Ruthenium, reactions over

Alkylation lo yield a leriiary amine may occur easily if the formation involves cyclization (ii). Catalysts may have a marked influence. In reductive alkylation of ammonia wilh cyclohexanones, more primary amine was formed over Ru and Rh and more secondary amine over Pd and Pt. Reduction of the ketone to an alcohol is an important side reaction over ruthenium. 

The above apparatus has been used to study reactions over single crystals of nickel, ruthenium, and rhodium (1-7,12-15). 

The above described experiments over atomically clean single crystal catalysts have been extended to studies of the kinetics of various catalytic reactions over chemically modified catalysts. Examples are recent studies Into the nature of poisoning by sulfur of the catalytic activity of nickel, ruthenium, and rhodium toward methana-tlon of CO (11,12) and CO2 (15). ethane (12) and cyclopropane (20) hydrogenolysls, and ethylene hydrogenation (21). 

Hexaruthenium carbonyl complexes have been used to prepare Ti02-supported mthenium catalysts for the sulfur dioxide reduction with hydrogen [112, 113], A catalyst derived from [Ru6C(CO)i6] showed higher activity in the production of elemental sulfur at low temperatures than that prepared from RUCI3 as precursor. This catalytic behavior is related with the formation of an amorphous ruthenium sulfide phase that takes place during the reaction over the ex-carbonyl catalyst [112]. 

Dialkyl ketones, especially sterically hindered ones, tend to give the corresponding alcohols to significant extents under conditions of reductive amination, resulting in lower yields of amines. As in the cases of the aromatic ketones described above, the addition of small amounts of acetic acid or ammonium acetate is effective to depress the formation of alcohols, which may become a significant side reaction over those catalysts that are active for the hydrogenation of ketones to alcohols such as ruthenium, Raney Co, and Raney Ni.17 Thus, the formation of 2-nonanol could be depressed effectively in the presence of ammonium acetate in the reductive amination of 2-nonanone over these catalysts (eq. 6.7). 

Smface modification with ruthenium complexes has proven valuable in studies of both interprotein and intraprotein electron transfer in systems that are difflcult to stndy by traditional kinetic tools. The choice of ruthenium complexes in these investigations stems from an extensive photochemistry as well as exceptional thermal stability. The photochemistry provides a means of examining reactions over a time range of nanoseconds to seconds by laser-flash photolysis and the thermal stability allows researchers to covalently bind a wide variety of complexes to proteins with... 

The kinetics of ADMET with complex 6 were compared to those of complex 2 by measuring the volume of ethylene liberated from ADMET reactions over time [35], Obtaining an approximate second order rate constant from the DP versus time curves, it was found that molybdenum complex 2 polymerizes 1,9-decadiene 24 times faster than ruthenium complex 6 (Tab. 6.1). 

This mechanism seems adequate to describe the reactions over ruthenium, osmium, iridium, and rhodium (in certain instances) which exhibit an order of unity in hydrogen. 

Similarities do exist between the reaction over iron- and mthenium-based catalysts. For instance, it has been well established that alkali metals act as chemical promoters on both iron [1.7] and ruthenium [5,12]. This chemical promotional effect is due to the electron donating... 

Surface-science studies using nickel single-crystal surfaces revealed that the methanation reaction is surface-structure-insensitive. Both the (111) and (100) crystal faces yield the same reaction rates over a wide temperature range. These specific rates are also the same as those found for alumina-supported nickel, further proving the structure insensitivity of the process. This is also the case for the reaction over ruthenium, rhodium, molybdenum, and iron. 

