Adsorption energy of ammonia

This kinetic behavior indicates a rate-determining surface reaction of weakly adsorbed nitrous oxide on a surface which adsorbs ammonia according to Langmuir s isotherm. The adsorption energy of ammonia on the active surface was found to be 2.2 kcal./mol. 

In the ammonia oxidation system shown in Fig. 18, ammonia is adsorbed in the presence of oxygen on Cu(l 11). At lower surface coverages, atomic oxygen increases the adsorption energy of ammonia by 30 kJ/mol. The adsorption energy for ammonia in the presence of oxygen is -48... 

Figure 7.23. Ammonia TPD from clean Fe(lll) and K/Fe(lll) surfaces. The desorption temperature of ammonia from Fe(111) is lowered in the presence of potassium. Thus potassium lowers the adsorption energy of ammonia on the iron surface [59].

The adsorption energy of ammonia is dependent on the crystallographic orientation of the surface, as well as on coverage, and is typically of the order of about 70 kJ As a consequence, rapid desorption will take place at the... 

To describe catalytic reactions on a metal surface, adsorption energies of the reactants, intermediates and products are essential and so are the activation energies separating different intermediate steps. Figure 4.15 illustrates a full potential energy diagram for a catalytic reaction the synthesis of ammonia N2+3H2 — 2NH3. 

A common experimental means of characterizing the acidity of zeolites is the use of probe molecules. IR spectra leave no doubt that ammonium ions are formed upon adsorption of ammonia in zeolites, the OH band characteristic for bridging Si-0(H)-Al sites disappears and NH4+ bending bands appear [12]. The energy of ammonia desorption. 

Tab. 22.2 Proton transfer energy, A pj, deprotonation energy, E yp, hypothetical binding energy of NH4 on the deprotonated zeolite surfaces, E p(SH ), and energy of ammonia adsorption, ad( 3) ( J for Bronsted sites in different zeolite frameworks [13].

A comparison of the adsorption energies of the complexes formed by ammonia, pyridine and isopropylamine with a simple potential-energy model, which assumes that the heat of adsorption scales linearly with gas-phase proton affinities, suggests that proton transfer dominates the interaction between the adsorbate and the acid site [56],... 

The heats of adsorption of ammonia at 303 K on Linde molecular sieve X (Na-X and Ca-X) were also measured by Stone et al. [133]. Ca-X displayed higher heats of ammonia adsorption than the corresponding sodiiun zeolite at all coverages, the latter being represented by a homogeneous site population with an adsorption energy of around 47 kj mol ... 

Based on the research results of monometallic catalysts, scientists also studied on bimetallic catalysts for N2 activation. They realized that the adsorption energy of N2 determines the catalysts properties. Under specific reaction conditions, it can estimate adsorption energy of N2 on catalyst. The catalytic efficiency of the elements for the synthesis and decomposition of ammonia was correlated with the chemisorption energy of nitrogen. An inverted parabolic function (volcano curve) was obtained by Ozaki et in which iron, ruthenium, and osmium mark the top of the volcano. 

We conclude that anhydrous potassium hydroxide is the active species responsible for promotion by potassium and that the beneficial effect on ammonia synthesis is bifunctional, enhancing on the one hand the adsorption energy of molecular nitrogen, and reducing the adsorption energy of the product ammonia on the other. 

TABLE 5.4. Energetics of the Elementary Reactions of a High-Coverage, Activated Nitrogen Adsorption Model of Ammonia Synthesis Used to Construct the Potential Energy Diagram of Fig. 5.12... 

This can be done for all partial reactions and the onset potential as a function of the adsorption energy of N for the limiting reactions step as seen in Figure 18.11. On transition metal nano-clusters of selected catalyst, it is in principle possible to produce ammonia electro-chemically at an overpotential of —0.5 V, see Ref. [113] for details. A search for new catalysts using this surface termination is only necessary to calculate the adsorption energies of N and search for pure metals, nano-clusters alloys, or possibly nitrides which bind N by -1.1 eV. 

H2S is very poisonous for NH3 synthesis [14, 18, 721, 722] and N2 adsorption [513]. The poisoning is irreversible [14, 590]. The poisonous effect is due to S surface blockage [590, 723]. The activation energy of ammonia synthesis is unchanged during H2S poisoning [723] After exposure to large partial pressures of H2S, FeS may be observed by X-ray powder diffraction [590]. 

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