The activity of ruthenium catalyst

High activity is the most significant feature of ruthenium catalyst. The ammonia concentration or ammonia net value in outlet of converter can be significantly increased in industry. 

In order to investigate the catalytic activity of Ru catalysts, and compare with iron catalyst, we choose the representative iron catalyst A301 with wiistite as precursor as the reference sample. A301 has the highest activity among all of the iron-based catalysts for ammonia synthesis and now it has been widely used in ammonia synthesis industry. In order to get the reliable and comparable data of the evaluation of catalytic activity, the experiment was conducted under the same conditions and four samples were filled in four reactor contained in one shell. The results were shown in Table 6.41 and Figs. 6.56-6.58. 

Compared with Ba-Ru-K/AC catalyst, the inhibition of H2 adsorption on the iron catalyst is weaker. Therefore, the activity of iron catalyst does not decrease sharply as Ba-Ru-K/AC catalyst at low temperatures. 

Due to the high activity (ammonia neat value) used at above 15 MPa and the heat transfer problem of converter needs to be solved. One of the ways is to use multibeds, intercooled, radial-flow ammonia converter and to use ruthenium catalyst combined with iron catalyst. If the ruthenium catalyst was put after iron catalyst in converter, it can not only solve the heat transfer problem, but also reduce the quantity of the ruthenium catalyst. Therefore, the ruthenium catalyst can be applied in the present ammonia synthesis process. After further renovation of the process, the effect of save energy can be obtained. 

R is reported that KAAP-type Ru catalyst supported on graphitized carbon developed by BP is the best reported ruthenium catalyst. With the combination of this catalyst and iron catalyst, the designed outlet ammonia concentration is 20% and the actual concentration is 21.17% at 8.96MPa (91.4kgf/cm ). 

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Although the activities of ruthenium catalysts are much lower than that of chloroplatinic acid in the hydrosilylation of alkenes, RuCl2(PPh3)3 turned out to be an excellent... 

TOF of ammonia synthesis reaction and isotopic equilibrium rate of nitrogen molecule follow the order shown in Table 6.8. We can roughly estimate the performance of promoters from chemical property of element itself. The activity of ruthenium catalysts supported on AI2O3 is very low, while almost no activity is observed on activated carbon due to the acidicity of AI2O3 and absorption of electrons by activated carbon. 

At 350°C (Fig. 6.68), the activity of ruthenium catalyst increases from 9.33% to 15% when the H2/N2 ratio is 3 and 0.5, indicating that the relative activity increases by 60%. Fishel et has also investigated the effect of H2/N2 ratio on the turnover frequency of ammonia (TOF). Similar results are shown in Fig. 6.69. The TOF increases in linearity with decrease of H2 molar fraction and increase of N2 molar fraction at 350° C. 

The influence of preparation procedure on structural and surface properties of magnesium fluoride support and on the activity of ruthenium catalysts for selective hydrogenation of chloronitrobenzene... 

Novel catalytic systems, initially used for atom transfer radical additions in organic chemistry, have been employed in polymer science and referred to as atom transfer radical polymerization, ATRP [62-65]. Among the different systems developed, two have been widely used. The first involves the use of ruthenium catalysts [e.g. RuCl2(PPh3)2] in the presence of CC14 as the initiator and aluminum alkoxides as the activators. The second employs the catalytic system CuX/bpy (X = halogen) in the presence of alkyl halides as the initiators. Bpy is a 4,4/-dialkyl-substituted bipyridine, which acts as the catalyst s ligand. 

We found little difference between the activities of this catalyst with K2CO3 and with KOH. However, a pronounced dependence on pressure was seen for a six-fold decrease in CO pressure, the activity increased by a factor of 2.5. This tendency is in marked contrast to the activity increase with increasing CO pressure observed with ruthenium carbonyl. 

There is much current excitement and activity in the field of homogeneous hydrogenation using ruthenium catalysts. This is reflected in the recent, explosive increase in the number of research publications in this area, now rivaling those for rhodium catalysts (Fig. 3.1). Meanwhile, the price of rhodium metal has risen dramatically, becoming about ten times that of ruthenium, on a molar basis. The number of reports on the use of osmium catalysts has remained low, partly because of the higher price of osmium compounds - about ten times that of ruthenium - and partly because the activity of osmium catalysts is often lower. 

Water has been shown to enhance the activity of ruthenium and rhodium catalysts in both the TEAF and potassium formate systems [34, 36, 52]. The aqueous systems enable much simpler control of pH this is important, as Xiao has found that a low pH markedly slows the reaction [52]. The pH at which this occurs corresponds with the pKa of formic acid (i.e., 3.7), implying that the formate anion is required for complexation with the catalyst. Xiao has proposed two possible catalytic cycles - one that provides poor ee-values at low pH as a result of ligand decomplexation, and another that gives high ee-values at high pH. 

The behaviour of the ruthenium catalysts is quite different from that previously reported for cobalt carbonyl catalysts, which give a mixture of aldehydes and their acetals by formylation of the alkyl group of the orthoformate (19). The activity of rhodium catalysts, with and without iodide promoters,is limited to the first step of the hydrogenation to diethoxymethane and to a simple carbonylation or formylation of the ethyl groups to propionates and propionaldehyde derivatives (20). 

