Energy for ammonia synthesis

Figure 7.26. The activation energy for ammonia synthesis on Fe(lll) and K/Fe(lll). Within experimental error there is no change, suggesting that potassium does not change the reaction mechanism of ammonia synthesis [59].

Table 10.8 Comparison of theoreticeJ consumption of energy for ammonia synthesis using different materials/(GJ/tNHa)...

Finally, the overall activation energy for ammonia synthesis predicted by this potential energy diagram is 17kJmor which is considerably lower than the experimental values of 45 kJ mol of Nielsen or the 81 kJ mol" of Somorjai et... 

Addition of too much K increases the activation energy for ammonia synthesis [176, 242]. The optimum concentration of K [67, 68] depends on the nature and concentration of the structural promoters [291], and on the preparation method [612]. 

Table 6.1 Standard free energy of formation data for ammonia synthesis.

Fig. 4.2 Mechanism and energy diagram for ammonia synthesis on iron. (Energies in l

Due to the high hydrogen storage capacity of the ammonia molecule (17.7 wt% equal to an energy density of 4,318 Wh kg 1), its decomposition is intensely investigated for COx-free hydrogen production for mobile fuel cell applications [146]. However, compared with the well-established Haber Bosch process for ammonia synthesis, its decomposition is underdeveloped and requires substantial improvements before it can be considered as a practical contribution to the energy supply toolbox. 

Figure 4.15. Calculated potential energy diagram for ammonia synthesis over a close-packed and a...

Calculate the free-energy change for ammonia synthesis at 25°C (298 K) given the following sets of partial pressures ... 

It should be noted that the results for the formic acid decomposition donor reaction have no bearing for ammonia synthesis. On the contrary, if that synthesis is indeed governed by nitrogen chemisorption forming a nitride anion, it should behave like an acceptor reaction. Consistent with this view, the apparent activation energy is increased from 10 kcal/mole for the simply promoted catalyst (iron on alumina) to 13-15 kcal/mole by addition of K20. Despite the fact that it retards the reaction, potassium is added to stabilize industrial synthesis catalysts. It has been shown that potassium addition stabilizes the disorder equilibrium of alumina and thus retards its self-diffusion. This, in turn, increases the resistance of the iron/alumina catalyst system to sintering and loss of active surface during use. 

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

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