Ruthenium catalysts structure sensitivity

The platinum group metals demonstrate clearly the impact of the key parameters that influence the efficiency of ammonia synthesis catalysts structure sensitivity, the heat of adsorption of reactants and products, and the roles of promoters and supports. The key requirement to minimize the activation energy for nitrogen dissociation limits the active metals to alkali-promoted ruthenium and osmium. Similar activities are then obtained, irrespective of the genesis of the alkali metal promoter (salt or metal), indicating that both convert to a similar... 

An example for a non-structure-sensitive reaction is provided by Davis et al. [102], who investigated the liquid-phase hydrogenation of glucose over carbon and silica based ruthenium catalysts with particle sizes between 1.1 and 2.4 run. Depending on catalyst loading which was between 0.56 wt.% and 5 wt.%, dispersion decreased from 91% to 43%. At the same time, TOFs varied only insignificantly in a range between 0.21 1/s and 0.32 1/s. 

It is now widely accepted that the activation of CO is highly structure sensitive (II). The activation of CO on most of the transition metals has been investigated. The computational results for cobalt (6) and ruthenium (5) are of particular relevance to us because these elements in the metallic state are active for the Fischer-Tropsch reaction. These results can be compared with those obtained for rhodium (40), which selectively catalyzes the formation of alcohols from CO and H2, and for nickel (30), which is a methanation catalyst. 

The hypothesis that the high yields obtained in the bifunctional catalytic system is caused by adsorption of the sensitizer on the surface of the colloidal Ti02 particle lead to the discovery of relay free water decomposition systems350. The only components present in solution are a sensitizer and the catalyst. The sensitizers employed331 were ruthenium trisbipyridyl complexes of the structure ... 

Ruthenium has long been known to be an effective catalyst for ammonia synthesis. However, compared to the traditional iron-based catalysts, studies on ruthenium-based catalysts are limited. The rate determining step of ammonia synthesis, the dissociative adsorption of dinitrogen, has been shown to extremely structure sensitive on both iron and mthenium catalysts. To study this structure sensitivity on ruthenium, density functional theory calculations were performed on Ru(OOl) and Ru(llO) clusters. End-on, side-on, and dissociated adsorption states were investigated on both surfaces. While the Ru(llO) cluster could stabilize aJl three adsorption modes, a minimum energy structure for the side-on adsorption on Ru(OOl) could not be found. It is likely that this side-on mode can provide a low energy pathway to the dissociated state, thereby resulting in faster dissociative adsorption on Ru(llO). 

Whether on iron catalysts or ruthenium catalysts, ammonia synthesis reaction has been proved to be a structure-sensitive reaction, and has been discussed in literature. Ertl and Spencer made tremendous contributions to the final determination of reaction mechanism and structure-sensitivity. 

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... 

It is seen from the above analysis that there is close relationship between the activity of supported ruthenium catalyst and the particle size and shape, which is an obvious structural sensitive catalyst. 

One of the key points of Ru/C catalyst is the structure sensitivity for aimno-nia synthesis reaction. It is determined that the cost of final products can be controlled by the suitable ruthenium loading amount. Rossetti et found... 

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