Catalytic Performance Of Ru Research Articles

Lattice and Surface Engineering of Ruthenium Nanostructures for Enhanced Hydrogen Oxidation Catalysis

AbstractRu has recently been considered as a promising alternative of Pt toward hydrogen oxidation reaction (HOR) due to its lower price and similar hydrogen binding energy (HBE) in comparison to Pt. Nevertheless, the catalytic performance of Ru toward HOR is far from the satisfaction of practical application. Herein, it is demonstrated that the modification of Ru multi‐layered nanosheet (MLNS) with Ni can significantly promote the HOR performance. In particular, the HOR performance is strongly related to the Ni location on the surface or in the lattice of Ru MLNS. Experimental and theoretical investigations suggest that Ni in the lattice of Ru MLNS (lattice engineering) optimizes the HBE, while Ni species on the surface (surface engineering) decrease the free energy of water formation, as a result of the significantly enhanced HOR performance. The optimal catalyst, where Ni is located both on the surface and in the lattice, displays superior alkaline HOR performance to commercial Pt/C and Ru/C. The present study not only systematically reveals the significance of Ni modification on Ru toward HOR, but also promotes the fundamental researches on catalyst design for fuel cell reactions and beyond.

A Ruthenium(II) Water Oxidation Catalyst Containing a pH-Responsive Ligand Framework.

The synthesis of a new RuII-based water oxidation catalyst is presented, in which a nitrophenyl group is introduced into the backbone of dpp via a pH-sensitive imidazole bridge (dpp = 2,9-di-(2′-pyridyl)-1,10-phenanthroline). This modification had a pronounced effect on the photophysical properties and led to the appearance of a significant absorption band around 441 nm in the UV–vis spectrum upon formation of the monoprotonated species under neutral conditions. Theoretical investigations could show that the main contributions to this band arise from transitions involving the imidazole and nitrophenyl motif, allowing us to determine the pKa value (6.8 ± 0.1) of the corresponding, twofold protonated conjugated acid. In contrast, the influence of the nitrophenyl group on the electrochemical properties of the catalytic center was negligible. Likewise, the catalytic performance of Ru(dppip-NO2) and its parent complex Ru(dpp) was comparable over the entire investigated pH range (dppip-NO2 = 2-(4-nitrophenyl)-6,9-di(pyridin-2-yl)-1H-imidazo[4,5-f][1,10]phenanthroline). This allowed the original catalytic properties to be retained while additionally featuring a functionalized ligand scaffold, which provides further modification opportunities as well as the ability to report the pH of the catalytic solution via UV–vis spectroscopy.

Catalytic performance of Ru, Os, and Rh nanoparticles for ammonia synthesis: A density functional theory analysis

NH3 synthesis on Ru, Os, and Rh nanoparticle catalysts was investigated using density functional theory calculations. The Ru and Os nanoparticles exhibited similar shapes, while that of Rh differed significantly. For all metal species, step sites appeared at nanoparticle diameters (d) >2–4nm. The calculated activation barriers (Ea) were small at step sites, and Ru and Os step sites exhibited similar Ea values despite the former having a higher turnover frequency. This is likely due to the surface coverage of vacant sites being higher on Ru. Although the increase in NH3 synthesis rate at d = 2–4nm was common to Ru, Os, and Rh, the reaction rates decreased in the order: Ru > Os > Rh. Our results show that Ea values, surface vacant sites, and the number of step sites are important factors for NH3 synthesis. The Ru nanoparticles exhibited high activity due to satisfying all three factors.

Halloysite Nanotube Supported Ru Nanocatalysts Synthesized by the Inclusion of Preformed Ru Nanoparticles for Preferential Oxidation of CO in H2-Rich Atmosphere

The small-sized and well-dispersed Ru nanocatalysts supported on halloysite nanotubes (HNTs) were synthesized by the inclusion of preformed Ru nanoparticles onto HNTs (Ru NPs/HNTs) and employed for the preferential oxidation of CO in H2-rich atmosphere (PROX). Polyol reduction was adopted to prepare Ru nanoparticles, and the synthesis conditions affected the morphology of the resulting nanoparticles. The catalysis results show that the Ru NPs/HNTs present significantly higher CO conversion and CO2 selectivity than the catalyst prepared by traditional wet impregnation. RuCl3 is a better Ru precursor than Ru(acac)3 for synthesizing Ru nanoparticles with higher catalytic reactivity. The catalytic performance of Ru NPs/HNTs can be further enhanced by the reduction pretreatment due to the removal of polyvinylpyrrolidone (PVP) capping on the surface of Ru nanoparticles, and this enhancement is more significant with reduction at 400 °C than at 200 °C. Finally, the characterizations on the used catalysts indicate that the morphology of Ru nanoparticles is maintained after PROX reaction; slight growth of particle size is observed with 200 °C reduction pretreatment, yet Ru nanoparticles lose their original size and shape with 400 °C reduction.

