Ruthenium, deposition

Figure 4-1 is a voitammogram of ruthenium deposited chemically on a platinum wire, in 3 M sulfuric add. It seems that the deposition was thick enough to cover the surface totally because there are no features of platinTun. Therefore, the voitammogram provides for a pure ruthenium electrode. 

Chemical analysis of solids and solutions indicate that in all cases metallic ruthenium, platinum, and gold are deposited on copper. Ruthenium, deposit is restricted to approximately 0.33 of the copper surface atoms, demonstrating that the redox reaction between Cu and Ru3+ can occur only on some special copper sites [11]. With platinum or gold, for the highest amount of modifier introduced (M"+/Cu(s) > 100), a deposit larger than a monolayer is obtained, indicating that all accessible copper atoms and subsurface copper atoms are involved in the redox reaction [13]. 

According to the standard electrochemical potentials (Table 1), with Cu/Cu2+ and Ru/Ru3+ couples, the amount of ruthenium deposited on metallic copper will be small, whereas the redox reaction carried out in presence of platinum or gold salts will occur to a large extent. On the other hand, for electrodes of first type (metal immersed in a solution of a salt of that metal), the standard electrochemical potentials as defined by thermodynamics are calculated with regard to a poly-crystalline metallic phase of infinite size. However, in the case of small metallic particles, characterized by metallic atoms of different coordination numbers, the notion of a local potential can be introduced. That no-... 

One may conclude that metallic bismuth overlayers deposited by MVD in the UHV environment or through UPD/dipping in the electrochemical environment are very similar in structure. A similar correspondence between the structures of ruthenium deposited by the two methods on Pt(lll) is demonstrated below, but only following the gas-phase reduction of the solution-deposited ruthenium phase with hydrogen. 

Figure 13 Ruthenium coverages on (a) Pt(llO) and (b) Pt(lll) estimated from LEISS (circles) and XPS (squares). The temperature corresponds to the temperature at which the surfaces have been annealed following ruthenium deposition by MVD. (From Refs. 86 and 94.)...

Figure 16 STM images of Pt(lll) electrode (at 100-mV bias) obtained after ruthenium deposition for 90s (top). Shown also are results of grain-size analysis of ruthenium island distribution for all islands (bottom left) and those from the analysis of bilayer ruthenium islands (bottom right). Ruthenium coverage is 0.19 ML. (From Ref. 105.)...

Thus, in summarizing this STM data, unlike the electrolytic deposition discussed in the previous section, where up to 0.7 monolayer (ML) coverage of ruthenium is deposited as mainly monoatomic islands with a tendency to create three-dimensional deposits as the coverage increases, when spontaneous deposition is used, about 10% of the islands are no longer monoatomic. Instead, such islands have a bilayer character, displaying a second monolayer deposit over the first monolayer. The result that such bilayer islands are formed at low coverage is related to the composition and morphology of the ruthenium deposits formed under a variety of electrochemical conditions. 

Htos (300 mL). The purple band is eluted with the 1.2 M Htos solution. The band is collected and concentrated under vacuum at 40°C until precipitation occurs (ca. 120 mL), which requires ca. 9h. The solution is left overnight at 0°C to allow for more complete precipitation. The solution is then filtered under argon, and the pink fluffy needles are washed with degassed ethyl acetate (2 x 20 mL) and then diethyl ether (2 x 20 mL) and dried in vacuo. The filtrate is concentrated at 40°C, and a second fraction is obtained and worked up. Yield (two fractions) 3.3 g (50%, based on RuCIrvFLO). The apparatus was cleaned as usual, and the ruthenium deposit traces were eliminated by a 5% sodium hypochlorite solution. 

The main focus of this year s effort has been on the deposition and characterization of platinum-ruthenium films of various compositions produced by co-sputtering of the individual elements. The effect of ruthenium deposited by reactive cosputtering has also been studied. The sputtering chamber was modified with a linear drive to be able to produce films on graphite foils, porous carbon structures, and on membranes. Thin films were deposited on graphite foil electrodes and characterized by XRD, XPS, SEM and polarization experiments. 

Ruthenium deposited on aluminum oxide is very active with respect to the isomerization of ethylcyclopentane to 1,2- and 1,3-dimethylcyclopentanes. 

Mention should be made of the high activity of ruthenium deposited on alumina in the isomerization reaction both to methylcyclohexane and especially to the mixture of trans- and cis-1,2- and 1,3-dimethylcyclo-pentanes, the dimethylcyclopentane content in the cyclane-alkane portion of the catalysate obtained in the presence of this catalyst being 60%, of which 85-90% constituted frans-1,2Kiimethylcyclopentane. The cyclane-alkane portion of the catalysate obtained on contact with Pd-Si02 also contained 10 % dimethylcyclopentanes. 

