Surface Concentration Of Ru Research Articles

Hydrogen production from ammonia decomposition over Ru-rich surface on La2O2CO3-Al2O3 catalyst beads

Three ruthenium-supported catalyst beads (Ru/Al2O3, Ru/La2O3-Al2O3 and Ru/La2O2CO3-Al2O3) were synthesized and tested for ammonia decomposition. The catalytic activity of the Ru/La2O2CO3-Al2O3 beads was significantly higher than that of the Ru/Al2O3 and Ru/La2O3-Al2O3 beads. This was primarily attributed to the addition of La, which encouraged electron donation from the bead surface to the Ru particles, increasing the rate of N2 desorption. In particular, a higher Ru surface concentration was achieved over the boundary layer of La2O2CO3 compared with La2O3. This is thought to be a result of steric hindrance, with the crystalline surface of La2O2CO3 acting as a structural stabilizer to significantly limit the penetration of Ru particles into the catalyst bead core. SEM-EDS line scanning of transverse sections of the catalyst beads confirmed a higher Ru concentration on the surface of the catalyst beads for Ru/La2O2CO3-Al2O3 compared with Ru/La2O3-Al2O3 and Ru/Al2O3. In fact, the ratio of surface/bulk Ru concentration in Ru/La2O2CO3-Al2O3 was more than twice that of Ru/Al2O3 at equal Ru loadings. The favorable properties of an La2O2CO3 surface-coating can benefit industrial catalyst synthesis, increasing the surface metal concentration compared with traditional La-based Al2O3 beads and pellets.

Ru-M (M = Fe or Co) Catalysts with high Ru surface concentration for Fischer-Tropsch synthesis

Ru-Co/Al2O3 and Ru-Fe/Al2O3 have been prepared by the reduction-deposition method. This approach favours the interaction between Ru and Fe or Co in the final catalysts, while increasing surface enrichment of Ru. Their performance for the Fischer-Tropsch Synthesis (FTS) has been evaluated in a fixed bed reactor. Ru-Co/Al2O3 displays the highest activity in the series, doubling the steady-state CO conversion rate of a Ru/Al2O3 catalyst with 3 times higher Ru loading. Ru-Fe/Al2O3 displays higher initial CO conversion and -CH2- productivity than Ru/Al2O3, but its activity declines during operation reaching lower conversion rates than Ru/Al2O3. In addition to CO2, Ru-Fe/Al2O3 produces oxygenated products, mainly alcohols. To a lesser extent, the formation of oxygenates over Ru-Co/Al2O3 and Ru/Al2O3 is also observed, and ascribed to the small crystallite size of the Ru particles. The evolution of CO2 during time on stream indicates that Fe is segregated to the surface of this catalyst during the FTS.

On the Origin of the Improved Ruthenium Stability in RuO2–IrO2 Mixed Oxides

High oxygen evolution reaction activity of ruthenium and long term stability of iridium in acidic electrolytes make their mixed oxides attractive candidates for utilization as anodes in water electrolyzers. Indeed, such materials were addressed in numerous previous studies. The application of a scanning flow cell connected to an inductively coupled plasma mass spectrometer allowed us now to examine the stability and activity toward oxygen evolution reaction of such mixed oxides in parallel. The whole composition range of Ir–Ru mixtures has been covered in a thin film material library. In the whole composition range the rate of Ru dissolution is observed to be much higher than that of Ir. Eventually, due to the loss of Ru, the activity of the mixed oxides approaches the value corresponding to pure IrO2. Interestingly, the loss of only a few percent of a monolayer in Ru surface concentration results in a significant drop in activity. Several explanations of this phenomenon are discussed. It is concluded that the herein observed stability of mixed Ir–Ru oxide systems is most likely a result of high corrosion resistance of the iridium component, but not due to an alteration of the material's electronic structure.

Hydrogen production by reforming of diesel fuel over catalysts derived from LaCo 1− xRu xO 3 perovskites: Effect of the partial substitution of Co by Ru ( x = 0.01–0.1)

LaCo 1− x Ru x O 3 perovskites with different substitutions of Co by Ru ( x = 0.01–0.1) have been investigated as precursors of catalysts for the oxidative reforming of diesel for hydrogen production. The physicochemical characterization of LaCo 1− x Ru x O 3 perovskites revealed modifications in their structure, crystalline size and surface area with the incorporation of ruthenium into the perovskite lattice. The modifications in the perovskites affect the structure and morphology of the catalysts obtained by reduction of perovskites prior the reaction. In the catalysts derived from ruthenium-containing perovskites it is observed a better reducibility, smaller particle size of La 2O 3 and Co 0 phases and better surface concentration of Ru 0 particles with the increase in the degree of Co substitution in the perovskite. The modifications in the characteristics of the catalysts induced by the Co substitution in perovskite directly affect their catalytic behaviour in the oxidative reforming of diesel. It is found that the greater Co 0 + Ru 0 exposition and the higher extension of the La 2O 2CO 3 phase achieved in catalysts derived from perovskites with higher cobalt degree of substitution produces an increase in the activity and stability of the catalysts derived.

