Methanation ruthenium catalysts

Figure 2. A comparison of the rate (turn-over frequency) of methane synthesis over single crystal and supported ruthenium catalysts. Total reactant pressure for the single crystal studies was 120 Torr.

For each case we will also present catalytic analogues, namely (1) the activation of methane to form methanol with platinum, the reaction of certain aromatics with palladium to give alkene-substituted aromatics, and (2) the alkylation of aromatics with ruthenium catalysts, and the borylation of alkanes and arenes with a variety of metal complexes. 

A structured ruthenium catalyst (metal monolith supported) was investigated by Rabe et al. [70] in the ATR of methane using pure oxygen as oxidant. The catalytic activity tests were carried out at low temperature (<800 ° C) and high steam-to-carbon ratios (between 1.3 and 4). It was found that the lower operating temperature reduced the overall methane conversion and thus the reforming efficiency. However, the catalyst was stable during time on-stream tests without apparent carbon formation. 

Fig. 24. Products of an Hi-promoted ruthenium catalyst in tri-n-propylphosphine oxide, as a function of reaction time (193) (A) ethanol ( ) methane (O) methanol ( ) ethylene glycol (A) n-propanol. Reaction conditions 75 ml solvent, 15 mmol Ru, 15 mmol HI, 850 atm, H2/CO = 1,230 C.

Directly supported clusters of type Os3H(CO)10(O—metal oxide) break down at quite low temperatures to give species which have a high selectivity to methane from CO and H2 (381,400). Similar behavior has been reported for Os3(CO)12 itself (401), but it is difficult to rule out metal as the catalyst. Os3(CO)12 also leads to methanol, methyl and ethyl formate, and acetone by reaction with CO and H 2 (190° C, 180 atm) in glyme solvents (402). The water-gas-shift reaction is catalyzed by Os3(CO)12, using KOH or even sodium sulfide in methanol as the base (403), although ruthenium catalysts are better (404). 

In a reactor that is similar to a reformer, the reaction occurs in tubes that are heated externally to supply the endothermic heat of reaction129. Sintered corundum (a-Al203) tubes with an internal layer ( 15 microns thick) of platinum/ruthenium catalyst are used, hi some cases a platinum/aluminum catalyst may be used. To achieve adequate heat transfer, the tubes may be only % in diameter and 6V2 feet long. Selectivities of 90-91% for methane and 83-84% for ammonia are reached at 1200°C to 1300°C reaction temperatures. 

Comparison of Initial Methanation Activities for Zeolite and Alumina Supported Ruthenium Catalysts... 

As is showm in Figure 2, methane is formed over nickel and ruthenium catalysts, especially at low pressures (atmospheric up to 10 bar) and elevated temperatures. Paraffins and olefins are produced over nickel and cobalt catalysis at mild temperatures (< 200 0) and pressures of I -10 bar. With iron catalysts, olefins,parafllns.and minor amounts of alcohols are formed at medium pressures (10 100 bar) and temperatures of 210--340 C. Ruthenium catalysts give, at elevated pressures (150-1000 bar) and low temperatures (100-180 C), poly methylene with a molecular weiglii of up to I 000000. This polymer has similar properties as Ziegler-type low pressure polyethylene. 

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. 

The complete hydrogenation of carbon dioxide yields methane (and higlter hydrocarbons). Supported nickel catalysts were studied in detail [141 149] and ruthenium catalysts coated on membranes, molecular sieves or aluminum oxides are also very active in CO methanation (ISO I5S]. Intermeiallic compounds like FeTi, or rare earth and actinide intermeiallics,also catalyze the reduction of CO to at, [156 157]. 

Inui found an accelerating efiect of CO on carbon dioxide methanation over a supported nickel lanthanum oxide ruthenium catalyst [158] and a systematic comparison of the catalytic efficiencies of the atumina supported noble metals Pi, Pd, Kh. Ir and Ku was reported by Solymosi [tS9. He found that (he specific rates for the formation ofCH decrease in the order Ru > Kh > Pt - Ir - Pd. 

Methane is formed over nickel and ruthenium catalysts, especially at low pressure (up to 10 atm) and high temperature (220-340 °C). Nickel and cobalt catalysts yield paraffins and olefins at milder temperatures (<200 °C) and a pressure of 1-10 atm. Over iron catalysts, olefins, paraffins and small amounts of alcohols are formed at medium pressure (10-100 atm) and a high temperature of 210-340 °C. Ruthenium... 