Study on Effect Recyclability of Ru/Bentonite-TiO<sub>2</sub> Catalysts in Glycerol Hydrogenolysis Reaction Using X-Ray Photoelectron Spectroscopy (XPS)

Recyclability effect on catalytic performance of Ru supported on the mixture of bentonite-TiO2 for the hydrogenolysis of glycerol was investigated under reaction condition of 150°C, 2.0 MPa hydrogen pressure and 7 h reaction time. Interestingly, the recovered Ru/bentonite-TiO2 catalyst was found to be active in the repeated runs. The conversion of glycerol increased in the four successive reactions as follows: 61.3%, 65.6%, 68.1% and 75.3%. This suggested that a sort of metal activation affect such as in situ reduction occurred during the repeated reaction. In order to confirm in situ reduction had occurred during the repeated reaction, XPS analysis of used catalyst after each reaction were carried out to study the chemical state of Ru 3d species. Narrow scan of peak Ru 3d revealed that intensity of Ru 3d5/2 peak at BE 280.0 eV which is corresponding to Ru0 species increased until three cycle reaction. This result confirmed that in situ reduction had occurred during the repeated reaction and this made the activities of the catalyst increased upon recycling due to the availability of more metallic Ru on the surface of the catalyst. This study also shows that conversion of glycerol increased linearly with the percentage atomic ratio of Ru metal active site available on the surface of catalyst.

Influence of preparation method and boron addition on the metal function properties of RuSn catalysts for selective carbonyl hydrogenation

AbstractBACKGROUND: Improvements in the selective hydrogenation of unsaturated fatty acid methyl esters in order to obtain unsaturated fatty alcohols have been attempted through the preparation and modification of supported group VIII metallic catalysts. Suitable catalysts appear to be those based on supported Ru modified by Sn. The influence of preparation and activation methods on the structural and electronic properties of the metallic phase and the effect of modifications to these properties on the catalytic performance of RuSn/Al2O3 catalysts was studied regarding selective hydrogenation of carbonyl groups.RESULTS: Preparation methods have a marked influence on the electronic state of Ru and its interaction with Sn. Temperature‐programmed reduction (TPR), Fourier transform infrared spectroscopy of chemisorbed CO (FTIR‐CO) and X‐ray photoelectron spectroscopy (XPS) results clearly show that the incorporation of sodium borohydride in the preparation leads to a greater RuSn interaction when compared with catalysts prepared by co‐impregnation without B. The activation of catalysts without B (either by direct reduction or calcinations‐reduction) does not produce a strong RuSn interaction. B‐containing catalysts exhibit higher hydrogenolytic and lower dehydrogenating activities. Selectivity towards oleyl alcohol formation was 37% for this catalyst, while catalysts without B were not suitable for obtaining fatty alcohols.CONCLUSION: The degree of interaction between Ru and Sn strongly depends on catalyst preparation and activation method where strong interaction promotes selectivity with respect to oleyl alcohol formation. On the contrary, catalysts with a weak RuSn interaction do not show significant selectivity for the unsaturated alcohol. Copyright © 2010 Society of Chemical Industry

THE EFFECTS OF RARE EARTHS ON ACTIVITY AND SURFACE PROPERTIES OF Ru/γ-AL2O3 CATALYST FOR WATER GAS SHIFT REACTION

A series of Ru-RE/γ-AL2O3 (RE = Ce, Pr, La, Sm, Tb or Gd) and Ru/γ-AL2O3 catalysts were prepared by impregnation method. The influence of rare earths on the catalytic performance of Ru/γ-AL2O3 catalyst for the water gas shift reaction was studied. The catalysts were characterized by X-ray diffraction (XRD), temperature programmed reduction (TPR), temperature programmed desorption (TPD), and CO chemisorption. The results show that the addition of rare earths increases the catalytic activity of Ru based catalyst. Among these cerium is the most remarkably. The addition of cerium increases the active surface area, improves the dispersion of ruthenium, and weakens the interaction between ruthenium and the support. Cerium also affects the adsorption and reduction properties of Ru/γ-AL2O3 catalyst. KEY WORDS: Rare earths, Ruthenium-based catalyst, Water gas shift reaction Bull. Chem. Soc. Ethiop. 2007, 21(3), 389-395.