Effect of Surface Segregation on the Methanol Oxidation Reaction in Carbon-Supported Pt−Ru Alloy Nanoparticles

Ru and Pt-Ru (Pt:Ru = 1:1) nanoparticles supported on carbon black were prepared by the borohydride reduction method using oleylamine as a stabilizer in an anhydrous ethanol solvent. We investigated the effect of Pt segregation to the surface of alloy nanoparticles on the methanol oxidation reaction (MOR). As-prepared Pt(1)Ru(1)/C showed a narrow size distribution and a relatively uniform particle distribution on a carbon support. However, its electrocatalytic activity toward the MOR was poor due to the high surface concentration of Ru. As duration time of heat treatment at 200 degrees C was increased up to 2 h, the surface composition of Pt atoms was increased without significant particle growth due to thermally induced segregation of Pt atoms, which were revealed by TEM images, X-ray photoelectron spectroscopy (XPS) analysis, changes in the potentials of zero total charge (pztc), and increase in the oxidation charge of "reduced CO(2)". In particular, from the combination of CO adlayer oxidation and "reduced CO(2)" oxidation charges, the increased surface concentration of Pt of alloy catalysts was relatively quantified when compared to its as-prepared state. Cyclic voltammograms in 0.1 M HClO(4) solution with 0.5 M methanol showed that Pt(1)Ru(1)/C annealed for 2 h at 200 degrees C in a flow of mixture gas of Ar and H(2) (5 vol %) had a less positive onset potential for the MOR. These results demonstrate a definitive contribution from segregation of Pt atoms to the MOR activity.

Pt promotion and spill-over processes during deposition and desorption of upd-Had and OHad on PtxRu1−x/Ru(0001) surface alloys

The electrochemical adsorption of underpotential deposited hydrogen (upd-H(ad)) and OH(ad) on structurally well-defined Pt(x)Ru(1-x)/Ru(0001) surface alloys was investigated by cyclic voltammetry and density functional theory (DFT) calculations. The adsorption energies of both upd-H(ad) and OH(ad) decrease with increasing Pt content in the adsorption ensemble, shifting the onset of upd-H(ad) and OH(ad) formation to increasingly cathodic and anodic potentials, respectively. For bare Ru(0001) and for Ru(3) sites in the surface alloy, the stability regions of these two species overlap or almost overlap, respectively. Similar to previous findings for upd-H(ad) adsorption/desorption on partly Pt monolayer island covered Ru(0001) surfaces (J. Phys. Chem. B 2004, 108, 14780), we find a sharp peak at approximately 100 mV vs. RHE in each scan direction, which is attributed to a Pt catalyzed OH(ad)<--> upd-H(ad) replacement on Ru(3) sites, via adsorption on Pt rich sites and spill-over to Ru(3) sites. The decrease of the integrated charge in these peaks with the third power of the Ru surface concentration, which for a random distribution of surface atoms reflects the availability of Ru(3) sites, supports the above assignment.

Electrochemical and spontaneous deposition of ruthenium at platinum electrodes for methanol oxidation: an electrochemical quartz crystal microbalance study

PtRu electrodes with Ru surface concentration ranging from 20 to 50% were prepared by electrolysis of Ru(NO)(NO 3) 3 at a constant potential and/or by spontaneous Ru deposition performed at open circuit potential from a RuCl 3 solution. The amount of either spontaneously or electrochemically deposited ruthenium on the platinum electrode was determined by means of an electrochemical quartz crystal microbalance (EQCM). The effect of the Ru surface concentration on the rate of methanol electrooxidation was also investigated and correlated to the EQCM measurements.

