley-Rideal mechanism (reaction between adsorbed NH3 and gas-phase NO), (ii) that ammonia and water compete for adsorption onto the active sites, and (iii) that adsorption equilibrium is established for both species, the following Rideal rate expression is eventually obtained [6] ... 

Figure 17.4. Equilibrium data for the adsorption of ammonia on charcoal1 10) (a) Adsorption isotherm (b) Adsorption isobar (c) Adsorption isostere...

The character of the chemisorption of nitrogen can be also judged from the results of studies of ammonia synthesis kinetics at the reversible poisoning of the catalyst with water vapor (102,103). If a gas mixture contains water vapor, an adsorption-chemical equilibrium of adsorbed oxygen, hydrogen gas, and water vapor sets in on the iron catalyst. 

We have found that the waste wood and used tealeaves showed high adsorption capabilities for ammonia gas in low equilibrium pressure (< 13.3 kPa). The amount of the adsorbed ammonia for these carbonized materials were much higher that of the activated carbon Granular Shirasagi GS3 x 4/6. These results suggest that the carbonized materials from organic wastes could be utilized as adsorbents for ammonia... 

Adsorption capacities of the carbonized materials for ammonia gas were analyzed by batch-wise equilibrium experiment using a micro-balance. The experimental methods were described in the previous paper in detail [6]. 

In applying these equations, the authors assumed that the adsorption of nitrogen on the iron catalyst in the presence of an ammonia-hydrogen mixture is the same as it would be when at a nitrogen pressure equivalent to the existing partial pressure of ammonia and hydrogen in the gas mixture. Thus, since the equilibrium constant for ammonia synthesis is... 

In our group a comparison has been made between the adsorption of some gases (carbon dioxide, ammonia, ethane and ethylene) and water (measured in equilibrium with the vapour pressure at 93.1 kPa and 25°C) for the aluminosilicate Na-A [37,38] and the all- ca DD3R. 

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