Lanthanide ruthenium oxide

Consequently, in the early 1990s, interest in the direct processes decreased markedly, and the emphasis in research on CH4 conversion returned to the indirect processes giving synthesis gas (13). In 1990, Ashcroft et al. (13) reported some effective noble metal catalysts for the reaction about 90% conversion of methane and more than 90% selectivity to CO and H2 were achieved with a lanthanide ruthenium oxide catalyst (L2Ru207, where L = Pr, Eu, Gd, Dy, Yb or Lu) at a temperature of about 1048 K, atmospheric pressure, and a GHSV of 4 X 104 mL (mL catalyst)-1 h-1. This space velocity is much higher than that employed by Prettre et al. (3). Schmidt et al. (14-16) and Choudhary et al. (17) used even higher space velocities (with reactor residence times close to 10-3 s). 

The partial oxidation reaction of methane to syn is mildly exothermic, in contrast to hi fy endothermic steam reforming. It could produce stoichiometric syngas for methanol synthesis in one step. It is an ideal process for producing methanol syn. Effective catalysts are needed to carry the reaction selective at mild temperatures. A recent finding by researchers at the University of Oxford indicated that the reaction could be carried out selective at 775°C (97+% selectivity at 94% conversion) using lanthanide ruthenium oxide or alumina-supported ruthenium catalysts, in contrast to more than 1200°C in conventional processes [62],... 

Rare earth oxides are useful for partial oxidation of natural gas to ethane and ethylene. Samarium oxide doped with alkali metal halides is the most effective catalyst for producing predominantly ethylene. In syngas chemistry, addition of rare earths has proven to be useful to catalyst activity and selectivity. Formerly thorium oxide was used in the Fisher-Tropsch process. Recently ruthenium supported on rare earth oxides was found selective for lower olefin production. Also praseodymium-iron/alumina catalysts produce hydrocarbons in the middle distillate range. Further unusual catalytic properties have been found for lanthanide intermetallics like CeCo2, CeNi2, ThNis- Rare earth compounds (Ce, La) are effective promoters in alcohol synthesis, steam reforming of hydrocarbons, alcohol carbonylation and selective oxidation of olefins. 

The lanthanide contraction, however, has also effects for the rest of the transition metals in the lower part of the periodic system. The lanthanide contraction is of sufficient magnitude to cause the elements which follow in the third transition series to have sizes very similar to those of the second row of transition elements. Due to this, for instance hafnium (Hf ) has a 4" -ionic radius similar to that of zirconium, leading to similar behavior of these elements. Likewise, the elements Nb and Ta and the elements Mo and W have nearly identical sizes. Ruthenium, rhodium and palladium have similar sizes to osmium iridium and platinum. They also have similar chemical properties and they are difficult to separate. The effect of the lanthanide contraction is noticeable up to platinum (Z = 78), after which it no longer noticeable due to the so-called Inert Pair Effect (Encyclopedia Britannica 2015). The inert pair effect describes the preference of post-transition metals to form ions whose oxidation state is 2 less than the group valence. 

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. ... 

Prom experiments of hydrogen adsorption at room temperature, Aika et al. found that when the molar ratio of Sm/Ru was 10, the adsorption amount of hydrogen will reduce to 1/3 of the origin, which indicates that there is a very strong interaction between ruthenium and lanthanide oxides. The chemisorption amount of hydrogen is not reduced obviously following the addition of CsOH on ruthenium surface. For example, when Sm/Ru =10.0, the H/Ru ratio will decrease to 0.18, while Cs/Ru = 10.1, the H/Ru ratio is 0.45. 

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