Carbon monoxide ruthenium-based catalysts

Another reason of the surface enrichments or loss is the formation of volatile compounds of a certain component of catalysts with reactants. For example, nickel can react with carbon monoxide in reactants to form the volatile and thermally unstable nickel carbonyl, which escapes gradually from the catalyst surface. The activated carbon supported ruthenium-based catalysts also loses obviously part of itself due to the volatilization of ruthenium oxides or the occurrence of methanation reactions of the activated carbon. 

The most successful class of active ingredient for both oxidation and reduction is that of the noble metals silver, gold, ruthenium, rhodium, palladium, osmium, iridium, and platinum. Platinum and palladium readily oxidize carbon monoxide, all the hydrocarbons except methane, and the partially oxygenated organic compounds such as aldehydes and alcohols. Under reducing conditions, platinum can convert NO to N2 and to NH3. Platinum and palladium are used in small quantities as promoters for less active base metal oxide catalysts. Platinum is also a candidate for simultaneous oxidation and reduction when the oxidant/re-ductant ratio is within 1% of stoichiometry. The other four elements of the platinum family are in short supply. Ruthenium produces the least NH3 concentration in NO reduction in comparison with other catalysts, but it forms volatile toxic oxides. 

Over the past 35 years, much has been learned about the electrooxidation of methanol on the surface of noble metals and metal alloys, in particular platinum and ruthenium [2, 4, 6, 7]. Significant overpotential losses occur in the reaction due to poisoning of the alloy catalyst surface by carbon monoxide. Yet, Pt-based metal alloys are still the most popular catalyst materials in the development of new fuel cell electrocatalysts, based on the expectation that a more CO-tolerant methanol catalyst will be developed. The vast ternary composition space beyond Pt-Ru catalysts has not been adequately explored. This section demonstrates how the ternary space can be explored using the high-throughput, electrocatalyst workflow described above. 

Studies of the behavior of supported ruthenium systems has been stimulated because of the finding that ruthenium appears to be the most active element, based on exposed surface atoms, for carbon monoxide hydrogenation (ref. 65). A number of workers have studied the dissociation of carbon monoxide and subsequent buildup of carbidic carbon on the various crystallographic faces of ruthenium (refs. 66-70). It has been shown that the carbidic carbon is easily hydrogenated and is thought to be a precursor for the hydrocarbon products, while the less reactive graphitic carbon is associated with catalyst deactivation (refs. 34,71-72). 

The carbonylation of methanol to give acetic acid, according to Eq.(l), based on the catalyst [Rh(CO)2I2], is a major industrial process (Monsanto acetic acid process). However, ruthenium clusters as catalysts seem to favor the insertion of carbon monoxide into the O-H and not into the C-O bond, according to Eq.(2). Ru3(CO)12 in basic solution converts methanol to methyl formate with 90% selectivity (400-450 bar CO,... 

The yields reported with ruthenium catalysts are lower than with palladium catalysts. Mukherjee et al. reacted nitrobenzene with carbon monoxide and methanol with a sodium methoxide plus ruthenium catalyst to give 80% carbamate and 18% aniline.55 Based on the mechanism suggested by Giannoccaro et al., it should be possible to recycle the aniline to the next run. Gargulak et al. used a Ru((C6H5)2PCH2CH2P(C6H5)2)(CO)3 catalyst with nitrobenzene to prepare the carbamate.56 They felt that their catalyst is an improvement over the short lifetimes of earlier ones. 

In the above reactions, the oxidation process takes place in the anode electrode where the methanol is oxidized to carbon dioxide, protons, and electrons. In the reduction process, the protons combine with oxygen to form water and the electrons are transferred to produce the power. Figure 9-1 is a reaction scheme describing the probable methanol electrooxidation process (steps i-viii) within a DMFC anode [1]. Only Pt-based electrocatalysts show the necessary reactivity and stability in the acidic environment of the DMFC to be of practical use [2], This is the complete explanation of the anodic reactions at the anode electrode. The electrodes perform well due to the presence of a ruthenium catalyst added to the platinum anode (electrode). Addition of ruthenium catalyst enhances the reactivity of methanol in fuel cell at lower temperatures [3]. The ruthenium catalyst oxidizes carbon monoxide to carbon dioxide, which in return helps methanol reactivity with platinum at lower temperatures [4]. Because of this conversion, carbon dioxide is present in greater quantity around the anode electrode [5]. 