Ru/ZrO2 Catalysts: I. O2, CO, and NO Adsorption and Reactivity

The Ru/ZrO2 catalyst's surface properties have been studied by quantitative chemisorption experiments on carbon monoxide and oxygen at different temperatures, by FTIR studies of oxygen, carbon monoxide, and nitric oxide adsorptions, and by FTIR studies of the CO–NO reaction. On the oxidized sample at least three FTIR absorptions are evident at 1008, 980, and 950–940 cm−1. All the observed bands can be assigned to Ru–O surface species, differing in the oxidation state of ruthenium directly bonded to oxygen, the degree of metal–oxygen π bonding, and the coordination of the Ru atoms with the support. The larger heterogeneity of the bands observed on Ru/ZrO2 catalyst, with respect to that previously detected on Ru/ZnO, can be taken as an indication that a significant role is played by the coordination properties and the surface features of the support. The strong increase of the band at 1008 cm−1 at temperatures higher than 573 K can be ascribed to the increase of the surface concentration of Ru–O surface species bonded to an Ru atom with an oxidation state higher than 4. The CO adsorption on the oxidized sample evidences the full reactivity of Ru–O species toward CO between room temperature (RT) and 473. CO and NO chemisorptions on reduced samples show that the two molecules are both molecularly and dissociatively adsorbed on the catalysts. The NO admission on preadsorbed CO produces immediately a significant modification of the adsorbed CO spectrum, i.e., a reduction of the intensity of the band assigned to CO adsorbed on Ru° sites and the appearence of additional bands that can be assigned to N2O, NO, and carbonate species. These features indicate that NO is immediately dissociated on Ru already in the presence of preadsorbed CO and gives rise to N2O and CO2 already at RT. Upon heating at 373 K the N2O absorptions and the bands ascribed to CO adsorbed species are depleted and that of CO2 increases, indicating that the reaction 2CO+2NO→N2+2CO2 may prevail on the catalyst.

XPS surface study of nanocrystalline Ti–Ru–Fe materials

The surface properties of Ti:Ru:Fe (2−x:1+x/2:1+x/2) (with x=0, 0.25, 0.5, 0.75, and 1) and Ti:Ru:Fe:O (2:1:1:w) (with w=0.0, 0.5, 1.0, 1.5, and 2.0) have been determined by X-ray photoelectron spectroscopy (XPS) in both their as-milled state and after being in contact with a chlorate oxidizing solution. The O surface concentrations of both sets of samples are almost identical, indicating that the O-free samples readily react with air. All samples in their as-milled state have an elemental Ti, Ru and Fe surface contents that closely follow that expected from their bulk composition, indicating that there is no surface enrichment in any of the elements. In the as-milled state, more than 90% of Ti and Fe atoms are in the highest possible oxidation state, while Ru is in the metallic state. Following immersion of the samples in an oxidizing chlorate electrolyte, the Ru surface concentration decreases by a factor of two. This is also accompanied by an increase in the oxidation state of the Ru atoms left at the surface from 0 to +4. From a comparison between the Ru 3d5/2,3/2 core level spectra of the electrodes with those of crystalline and hydrated RuO2, it is postulated that dissolution and re-deposition of Ru in the form of hydrated RuO2 occurs at open circuit potential in the chlorate electrolyte. The consequences of these findings for the electrocatalytic activity of the electrodes in chlorate electrolyte are finally discussed.

Electrochemical surface reactions of intermediates formed in the oxidative ethanol adsorption on porous Pt and PtRu

The oxidative ethanol adsorption and electrochemical surface reactions of adsorbed intermediates were studied on electrodeposited Pt, Ru, Pt0.92Ru0.08 and Pt0.85Ru0.15 in 1 M HClO4. A flow cell procedure was performed in order to separate surface reactions of intermediates formed in the oxidative ethanol adsorption from those reactions for ethanol in the bulk electrolyte solution. Oxidation and reduction reactions of adsorbed species were studied by potential-controlled electrodesorption spectrometry. No adsorbate formation was observed on a pure Ru electrode. In all cases, CO2 was the sole product formed in the oxidative electrodesorption of the adsorbates. Using 12CH312CH2OH and 12CH313CH2OH, the oxidation reaction pathways of each C-atom to CO2 were followed. On the other hand, methane and ethane were detected during the reductive electrodesorption of adlayer species. The onset potential for these reduction products shifts to more negative potentials as the Ru content of the alloy increases. The methane to ethane yield ratio decreases in the sequence Pt>Pt0.92Ru0.08>Pt0.85Ru0.15. A critical interpretation of the experimental data leads to a tentative yield of different adsorbed species as function of the Ru surface concentration.

Fischer—Tropsch synthesis on alumina-supported ruthenium catalysts I. Influence of K and Cl modifiers

Fischer-Tropsch synthesis (FTS) has been studied at 5 · 10 3 Pa, at 508 K, an H 2/CO=2/1 molar ratio on Ru/γ-Al 2O 3 catalysts (1% Ru wt./wt.), using Ru(AcAc) 3 (AcAc standing for acetylacetonate), RuCl 3 and K(AcAc) as precursors; K/Ru and Cl/Ru molar ratios ranged from 0.14 to 2.18 and from 1.31 to 3.71, respectively. As Ru catalysts for FTS undergo easy alteration resulting from coke deposition, the results from kinetic runs were collected using both fresh catalysts (at 5–10 min time-on-stream) and also when steady state conditions were reached (about 150 min time-on-stream). The influence of K/Ru and Cl/Ru ratios on CO conversion and on the selectivity of the formation of different products in the reaction has been examined. Changes in activity, during the regeneration procedures of the catalysts, differ significantly when the precursor is Ru(AcAc) 3 (increase in activity after regeneration cycle) or RuCl 3 (significant deactivation with a decrease in Ru surface concentration, as determined by XPS).