Irrespective of the nature of the reaction intermediate, enolic type (11) or surface carbide (12), the dechne of the turnover number for the zeolites with higher Si/Al ratio can be explained as follows. For platinum (13) and palladium (14,15) loaded zeolites, support effects are known to exist. The higher the acidity (and the oxidizing power) of the zeolite, the higher will be the electron-deficient character of the supported metal. It also is well established now (16) that the average acidity of hydrogen zeohtes increases with the Si/Al ratio. This explains why the electron deficient character of ruthenium should increase with the Si/Al ratio of the zeolite, and a stronger interaction with adsorbed CO should be expected. Vannice (19,20) reported that the N value for CH4 formation decreases when the heat of adsorption for CO increases. All this explains why the tmnover number of the methanation reaction over ruthenium decreases when the Si/Al ratio of the zeolite support increases. 

Prom recent single crystal studies, DFT calculations, and studies of supported catalysts, it was found that ammonia synthesis reaction over ruthenium is an even more structure-sensitive reaction than over iron-based catalysts. In order to... 

In the CWAO of carboxylic acids, noble metals give the best performances and stability. Ruthenium supported over ceria-zirconia shows the best performance. These catalysts are also preferable for CWAO of N-containing compounds such as aniline. Over Ru/Ce02, ammonium ions formed in the reaction are selectively oxidized into molecular nitrogen in the temperature range of 180 to 200°C, but above 200°C nitrite and nitrate ions form. 

In the 1970s, a catalyst system promoted by metallic potassium [73, 74] was studied. The ammonia synthesis rates at 80 kPa and 588 K over transition metals supported on active carbon and promoted by metallic potassium are given in Fig. 3.2 [69]. The activity of isotopic equilibration of N2 over the same series of catalysts at 30 kPa of N2 and at 588 K are shown in Fig. 3.3 [75]. The same reaction over Raney metals are also shown in this figure [76]. In these cases ruthenium is the most active metal. There is a common belief that Fe, Ru and Os are the most active elements in ammonia synthesis, ammonia decompo-... 

A Belgian patent (178) claims improved ethanol selectivity of over 62%, starting with methanol and synthesis gas and using a cobalt catalyst with a hahde promoter and a tertiary phosphine. At 195°C, and initial carbon monoxide pressure of 7.1 MPa (70 atm) and hydrogen pressure of 7.1 MPa, methanol conversions of 30% were indicated, but the selectivity for acetic acid and methyl acetate, usehil by-products from this reaction, was only 7%. Ruthenium and osmium catalysts (179,180) have also been employed for this reaction. The addition of a bicycHc trialkyl phosphine is claimed to increase methanol conversion from 24% to 89% (181). 

Reductive alkylation by alcohol solvents may occur as an unwanted side reaction 22,39), and it is to avoid this reaction that Freifelder (20) recom mends ruthenium instead of nickel in pyridine hydrogenation. Alkylation by alcohols may occur with surprising ease 67). Reduction of 18 in ethanol over 10% palladium-on carbon to an amino acid, followed bycyclization with /V,/V-dicyclohexylcarbodiimide gave a mixture of 19 and 20 wiih the major product being the /V-ethyl derivative 49,50). By carrying out the reduction in acetic acid, 20 was obtained as the sole cyclized product 40). 

The sequence has been applied to the synthesis of 1,4-cyclohexanedione from hydroquinone 10), using W-7 Raney nickel as prepared by Billica and Adkins 6), except that the catalyst was stored under water. The use of water as solvent permitted, after hltration of the catalyst, direct oxidation of the reaction mixture with ruthenium trichloride and sodium hypochlorite via ruthenium tetroxide 78). Hydroquinone can be reduced to the diol over /o Rh-on-C at ambient conditions quantitatively (20). 

The Degussa process, on the other hand, reacts ammonia with methane in absence of air using a platinum, aluminum-ruthenium ahoy as a catalyst at approximately 1200°C. The reaction produces hydrogen cyanide and hydrogen, and the yield is over 90%. The reaction is endothermic and requires 251 KJ/mol. 

Figure 4 shows the rate of ethane hydrogenolysls over a ruthenium catalyst as a function of H2 partial pressure (12). In agreement with studies on supported catalysts ( ), the reaction Is negative order with respect to hydrogen for partial pressures of H2 above 40... 

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