Dinitrogen dissociative adsorption

It should be emphasized that since the rate of ammonia synthesis on iron depends critically on the dissociative adsorption of dinitrogen (steps 1 and 2), any... 

Ruthenium has long been known to be an effective catalyst for ammonia synthesis. However, compared to the traditional iron-based catalysts, studies on ruthenium-based catalysts are limited. The rate determining step of ammonia synthesis, the dissociative adsorption of dinitrogen, has been shown to extremely structure sensitive on both iron and mthenium catalysts. To study this structure sensitivity on ruthenium, density functional theory calculations were performed on Ru(OOl) and Ru(llO) clusters. End-on, side-on, and dissociated adsorption states were investigated on both surfaces. While the Ru(llO) cluster could stabilize aJl three adsorption modes, a minimum energy structure for the side-on adsorption on Ru(OOl) could not be found. It is likely that this side-on mode can provide a low energy pathway to the dissociated state, thereby resulting in faster dissociative adsorption on Ru(llO). 

Dissociated adsorption of dinitrogen is the rds that produces the Mari N. Because of this assumption, all the other equilibrated steps may be summed up into an overall equilibrated reaction. So, the two-step sequences are ... 

In ammonia synthesis reaction, the dissociative adsorption of dinitrogen is the rate determining step. The electron donor type promoter, such as alkali metals, which can provide electrons to the Ru, is more propitious to activate the N=N bond in N2 molecule and thus enhance the dissociative adsorption of dinitrogen and increase the reaction rate of ammonia synthesis. The acidity and basicity of supports have important influence on the activity of the ruthenium catalysts without promoter. Acidic supports can easily accept electrons and decrease the activity of catalysts. Basic supports can easily provide electrons and enhance the dissociative... 

The dissociation adsorption rate (ra) and the desorption rate (rd) of dinitrogen molecule are,... 

Dissociative adsorption of dinitrogen molecule (N2 + 2 —> 2N ) is generally regarded as the rate determining step of ammonia sjmthesis reaction. The isotopic equilibration of nitrogen also needs dissociation of dinitrogen molecule ... 

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). 

It would be very difficult to discriminate between Eqs. (2.112) and (2.111) on the basis of fitting degree of kinetic data. To decide whether the adsorption of dinitrogen is dissociated or not, other experiments are needed. 

---