Ruthenium, adsorption

Ruthenium Adsorption and Filtering Total gas flow, scfm Dew point of gas, °C Adsorber operating temperature, °C Pressure drop across adsorbers, in. H O Final filter operating temperature, °C Pressure drop across final filters and adjacent piping, in. H2O... 

CNF-supported ruthenium catalysts were also prepared by the procedure of deposition-precipitation using RuN0(N03)3(H20)2 as precursor (36). In this case, the 5 wt % of Ru in solution could be deposited, and small ruthenium particles (1.1-2.2 nm) were obtained after reduction. Hydrolysis of the Ru precursor in solution leads to the cationic complex [RuN0(N03)2(H20)3]. The authors calculated that the ruthenium/adsorption site ratio was equal to 1.2, i.e., close to the ratio expected for one-to-one adsorption. Implicitly, they concluded to a mechanism of cation adsorption. However, they did not attempt to increase the Ru loading to check if there is really a limitation in the Ru loading due to the hmited adsorption capacity of support. 

SSIMS has also been used to study the adsorption of propene on ruthenium [3.29], the decomposition of ammonia on silicon [3.30], and the decomposition of methane thiol on nickel [3.31]. 

Zero-order desorption occurs if the rate of desorption does not depend on the adsorption coverage, as seen with relatively large silver islands on a ruthenium surface (Fig. 7.7), where the Ag atoms desorb from the edges of the island. As the 0" term in Eq. (12) vanishes, the curves exhibit a clearly recognizable exponential shape on the leading side. Such situations are rare. 

Fig. 6.2 Schematic representation of a Mo-containing ruthenium-clustered material. The indicated reaction paths represent (1) adsorption, (2) electrocatalysis, (3) desorption. (Adapted from [18])...

The synergistic elfect seen in Pt-Rn alloys has aronsed great interest, since it opened perspectives for their nse in efficient methanol fnel cells. Many studies were performed to elucidate the origins of this effect. Some workers believe that it is due to changes in the electron strnctnre of platinnm npon alloy formation with ruthenium. A popular interpretation is the bifunctional mechanism, according to which the organic species are preferentially chemisorbed on platinnm sites while the ruthenium sites facilitate the adsorption of the species needed for oxidation of the orgaiuc species. 

Other metals on silica supports have been investigated less extensively than platinum and nickel, and average particle diameters have only been estimated by gas adsorption methods, supported in a few cases by X-ray line broadening data. Thus, rhodium, iridium, osmium, and ruthenium (44, 45) and palladium (46) have all been prepared with average metal particle diameters <40 A or so, after hydrogen reduction at 400°-500°C. 

Adsorption is commonly used for catalyst removal/recovery. The process involves treating the polymer solution with suitable materials which adsorb the catalyst residue and are then removed by filtration. Panster et al. [105] proposed a method involving adsorbers made from organosiloxane copolycondensates to recover rhodium and ruthenium catalysts from solutions of HNBR. These authors claimed that the residual rhodium could be reduced to less than 5 ppm, based on the HNBR content which had a hydrogenation conversion of over... 

Figure 3.21 UPS spectrum of Xe physisorbed on Ru(OOl) showing the superposition of the Xe 5p levels with the d-band of Ruthenium. The position of the Xe 5pm peak with respect to the Fermi level of Ru is a measure of the work function of the adsorption site, as the potential diagram indicates (from Wandelt et al. L54J).

A comparison of CO desorption from ruthenium (6), and from multilayer (10 ML) and monolayer copper covered ruthenium is shown in Figure 1. The CO coverage is at saturation. The TPD features of the 1 ML copper (peaks at 160 and 210 K) on ruthenium are at temperatures intermediate between those found for adsorption on surfaces of bulk ruthenium and copper, respectively. This suggests that the copper monolayer is perturbed electronically and that this perturbation is manifested in the bonding of CO. An increase in the... 

Ruthenium was electrochemically deposited on platinum foil at a potential of 50 mV for 10 s. The cyclic voitammogram of this Pt—Ru electrode in 3 M H2SO4 is shown in Fig. 4—2. The voitammogram shows the hydrogen adsorption-desorption features from 50 mV to 200 mV and the oxidation and reduction current over 300 mV. The voltanunogram seemed stable when the upper limit potential was 800 mV. When the upper limit was higher than 800 mV, the voitammogram became slowly like pure... 

Ruthenium/carbon catalysts have also been promoted by the addition of Fe. Bron et al. reported the addition of Fe to a preformed Ru/C catalyst via adsorption of Fe complexes, followed by heat treatment. They found an increase in oxygen reduction activity of three to five times over unmodified Ru/C. It was suggested that the surfaces of Ru particles were covered with FeN,Cy sites. As discussed previously, the Pd alloys have shown significant MeOH tolerance toward oxygen reduction and appear to have activities closest to that of Ft. 

An improved adsorption of DNA bases has been observed at a chemically modified electrode based on a Nafion/ruthenium oxide pyrochlore (Pb2Ru2-x FhxOj-y modified GC (CME). Nafion is a polyanionic perfiuorosulfonated ionomer with selective permeability due to accumulation of large hydrophobic cations rather than small hydrophilic ones. The Nafion coating was demonstrated to improve the accumulation of DNA bases, while the ruthenium oxide pyrochlore proved to have electrocatalytic effects towards the oxidation of G and A. The inherent catalytic activity of the CME results from the Nafion-bound oxide surface being hydrated. The catalytically active centers are the hydrated surface-boimd oxy-metal groups which act as binding centers for substrates [50]. 

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