Nitrogen adsorption reaction pathway

Numerous quantum mechanic calculations have been carried out to better understand the bonding of nitrogen oxide on transition metal surfaces. For instance, the group of Sautet et al have reported a comparative density-functional theory (DFT) study of the chemisorption and dissociation of NO molecules on the close-packed (111), the more open (100), and the stepped (511) surfaces of palladium and rhodium to estimate both energetics and kinetics of the reaction pathways [75], The structure sensitivity of the adsorption was found to correlate well with catalytic activity, as estimated from the calculated dissociation rate constants at 300 K. The latter were found to agree with numerous experimental observations, with (111) facets rather inactive towards NO dissociation and stepped surfaces far more active, and to follow the sequence Rh(100) > terraces in Rh(511) > steps in Rh(511) > steps in Pd(511) > Rh(lll) > Pd(100) > terraces in Pd (511) > Pd (111). The effect of the steps on activity was found to be clearly favorable on the Pd(511) surface but unfavorable on the Rh(511) surface, perhaps explaining the difference in activity between the two metals. The influence of... 

It is clear from the results reported in Table 1 that the side-on adsorption on Ru(l 10) is actually higher in energy than the end-on configuration. Tomanek and Bennemann [29] obtained similar results from a theoretical study of nitrogen adsorption on Fe( 111). This weaker adsorption is consistent with the simultaneous lengthening of the N-N and N-Ru bonds as the end-on configuration falls over to the side-on state. Therefore, as discussed in the previous section, the main role of the side-on state is not as a stable surface intermediate at reaction temperatures, since even the end-on is more stable, but rather as a pathway from the end-on to the dissociated state. 

The NSR mechanism especially over Ba-containing systems has been elaborated over the first years of their application and can be simunarized in seven steps, whereas intermediate species and reaction pathways are still open issues [63]. Under lean conditions, the NSR promotes NO adsorption as illustrated by reactions (26.7) and (26.8), where E is the NO adsorbing element EO is the CO2 adsorber material (Eq. (26.11)), and ENO3 is the stable solid compound formed after NO adsorption under 2 > 1 (Eq. (26.8)). Dimng the short fuel-rich conditions, when some reductant (e.g., H2 or HC) is injected, stored NO -adsorbed species are released (Eq. (26.9)). Subsequently, catalytic reduction of the formed gaseous NO to nitrogen gas occurs over Pt or Rh (Eq. (26.10)). 

The removal of the nitrogen atom from o-toluidine proceeds via two reactions by direct C-N bond cleavage of toluidine to toluene and ammonia (path 1), and by hydrogenation of o-toluidine to methylcyclohexylamine (path 2), which reacts further to methylcyclohexene, methylcyclohexane and ammonia [2]. Fig. 2 shows the influence of the initial partial pressure of o-toluidine on the selectivity for the products of these two pathways. Varying the initial partial pressure of o-toluidine in the reactant mixture did not affect the product selectivity. This indicates that either both reactions occur on the same site with the same order of reaction, or that o-toluidine has the same adsorption constant on the sites for path 1 and path 2. 

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