Modification of copper by redox reaction: location of Ru on Cu-Ru bimetallic catalysts

Raney copper catalysts were modified by addition of ruthenium by means of an oxido-re-duction reaction between copper surface and ruthenium chloride in aqueous solution. Energy dispersive spectroscopy fitted to a STEM unit allowed to conclude that the active sites for the selective conversion of glucitol into 1,4–3,6-dianhydroglucitol are composed of ruthenium and chlorine located on low coordinated copper atoms.     

Carbon monoxide hydrogenation over silica-supported ruthenium-copper bimetallic catalysts

The catalytic properties of a series of ruthenium-copper catalysts supported on silica were studied. It was found that while the amount of CO adsorbed at 273 K measured with the pulse-flow method is higher on the catalysts with a small concentration of copper than on the pure ruthenium catalyst, the yield of Ru⁺ secondary ions on fast atom bombardment of the catalyst surface with argon is suppressed by the addition of copper. The activity for CO disproportionate as well as CO hydrogenation were drastically reduced by the presence of copper. It is estimated that an ensemble of between 4 to 6 adjacent ruthenium atoms is required for CO disproportionation and one of between 9 to 13 adjacent ruthenium atoms is required for CO hydrogenation. Comparisons between the properties of the supported catalysts and those of single-crystal model catalysts were made.     

Role of the support and of the preparation method for copper-based catalysts in the 2-propanol decomposition

Pure copper oxide and mixed CuO/ZnO catalysts with different Cu:Zn atomic ratios were tested for the 2-propanol decomposition in order to investigate the nature of the active site and the role of the ZnO support. Fresh catalysts as well as catalysts oxidized in pure oxygen did not exhibit any catalytic activity below 373 K. When reduced either in pure hydrogen or in reaction mixture (helium plus alcohol) both copper oxide and mixed two-phase catalysts showed a dehydrogenating activity in the temperature range 323–423 K. The apparent activation energy for both reduced CuO and reduced CuO/ZnO catalysts was 60 ± 8 kJ mol^–1. The first order rate constants were found to be a linear function of the exposed zero-valent copper area. The comparison of Cu(0) turnover frequency in unsupported Cu(0) and in Cu(0)/ZnO samples did not show any synergic effect of the support. The role of the preparation method on the Cu(0) dispersion is also discussed.     

Recyclable Solid Ruthenium Catalysts Supported on Metal Oxides for the Addition of Carboxylic Acids to Terminal Alkynes

Ceria‐supported ruthenium catalysts (Ru/CeO₂) were found to be quite effective for the addition of various carboxylic acids to terminal alkynes, which gave the corresponding enol esters in moderate to high yields. The major products of the reaction were E‐isomers of anti‐Markovnikov adducts. Among the ceria‐supported ruthenium catalysts examined, those prepared using ruthenium precursors with chloride ligands showed high activities. The zirconia‐supported ruthenium catalyst (Ru/ZrO₂) showed activity comparable to that of the ceria‐supported catalyst. These catalysts were recyclable without a significant loss of activity, and the leaching of ruthenium species into the liquid phase was negligible after cooling the reaction mixture, which indicates marked superiority of the present solid oxide catalysts to conventional homogeneous catalysts.     

Bio <Emphasis Type="Italic">n</Emphasis>-Butanol Partial Oxidation to Butyraldehyde in Gas Phase on Supported Ru and Cu Catalysts

Abstract  

Ceria, titania, and zirconia supported ruthenium and copper catalysts were tested in the butyraldehyde production by gas phase n-butanol partial oxidation. These catalysts were characterized by means of N₂ adsorption–desorption isotherms, temperature-programmed reduction and X-ray photoelectron spectroscopy techniques. The activity tests were performed in a fixed bed reactor at 0.1 MPa and 623 K using air and n-butanol mixture as reactants (in stoichiometric proportion n-butanol/O₂) to generate butyraldehyde. For n-butanol partial oxidation, the ruthenium catalysts showed higher activity and stability than the copper ones. The n-butanol conversion was almost similar for all the ruthenium catalysts, but the different supports modified the metal dispersion and, as a result, the product distribution was modified. The catalysts supported on ZrO₂ and CeO₂ allowed the highest butyraldehyde yields. The copper doping of the ruthenium catalyst also improved the selectivity toward butyraldehyde.     

