Ru-catalyzed methanation

When activated carbon is used as support, the support degradation by Ru-catalyzed methanation imder ammonia synthesis conditions can occur, so it affects the fife of catalysts. Therefore, many researchers have tried to use metal oxides to replace the activated carbons as the supports for ruthenium catalysts. Supported catalysts with high dispersion and high activity can be obtained when noble metals in precursor forms are supported on hardly reduced metal oxide. The oxides which are commonly used as ruthenium catalyst support include oxides of alkaline earth metals, lanthanide,and alumina. ... 

There are much more serious problems of the catalyst with graphitized activated carbon as support at high hydrogen partial pressure due to the support degradation by Ru-catalyzed methanation under ammonia synthesis conditions. Despite so many... 

In addition, the catalyst appeared very stable under the reaction conditions little carbon was deposited on the spent catalyst. Other supported metals were less active. The activity order, Ru Rh > Ni > Ir > Co > Pt > Pd > Fe, is very comparable to that measured for the steam reforming of methane. Of all the supports tested, Y203 and Zr02 gave the best results for the Ru-catalyzed steam reforming of glycerol. 

Two extremes emerge from comparison of the Group VIII metals Ni, Rh, Co, and Ru (the left corner of the Group VIII metal block of the periodic table) prefer terminal splitting, already show multiple splitting at rather low temperatures, are the best catalysts (with Os) in hydrogenolysis of ethane (only 2C complexes possible), and catalyze well the reaction of carbon atoms to methane. Pt is the other extreme in all of these respects, with Pd and Ir... 

Methanol homologation catalyzed by ruthenium has been studied by Braca etal. [86, 89, 90]. Catalyst systems such as Ru(acac)3/Nal and Ru(C0)4lj/NaI have been shown to be active. In contrast to cobalt catalysts, no reaction occurs in the absence of 1" and a proton supplier is needed. As can be taken from Table XI, the reaction is higidy selective to C -products and no higlter products are formed. Due to the high hydrogenation activity of ruthenium, however, methane and ethane arc formed as side products in considerable amounts as well as dimethyl ether. Thus, the overall yield of ethanol is limited. The same catalyst systems have also been shown to be active in the homologation/carbonylation of ethers and esters. 

Carbon Monoxide-Hydrogen. - The reactions between CO and H2have been reviewed in the present series and previously by Vannice, who noted the paucity of studies with well defined alloys, although in both reviews it was possible to include CO adsorption/desorption and i.r. measurements involving alloys and bimetallic catalysts. The intrinsic importance of the catalyzed reaction makes it likely that much more work with bimetallic catalysts will be reported as indicated by the latest literature. The supported metals differ considerably in terms of product formation (which is also dependent on reaction conditions), methane (Ni), olefins (Ru, Co, and Ir), > C4 products (Co, Fe), and paraffin waxes (Ru), and it is tempting to suppose that bimetallics would combine desirable properties. 

Ru(Me)(Tp)(CO)(NCMe)] also promotes C-H bond activation at the 2-position of furan and thiophene yielding methane and [Ru(Ar)(Tp)(CO)(NCMe)] (Ar = 2-furyl or 2-thienyl). [Ru(2-thienyl)(Tp)(CO)(NCMe)] and [Ru( x-C,S-thienyl)(Tp)(CO)]2 were characterized structurally. [Ru(2-furyl)(Tp)(CO)(NCMe)] also catalyzes the formation of 2-ethylfuran from ethylene and furan. DFT calculations have been performed on the C-H activation of furan by Ru(Me)(Tab)(CO) (Tab = tris(azo)borate).333... 

This reaction is considered as a model of the catalytic reaction. In this work, CpM(CO)2[B(OR)2] (M=Fe, Ru,or W) was employed as a catalyst. Interestingly, the reaction proceeds through the oxidative addition and the reductive elimination for both methane and benzene in the W complex, where the W(V) complex is involved as an intermediate. On the other hand, the Fe-catalyzed reaction proceeds in one step for both methane and benzene, where the Fe(V) species is not involved as an intermediate but the Fe center takes +V oxidation state in the transition state. Thus, the reaction is considered to be metathesis. In the Ru complex, the reaction proceeds through the Ru(V) intermediate for the C-H o-bond activation of benzene, while it proceeds in one step for the C-H o-bond activation of methane hke that of the Fe complex. The differences among three metals can be interpreted in terms of the d orbital energy and/or the d" d" s promotion energy, as discussed above. 

In conclusion, CO hydrogenation catalyzed by Ru-Co bimetallic melt catalysis may lead to the formation of four classes of product (a) alcohols, including methanol, ethanol and propanol, (b) esters, mainly methyl acetate and ethyl acetate plus smaller quantities of propyl acetate and propionate esters, (c) acids, acetic acid, and (d) hydrocarbons, methane. 

Applications of molybdenum-based catalysts for CO-H2 reactions have received much attention since workers at the U.S. Bureau of Mines (111) reported high rates of molybdenum catalysts for methanation, exceeded only by those of the most active group 8 metal catalysts (Fe, Co, Ni, and Ru). Moreover, they were relatively resistant to sulfur poisoning and could simultaneously catalyze the water gas shift reactions during hydrocarbon synthesis, thus allowing a CO-rich gas mixture to be used. Recently, studies have been extended to various molybdenum compounds and supported catalysts (45,49,106,112). The turnover rates based on CO chemisorption for supported and unsupported molybdenum carbides (0.04-0.131 s ) were higher than for corresponding Mo metal (0.02 s ) at 570 K and atmospheric pressure (95,113). Oxides, sulfides, and nitrides of molybdenum were reported to exhibit somewhat lower turnover rates than metal or carbide counterparts (112). These values are comparable to those of Ru (0.03-0.77 s ), Ni (0.066 s ), and Co (0.09 s ), which are known as the most active catalysts for these reactions (114). 

The reaction is catalyzed by Co carbonyls using reaction conditions in the range 200-250 bar and 175-210°C, and, when first reported, was characterized by both low yields (maximum 42%) and a spectrum of by-products including acetaldehyde, methyl formate, methyl acetate, propanol, butanol, and methane (17). Subsequently, catalytic activity toward hydrocarbonylation has been demonstrated with other metals, although Rh, usually appreciably more active than Co in other synthesis gas reactions, produces acids and esters, and ethanol only comprises a significant product at high H2 partial pressures. Methanol hydrocarbonylation may also be carried out with Fe or Ru catalysts promoted by tertiary amines, but the rates are even lower than with Co, which remains the preferred choice. The reaction rate is accelerated by the presence of promoters such as I , in which case acetaldehyde (which may also be obtained from the Co/I -catalyzed reaction of synthesis gas with methyl ketals or methyl esters (18)), comprises the major product. 

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