The activity of this ruthenium system is comparable to, or somewhat greater than, that of cobalt catalysts under the same conditions of temperature and pressure. Rhodium catalysts provide substantially higher activity than either of these systems. As will be seen later, however, addition of ionic promoters can greatly increase the activity of ruthenium-based catalysts. 

In this context, it is noteworthy that Over and co-workers (46,164-167) found the same types of Mars-van Krevelen mechanism for CO oxidation for ruthenium. Although the active surface was not characterized directly under high-pressure conditions in these investigations, it was found for the ruthenium(0 0 01) surface, which forms a RuO2(l 1 0) thin film in an oxygen-rich environment, that the activity of ruthenium as an oxidation catalyst is in fact primarily related to the RUO2 phase. 

In Section 6.3.6, it was emphasized that C02 and secondary amines could add to terminal alkynes in the presence of ruthenium catalysts to afford carbamates. Under comparable conditions (393-413 K, 5 MPa Ru-catalysts), primary amines will afford symmetrical disubstituted ureas in moderate yield [131]. It is worth noting that although the final urea does not contain the starting alkyne, its catalytic formation requires, besides the Ru-catalyst, the presence of a stoichiometric amount of a 1-alkyne (e.g., a propargylic alcohol). A possible mechanism (Scheme 6.32) for this catalytic reaction may involve activation of the alkyne at the metal center, a nucleophilic addition of the carbamate to the activated alkyne to produce... 

Prins reaction Conjugated dienes and activated alkenes react with aldehydes and carboxylic acids in the presence of ruthenium catalysts to give 1,3-diols. Variable amounts of acetoxybutene and higher molecular weight compounds can be formed. RuCl3 3H2Ocan be used, but the best results are obtained with 1. 

There are a number of indications in the literature that might make a reconsideration of their results worthwhile. The authors assume in their model that the intrinsic selectivity and activity of the catalyst does not change over the synthesis period. However, it is shown by Ponec et al. (6), that the catalyst is slowly activated during the synthesis. This activation is accompanied by changes in the selectivity. Ponec et al. attribute these changes in the behaviour of ruthenium catalysts to the deposition of carbon, and not to the low intrinsic propagation activity of the catalyst. Furthermore, Madon (7) showed that the simple Flory-Schulz distribution does not apply to ruthenium catalysts. The applicability of the Schulz-Flory law, however, is an essential part of the treatment of Dautzenberg and coworkers. 

With the exception of a few specific examples, the combination of ruthenium catalysts with hydrogen peroxide has not led to viable systems owing to rapid, competing decomposition of the hydrogen peroxide. If the activity of ruthenium with hydrogen peroxide could be tamed this would afford attractive... 

Pairs A and B were assigned to adsorbed SO and sulfide bonded to ruthenium atoms, respectively. The activation of Ru catalysts was dependent on the heating temperature of catalysts. Pair B appeared when the catalysts were still inactive. Hence, ruthenium metal microparticles were first sulfided and then exhibited the catalytic reactivity to form elemental sulfur from SO. The difference of sulfidation temperature for the [Ru CjA iOj (503 K) and conv-Ru/TiO catalysts (573 K) may be originated from each Ru particle size. In general, smaller [RuJ cluster is more reactive than larger Ru particles (10 - 50A) of conventional catalysts [14]. Pair A was exclusively observed in addition to the weak shoulder peaks of Pair B (Fig. lA). Therefore, the surface during the catalysis of the SO + Hj reactions should be predominantly occupied by SO. The elementary step of SO dissociation to SO(ads) may be the rate-determining step of overall reaction. 

It can be shown that by integration of Equation (6) and by plotting log t vs. log Phj for data obtained at constant temperature, the slope of the line drawn through the experimental points should be equal to 1 — w. It was found that this slope is approximately zero, the corresponding n being unity. Equations (3) and (5) can therefore be used to fit the experimental data obtained for ruthenium, rhodium, and platinum catalysts, on the assumption that the derived reaction mechanism is similar on all three catalysts. Since the activity of palladium catalyst was found very low and since it is believed, as will be discussed later, that palladium hydride is formed during catalysis, no values of k were computed for this catalyst. The values of k computed from the experimental data by means of Equation (5) are reported in Tables I-IV. These values are sufficiently constant to justify the proposed reaction mechanism. 

Due in large part to the development of ruthenium catalysts, olefin metathesis reactions can now be carried out on a diverse array of functionalized electron-rich and electron-poor olefins. As we have described, mechanistic analysis was instrumental in the design of more highly active second generation catalysts with expanded substrate scope, which was achieved by proper differentiation of the two L-type ligands within the (L)2(X)2Ru=CHR framework. Further investigations have revealed that these new catalysts display several unexpected features, and mechanistic analysis continues to be an invaluable tool for understanding reactivity patterns and for the development of new catalyst systems. 

The hydrogenation of unfunctionalised ketones has, in the past, proved challenging. However, Noyori and coworkers have discovered that the activity of ruthenium-based ketone hydrogenation catalysts can be greatly improved on incorporation of... 

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