Adsorption on ruthenium

H. Jobic, M. Lacroix, T. Decamp M. Breysse (1995). J. Catal., 157, 414—422. Characterization of ammonia adsorption on ruthenium sulfide. Identification of amino species by inelastic neutron scattering. 

Although CO adsorption on ruthenium has received little attention, there have been at least two reported infrared studies of CO adsorption on oxide supported ruthenium. Lynds (131) reported bands at about 2080 and 2140 cm which appeared to be constant with surface coverage and showed little difference if the surface was either at room temperature for 80°K. Guerra and Schulman (112) had difficulty in observing distinct peaks on their silica supported ruthenium, but also suggested two bands—a strong one at about 1900 cm and a much weaker one at about 2000 cm"b The differences in metal concentration and environment within the samples are likely to be the primary cause of the variations observed. 

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]. 

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... 

The co-existence of at least two modes of ethylene adsorption has been clearly demonstrated in studies of 14C-ethylene adsorption on nickel films [62] and various alumina- and silica-supported metals [53,63—65] at ambient temperature and above. When 14C-ethylene is adsorbed on to alumina-supported palladium, platinum, ruthenium, rhodium, nickel and iridium catalysts [63], it is observed that only a fraction of the initially adsorbed ethylene can be removed by molecular exchange with non-radioactive ethylene, by evacuation or during the subsequent hydrogenation of ethylene—hydrogen mixtures (Fig. 6). While the adsorptive capacity of the catalysts decreases in the order Ni > Rh > Ru > Ir > Pt > Pd, the percentage of the initially adsorbed ethylene retained by the surface which was the same for each of the processes, decreased in the order... 

Dautzenberg et al. (3) have determined the kinetics of the Fischer-Tropsch synthesis with ruthenium catalysts. The authors showed, that because the synthesis can be described by a consecutive mechanism, the non steady state behaviour of the catalyst can give information about the kinetics of the process. On ruthenium they found that not only the overall rate of hydrocarbon production per active site is small, but also that the rate constant of propagation is low. Hence, Dautzenberg et al. find that the low activity of Fischer-Tropsch catalysts is due to the low intrinsic activity of their sites. On the other hand, Rautavuoma (4) states that the low activity of cobalt catalysts is due to a small amount of active sites, the amount being much smaller than the number of adsorption sites measured. 

The trend of the activation energies Tact (shown in the last column of Table 5) closely follows that of the adsorption energies of the CH and CH2 fragments on the two surfaces. Because the adsorption energies are much higher for the reaction on ruthenium than for that on cobalt, the barrier for reaction on ruthenium is also inferred to be higher. The transition state is late with respect to the nonassociated state. 

F. CO Adsorption on Gold, Nickel, Iridium, Iron, and Ruthenium Single... 

To clarify the mechanism of propylene adsorption on Ru-Co clusters the quantum-chemical calculation of interaction between it and Ru-Co, Ru-Ru, and Co-Co clusters were carried out. During the calculation it was assumed that carbon atoms of C-C bond are situated parallel to metal-metal bond. The distance at which the cluster and absorbable molecule begin to interact is characterized by the nature of active center. Full optimization of C3H6 molecule geometry confirms that propylene adsorbs associatively on Co-Co cluster and forms Jt-type complex. In other cases the dissociate adsorption of propylene is occurred. The presence of Ru atom provides significant electron density transfer from olefin molecule orbitals to d-orbitals of ruthenium in bimetallic Ru-Co- or monometallic Ru-Ru-clasters (independently on either the tertiary carbon atom is located on ruthenium or cobalt atom.). At the same time the olefin C-C bond loosens substantially down to their break. 

In contrast, the effect of the adsorbed and alloyed ruthenium on the electrooxidation of CO has shown that promotion of the reaction is only evident if ruthenium is present in the top surface layer. Hence the mediation of the oxidizing species by top-layer ruthenium in the provision of Pt-Ru ensembles, rather than the modification of CO adsorption by ruthenium, promotes the electro-oxidation reaction [85,86]. 

Abnormal Infrared Effects in CO Adsorption on Electrodes of Nanometer-Scale Thin Eilm of Ruthenium... 

ABNORMAL INFRARED EFFECTS IN CO ADSORPTION ON ELECTRODES OF NANOMETER-SCALE THIN FILM OF RUTHENIUM... 

An infrared study of CO adsorption on Ru-Au supported on magnesia suggested that this bimetallic behaves differently from Ru-Cu, with no evidence of Au segregation at the cluster surface, (nor separate Au clusters although ruthenium and gold are practically immiscible in the bulk). At temperatures below 383 K where the reaction between cyclopropane and hydrogen adopted routes to propane or methane + ethane, no interaction between Au and Ru containing up to 36% Au was evident from the kinetic parameters.However, a more complete examination (unpublished) of these catalysts by XPS, EXAFS, SAXS, and other techniques has been made and it is believed that the surface contained Ru atoms only. 

Actually, rhodium and iridium can be used as well as ruthenium in mixtures with palladium. The results, however, allow only the qualitative statement that olefins are significant intermediates. The presence of more than one olefin isomer and uncertainty of the precise ratios of formation and rates of migration preclude any quantitative estimate. The experiments with mixed catalysts were terminated after 20 to 50% conversion. The mixed catalysts not only gave higher yields of (raws-decalin but the actual concentrations of the octalins present in the reaction mixture were lowered owing to preferential adsorption on the palladium component. 

The nature of adsorbed hydrogen atoms is not precisely known. Polycrystalline platinum, palladium, and iridium show two major peaks for hydrogen upon potential sweep in the positive potential region (97), indicative of multiple adsorption states. Ruthenium and rhodium exhibit only one adsorbed state at the low-potential, weak adsorption region 102, 103. The surface coverage on the first group of metals varies approximately linearly with potential [Fig. 6 (97.9,5)], in accord with Eq. (24) for a Temkin isotherm. 

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