Ammonia on ruthenium

SSIMS has also been used to study the adsorption of propene on ruthenium [3.29], the decomposition of ammonia on silicon [3.30], and the decomposition of methane thiol on nickel [3.31]. 

H. Jobic, M. Lacroix, T. Decamp M. Breysse (1995). J. Catal., 157, 414—422. Characterization of ammonia adsorption on ruthenium sulfide. Identification of amino species by inelastic neutron scattering. 

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). 

The only synthetic report on ruthenium(ii)-dinitrogen complexes is a new route to the complex [Ru(NH3)4(N2)(H20)]l2, via the action of nitric acid and excess hydrazine hydrate on K2[Ru(NO)Cl . The red compound is stable for at least six months in air, but decomposes slowly in water, ammonia, or alkaline solution. 

S.R. Deshmukh, A.B. Mhadeshwar, D.G. Vlachos, Microreactor modeling for hydrogen production from ammonia decomposition on ruthenium, Ind. Eng. 

In some cases the so-called "Steady-State Isotopic Transient Kinetic Analysis" (SSITKA) was used for detailed investigations of reaction mechanisms. Shannon and Goodman [123] present an extensive review of this subject. Hinrichsen et al. [124] employed temperature programmed desorption to study the ammonia synthesis on ruthenium catalysts. 

Probably the most comprehensive published assay of DU used in armor pen-etrators was reported on the basis of analysis of an unfired CHARM-3 penetrator (Trueman et al. 2004). A sample from the penetrator was dissolved in 9 M HCl, spiked with U as a yield monitor, and the uranium was separated from impurities on an ion-exchange resin. The isotopic composition of uranium was determined by mass spectrometric techniques. Actinides ( - Am and Np) were determined in the uranium-free solution by gamma spectrometry and 239+24opy and Pu were measured by alpha spectrometry and their presence was confirmed by ICPMS. Technetium-99 was determined by ICPMS when rhenium was used as a carrier and interferences from iron were eliminated by precipitating with ammonia while ruthenium and molybdenum were removed by separation on a chromatographic resin. The content of these radioactive nuclides is summarized in Table 2.7. 

As early as the middle of 1960s, BP successfully developed a kind of oleophylic graphite with excellent adsorption ability, and then a kind of graphited carbon in 1974, which could be used as supports for various catalysts. From 1978 to 1984, BP claimed a series of patents on ruthenium catalysts for ammonia synthesis. In 1979, ° a novel catalyst for ammonia synthesis was prepared by loading carbonyl compound of ruthenium on carbon containing graphite in laboratory. This kind of catalyst, with graphited carbon as support and Rus (CO) 12 as the precursor, possessed some special features that may be summarized as follows ... 

Like iron catalyst, dissociative adsorption of N2 is also the rate determining step on ruthenium catalyst. The difference is that the absorption of H2 strongly inhibits the adsorption of N2, while the inhibition effect for the production of NH3 is not apparent on ruthenium catalyst.The latter is an advantage of ruthenium catalyst, so that the ruthenium catalyst can be placed behind iron catalyst in synthesis ammonia process, e.g., KAAP process.The former effect is still a problem that needs to be solved for the ruthenium catalysts. 

In 1990, the Pacific ammonia synthesis project was initiated. At the same year, Engelhard Corporation obtained the production license of the catalyst. In 1991, Kellogg obtained the catalyst technology from BP Company. In November 1992, Kellogg announced that the first KAAP started up successfully based on ruthenium ammonia s mthesis catalysts at Pacific Ammonia. 

There is no consistent understanding on the role of mechanism of alkali metals and alkaline earth metals on ruthenium catalysts and their state under the operating conditions. The current studies show that the dynamics of the ammonia synthesis reaction are different using the alkali metals and alkaline earth metals as the promoters, respectively. Therefore, using combination of promoters is more favorable to increase the catalytic activity. 

According to the promotion role of K on ammonia synthesis and nitrogen isotopic equilibrium over Ru/AC and pure ruthenium catalysts, it is found that with adding K at 673 K, the activity increases by 500 times on ruthenium catalyst, while the activity only increases by 25 times on Fe catalyst due to the inhibition of hydrogen. The inhibition of hydrogen is caused by the competitive adsorption of hydrogen which can inhibit the adsorption of nitrogen. ... 

It is seen that because there are the competitive adsorption of H2 and N2 on the surface of ruthenium catalyst and the adsorption heat of H2 is larger than N2, so the strong adsorption of H2 occupies the active site of the catalyst surface, and is likely to generate hydrogen bridged compounds of sub-layer, especially on the system in which alkali metal hydroxide is used as promoter. Many of the activity sites on ruthenium catalyst are firmly occupied by H2, which hindered the determining reaction step of N2 dissociative adsorption and the reaction rate of ammonia formation is decreased. 

Table 6.47 Hydrogen effect on ruthenium-beised ammonia synthesis catalyst...

It can be seen from these figures that the change of activity of A301 iron catalyst is very little with H2/N2 ratio, while it is obvious on Ru catalyst. At 400°C, the activity of Ru catalyst increases with the decreasing of H2/N2 ratio when it is higher than 1.5 and decrease when H2/N2 ratio is lower than 1.5 (Fig. 6.66). Here, the activity is above 22% on ruthenium catalyst and the equilibrium ammonia concentration is about 25% at H2/N2 = 3. At the same time, equilibrium ammonia concentration also decreases with the decrease of H2/N2 ratio. Therefore, the effect of change of H2/N2 ratio is not too obvious. For iron catalysts, the activity does not change with the decrease of H2/N2 ratio until H2/N2 ratio is lower than 0.67 at 400°C. 

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