Lee et al. [58] from Samsung reported development of a fixed-bed natural gas reformer coupled to a WGS reactor with an electrical power equivalent of 1 kW. The steam reformer was placed in the center of the subsystem, while the annular WGS fixed bed surrounded the reformer separated by an insulation layer. Commercial ruthenium catalyst served for steam reforming, while a copper-based catalyst was used for WGS. A natural gas burner supplied the energy needed by steam reformer. The reformer was operated between 850 and 930 C, while the shift reactor worked between 480 and 530 C. The carbon monoxide content of the reformate was reduced to 0.7 vol.% downstream the shift reactor despite its high operating temperature, because the reformer was operated at high S/C ratio between 3 and 5 the water surplus affected the equilibrium of the WGS reaction positively. At full load, the efficiency of this subsystem was 78% which decreased to 72% at 25% load. 

Of the non-precious metal catalysts, the sample composed of pure hopcalite showed the highest activity achieving almost full conversion in the temperature window between 130 and 160 °C. The minimum CO concentration achieved was 40ppm. Of the precious-metal catalysts, the platinum/ruthenium samples showed the highest activity, namely more than 99.8% conversion. In particular, the platinum/ruthenium sample based upon the hopcalite carrier showed even higher conversion in the wide temperature window between 90 and 160 °C 7 ppm carbon monoxide were detected in the purified reformate [328]. However, hopcalite is not stable towards moisture, which would generate problems in practical applications [329]. 

Rosa et al. [251] set up a complete 5-kW diesel fuel processor based on autothermal reforming and catalytic carbon monoxide clean-up, which was dedicated to a low temperature PEM fuel cell. The breadboard system was composed of the autothermal reformer operated between 800 and 850 °C with a ruthenium/perovskite catalyst (see Section 4.2.8), a single water-gas shift reactor containing platinum/titania/ceria catalyst operated between 270 and 300 °C (see Section 4.5.1), and a preferential oxidation reactor containing platinum/alumina catalyst operated between 165 and 180 °C. Figure 9.54 shows the gas composition and reactor temperatures achieved. The hydrogen content of the reformate was in the range from 40 to 44 vol.% on a dry basis. The carbon monoxide content of the reformate was 7.4 vol.% and could be reduced to values of between 0.3 and 1 vol.% after the water-gas shift reactor and to below 100 ppm after the preferential oxidation reactor. 

Recently, blocked polymeric isocyanates useful in the preparation of polyurethanes, have been prepared by direct carbonylation of a nitro-substituted polymer based on styrene with carbon monoxide in the presence of a catalyst at 60-200 "C and a pressure from atmospheric to 2000 psi in a hydrogen-donor solvent [64]. Catalysts such as PdL2X2 (X = halogen, L = heterocyclic ligand, e.g. pyridine) in the presence of [NEt4][Cl] have been used. However, from the abstract it is not clear if polynuclear ruthenium, iron, and platinum carbonyls are... 

In order to produce methanol the catalyst should only dissociate the hydrogen but leave the carbon monoxide intact. Metals such as copper (in practice promoted with ZnO) and palladium as well as several alloys based on noble group VIII metals fulfill these requirements. Iron, cobalt, nickel, and ruthenium, on the other hand, are active for the production of hydrocarbons, because in contrast to copper, these metals easily dissociate CO. Nickel is a selective catalyst for methane formation. Carbidic carbon formed on the surface of the catalyst is hydrogenated to methane. The oxygen atoms from dissociated CO react with CO to CO2 or with H-atoms to water. The conversion of CO and H2 to higher hydrocarbons (on Fe, Co, and Ru) is called the Fischer-Tropsch reaction. The Fischer-Tropsch process provides a way to produce liquid fuels from coal or natural gas. 

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