The effect of copper on the reaction of ethylene on silica-supported Ru-Cu catalysts as studied by13C NMR

The adsorption and reaction of ethylene on silica-supported bimetallic RuCu catalysts has been studied by solid state, highresolution¹³C NMR in order to elucidate the effect of copper on the catalytic behavior. Copper itself exhibits no inherent activity for the reaction of ethylene whereas Ru is highly active, producing dimeric products (butenes and butanes) and ethane. The ability to form dimeric products is not changed by the introduction of copper into the metal particles. However, the bimetallic catalysts have significantly less hydrogenation capabilities than the supported monometallic ruthenium catalyst. Since copper is known to populate low-coordination, defect-like lattice positions such as edges and corners, it is postulated that these sites play a crucial role in hydrogenation reactions.     

草酸酯催化加氢制备乙二醇研究进展

综述了近年来碳一合成路线中草酸酯催化加氢制备乙二醇的研究进展。分别介绍了以Ru等贵金属催化剂为主的液相均相加氢法和以铜基催化剂为主的非均相气相或液相加氢法,详细介绍了各类催化剂在草酸酯催化加氢方面的特点。并且就目前国内外对草酸酯氢化动力学方面的研究予以总结,给出了草酸酯加氢过程典型的动力学过程。最后比较了分别以草酸二甲酯和草酸二乙酯为原料路线的优缺点。     

Steam reforming of naphthalene as model biomass tar over iron-aluminum and iron-zirconium oxide catalyst catalysts

In this study the catalytic properties of iron-based mixed metal oxides such as iron-alumina (Fe-Al) and iron-zirconia (Fe-Zr) were investigated at 850 °C in a fixed bed reactor for the steam reforming of naphthalene as a model biomass tar compound. The effects of addition of copper species (CuO) to the iron-based mixed metal oxide catalysts were also examined. For Fe-Al catalysts, the catalytic activities for naphthalene conversion increased with increasing Fe content except for 100Fe-0Al. The catalytic activities of Fe-Al and Fe-Zr were comparable at steady state conditions. Compound oxides were formed in the cases of Fe-Al, but not in Fe-Zr. A strong peak in the vicinity of 2θ = 45° for metallic iron was observed after catalytic experiments in the XRD patterns of all catalysts, which could be related to the active sites of the catalysts. The addition of CuO increased the activities and stability of the Fe-Al catalysts. The reasons for catalytic activity enhancement due to CuO addition can be explained as follows: copper dispersed evenly in the compound oxides facilitate the reduction of iron oxides to metallic iron and prevent the catalytic deactivation due to decrease in surface area of the catalysts during the reaction.     

Ruthenium selenide catalysts for cathodic oxygen reduction in direct methanol fuel cells

The oxygen reduction reaction in sulphuric acid on commercial carbon supported platinum and ruthenium catalysts as well as on a home-made carbon supported ruthenium selenide catalysts (RuSe _x /C) was investigated. The RuSe _x /C catalysts were synthesised using similar procedures to those found in the literature. A dependency of H₂O₂ formation on the selenium content was found using the thin-film rotating ring disc electrode technique, namely that the H₂O₂ formation in the typical operation range of a Direct Methanol Fuel Cell (0.7–0.4 V) on Pt/C is below 1% and 1–4% on Ru/C and RuSe _x /C catalysts. Finally for comparing the intrinsic activities of the catalysts the electrochemically active surface areas were determined in-situ by means of copper underpotential deposition. Our results indicate a comparable activity of the present RuSe _x /C catalyst to commercial Pt/C if the activities are related to the electrochemical active areas.     

Partial oxidation of methane over ruthenium catalysts

The catalytic partial oxidation of methane with oxygen to produce synthesis gas was studied under a wide range of conditions over supported ruthenium catalysts. The microreador results demonstrated the high activity of ruthenium catalysts for this reaction. A catalyst having as little as 0.015% (w/w) Ru on Al₂O₃ gave a higher synthesis gas selectivity than a catalyst having 5% Ni on SiO₂. XANES measurements for fresh and used catalyst samples confirmed that ruthenium is reduced from ruthenium dioxide to ruthenium metal early during the experiments. Ruthenium metal is thus the active element for the methane partial oxidation reaction.     