In another brief examination [ 15] of the impact of monolith supports for mcthanation catalysts, a comparison between nickel and ruthenium catalysts was made utilizing a metal (Fecralloy) support. The conversion tests were run at 673 K, 5400 kPa, 3.47 sec", and with a gas composition of 62% hydrogen, 18% carbon monoxide, and 20% water vapor. A ruthenium pellet catalyst that was run in comparison was approximately twice as active as ruthenium on the monolith. However, the difference in product (methane) selectivity was 97% for the metal monolith catalyst and 83% for the pellet bed. In the comparison between nickel and ruthenium, shown in Fig. 14, the ruthenium was more active and selective. The lack of impact on activity or selectivity as a result of steam addition to the reactant mixture provided useful practical data as well. No further details regarding the catalyst characteristics were provided. 

The addition of MgO to activated carbon-supported ruthenium catalysts in an optimal Ru Mg ratio results in efficient catalyts for the CO2 reforming of methane, with stable selectivities towards CO and H2 production. 

Lanza R, Jaras SG, Canu P (2007) Partial oxidation of methane over supported ruthenium catalysts. Appl Catal A-Gen 325(l) 57-67... 

Table 7.13 INS spectra col cm" ) of surface hydrocarbon species formed in the decomposition of methane on supported nickel and ruthenium catalysts.

Most industrial catalysts have a high activity for the reforming reactions. It has been shown that nickel and ruthenium catalysts may be able to convert methane even at 300 C (6). This indicates that the activation of methane can hardly be the rate determining step nor the activation of the more reactive higher hydrocarbons at normal steam reforming conditions. 

We improved the WGS activity of cobalt- and ruthenium-based eatalysts while suppressing the methanation aetivity by adding a promoter. As shown in Figures 5 and 6, these catalysts are more aetive than commereial iron-chrome at temperatures >300°C. Our results indicate that the cobalt and ruthenium catalysts would be suitable replacements for iron-chrome as an HTS catalyst. 

We further developed a temperature-stable eopper/mixed oxide catalyst by fabricating it in a structured form that has the same activity as the powder. This catalyst can be activated in air and does not lose activity after exposure to air at temperatures up to 300°C. The ANL copper/mixed oxide catalyst has the potential to reduce the volume of the WGS reactor by 20% compared with the commercial catalysts. The copper catalyst showed susceptibility to poisoning by H2S in the reformate feed. We have also developed cobalt and ruthenium catalysts with higher activity than commercial iron-chrome (325-400°C) by using a promoter to suppress methane formation. 

Ruthenium Catalyst. The ruthenium catalyst studied was 0.5% ruthenium on 1/8-in. alumina pellets. Data in Table IV show that at low temperatures and low feed rate/catalyst weight ratios, this is an effective methanation catalyst. Higher hydrocarbon formation is, again, lower than expected, possibly owing to hydrogenolysis. Trace yields of oils containing paraffins, olefins, and aromatics were obtained. 

The third example involves the synthesis of methane from synthesis gas, CO and H2, over a ruthenium catalyst [8]. The overall reaction is... 

Carbon monoxide and carbon dioxide are poisons for many hydrogenation catalysts used in ammonia synthesis, refinery processes and petrochemical processes. Therefore, in steam reformers designed to produce hydrogen for hydrogenations, carbon oxides are removed to very low levels, typically a maximum of 5 ppm [7]. The conventional method of achieving this specification is to use a nickel or ruthenium catalyst to convert carbon oxides to methane. The conversion proceeds in accordance with the following methanation reactions ... 

Methanation Activity. AcnviTY and Selectivity. In Figure 1 are compared the methanation activity of 0.5 wt % Ru on NaY zeolite and on alumina, and 1% Ni on NaY zeolite. It is seen that the initial activity of the two ruthenium catalysts is comparable, while the nickel catalyst is... 

Progress on the addition of aromatic C-H bonds to olefins has been made by Periana with iridium catalysts - - and Gunnoe with ruthenium catalysts. - Both systems illustrate that the anti-Markovnikov addition products can be generated in larger quantities than the Markovnikov products, although mixtures of regioisomers are still observed. Intramolecular additions of the C-H bonds of electron-rich heterocycles to electron-deficient alkenes have also been reported (Equation 18.65). Most recently, Tilley has reported the addition of the C-H bond of methane across an olefin catalyzed by scandocene complexes. This reaction occurs, albeit slowly, with Markovnikov regiochemistry. 

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