In the case of powder bulk catalysts, Cu Raney was modified by direct redox reaction between reduced copper and the salt of a noble metal M (Ru, Pt and Au) [5, 7]. Typically the Cu-M bimetallic catalysts were obtained by mixing a freshly prepared Cu Raney with an aqueous solution of the noble metal salt. When the amount of M is in excess compared to the number of copper surface atoms, it appears that ruthenium deposition is restricted to approximately 1/3 of the copper surface atoms. For platinum and gold, a deposit larger than a monolayer is obtained, indicating that subsurface copper atoms are involved in direct redox reaction. This result is explained by the lower potential difference between copper and rathenium compared to those of copper and platinum or gold [7j. However, the reactions involved in the direct redox reaction may not be as simple as indicated in Section 9.2. A typical time distribution of ion concentrations in solution during the preparation of Cu-Pt is shown in Fig. 9.1. It can be observed that platinum ions disappear very rapidly from the solution while at the same time copper... 

The electrochemical deposition of a metallic-ruthenium film is very difficult compared with that of other platinum-group elements [46, 61, 91-93]. One of the reasons may be related to the comphcated electrochemistry of ruthenium deposition and the stability of the Ru-chloro complex [92]. For example, it has been reported that the RuCfi species in HCIO4 solution is decomposed partly into RuO +, in which Ru(IV) is present [94]. 

The controlled deposition of ruthenium on well-defined surfaces, such as Pt(hkl) [95-103] and Au hkl) [38-40], has been characterized by electrochemical measurements, Fourier transform infrared reflection-absorption spectroscopy (FT-IRRAS), XPS and STM measurements. The interest in these studies is mainly concentrated on the ruthenium modification of a platinum surface because of its extreme importance in electrocatalysis. It has been demonstrated that a ruthenium-deposited Pt( 111) substrate showed an extremely high activity in methanol oxidation compared to ruthenium-deposited Pt(hkl) electrodes with other crystallographic orientations [98, 99]. 

The studies of ruthenium deposition are mainly carried out by electrochemical and spontaneous (electroless) deposition procedures. Friedrich and colleagues found that the well-reproduced current-potential curves of ruthenium-modified Pt(lll) electrodes were obtained when... 

Fig. 18 In situ STM image (4000 X 4000 nm ) ofAu(lll) surface at +0.3 V in 0.05 M H2SO4 + 1.6 mM RuNO(N03)x(OH)y (x + y = 3). STM imagining was carried out in the 2000 nm region (shown by the white box) in the beginning when the potential was swept between +0.3 V and - 0.3 V (2 mV s ) for approximately 2 hr. When the imaging region was enlarged to 4000 nm, ruthenium deposition was observed outside of the tip-scan region [40].

There are some information in the literature about the ruthenium-based zeoBte catalysts mainly linked to Ru-Y and Ru-X systems used in CO hydrogenatbn or amnnonia synthesis [ IS171 All of these consider that ruthenium deposition takes place only through an bnb exchange. 

I.a.ruthenium deposition High purity L zeolite and APO-34 obtained in Na form txrording to [ 18-19] Aere used as supports. The L zeolite had a silbon-to-aluminium ratio 6.4 as characterized by X-ray difiracdon and elemental analysis. The APO-34 sieve had an aluminium-to-phosphorus ratio of 1.26, as it was characterized by the same methods. In H-form NH3-TPD indicated 0.391 mmol/ for zeolite L (3796 strong sites and 26% weak sites) and 0.192 for APO-34 31 % strong sites and 35% weak sites). As mthenium precursor RUCI3.3H2O (Riedel-de-Haen AG) was used. Prior to ruthenium depositbn, the zeolites were evacuated at 300 C to a few mm Hg to avoid ocdusbn of air or maintained in water for 6 hours. 

The increase of the 372 nm signal intensity for molecular sieves maintained for 6 hours in water before ruthenium deposition, after contacting with ruthenium solution, could be due to the quick hydrolysis process of ruthenium by OH groups eliminated from zeolitic surface. The variation of the pH shows an important increase in the case of L zeolite whereas in the case of APO-34 this increase is not important (Fgures 3 and 4). 

Between zeolite L and APO-34 there are important differences. Zeolite L typically exhibits high exchange site density comparatively with APO-34. This is consistent with the concentration of the OH groups that could easily interact during ruthenium deposition. 

The FTIR results revealed a strong reduction of the bands bcated in the region 450 - 490 cm These data should be also a proof of the feet that ruthenium deposition takes place in part through ionb exchange. Ruthenium deposition could generate a rigidization of O-Si-O or O-AI-O bonds, as it was observed from these measurements. In the same time a small decrease of the band located at 3600 cm" indicates an OH elimination. 

Lan and Tao [22] successfully applied a novel fuel cell type with an alkaline membrane to oxidize ammonia at room temperature. Compared to solid oxide fuel cells, the alkaline membrane fuel cell is less brittle and can be operated at low temperatures. As an advantage of alkaline membrane fuel cells over conventional alkaline fuel cells, no KOH-based electrolyte is needed. The researchers used two types of anodes first platinum and ruthenium deposited on carbon and sec-raid chromium-decorated nickel. The ammraiia sources were either ammraiia gas or a 35 wt% aqueous ammonia solution. 

Friedrich KA, Geyzers KP, Linke U, Stimming U, Stumper J. CO adsorption and oxidation on a Pt(lll) electrode modified by ruthenium deposition an IR spectroscopic study. J Electroanal Chem 1996 402 123-8. 

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