Solid Phase Catalytic Ozonation Process for the Destruction of a Model Pollutant

Pure metal oxides, mixed metal oxides, and platinum metals were evaluated as ozonation catalysts. Batch reactor experiments were performed using deionized water at pH 7 and semi-continuous ozonation experiments were performed using a natural water. p-Chlorobenzoic acid (pCBA), a non-adsorbing model micropollutant that does not react directly with molecular ozone, was included in both solution matrixes. Titanium dioxide, cobalt oxide, nickel oxide, copper oxide, and a mixed metal oxide comprised of copper, zinc, and aluminum did not accelerate the removal pCBA in deionized water. However, cobalt oxide and the mixed metal oxide catalyst were effective at accelerating the removal of pCBA in a natural water matrix. The mixed metal oxide catalyst may have the most potential as an ozonation catalyst because it also was very stable (i.e., low solubility). A ruthenium / alumina catalyst also increased the removal of pCBA, but this metal may follow a different reaction mechanism than the metal oxide catalysts.     

The effect of Si/Al ratio and copper exchange level on isothermal kinetic rate oscillations for N2O decomposition over Cu-ZSM-5: a transient FTIR study

Kinetic rate oscillations in the decomposition of N₂O over Cu-ZSM-5 were studied over a series of catalysts with varying Si/Al ratios and copper exchange levels. Oscillations were observed to occur over all catalysts with Si/Al≥29 and exchange level >100%, including excessively-exchanged catalysts with Cu/Al>1.0. FTIR spectroscopy showed that the same monodentate nitrate species was present under reaction conditions for all catalysts displaying oscillatory behavior, and that the coverage of this species was correlated to the gas phase oscillations. Catalysts with low Si/Al ratios did not show oscillation due to a combination of factors: (1) additional actives sites exist on these catalysts (possibly Cu ion pairs) that stabilize additional nitrate species, (2) the nitrate species desorb at a lower temperature compared to the other zeolite catalysts, and (3) the formation of nitrate on these catalysts was shown to be an order of magnitude slower than on the catalysts which show oscillations. FTIR-based kinetic studies of nitrate formation verified that the most critical reaction occurs between N₂O and extra lattice oxygen in order to form NO, which is converted rapidly to surface nitrate. FTIR also identified a possible intermediate in the formation of nitrate at 1537 cm⁻¹ that has been assigned to monodentate nitrite on Cu²⁺ ions.     

NO decomposition and reduction by C3H6 over transition metal oxides supported on MgF2

The monooxides copper, manganese, molybdenum and chromium catalysts supported on MgF₂ were tested in NO decomposition and reduction by propene. The effect of the oxides content, time on stream and O₂ concentration in reaction mixture during NO reduction on their catalytic activity was investigated. All the catalysts showed the optimum active phase concentration corresponding to 2–4 wt.% of the metal. For the best copper catalyst an effect of introduction of another oxide (manganese or chromium oxide) on the catalytic performance was studied. The double copper-manganese oxide sample containing 2 wt.% Cu and 4 wt.% Mn was proved to ensure the best catalytic performance.     

钌催化剂上苯加氢制环己烯的影响因素

综述了钌催化剂上苯选择性加氢的反应机理、催化剂制备过程中前躯体、制备方法、载体、添加剂(水,有机添加剂,无机添加剂)对催化剂催化性能的影响和反应过程中温度、压力、搅拌速率、催化剂用量及反应时间等对苯转化率、环己烯选择性和环己烯收率的影响。     

Insights into Supported Copper(II)‐Catalyzed Azide‐Alkyne Cycloaddition in Water

Cross‐linked polymeric ionic liquid material‐supported copper (Cu‐CPSIL), imidazolium‐loaded Merrifield resin‐supported copper (Cu‐PSIL) and silica dispersed CuO (CuO/SiO₂), were prepared and proved to be efficient catalysts for the one‐pot synthesis of 1,4‐disubsituted‐1,2,3‐triazoles by the reaction of alkyl halides with sodium azide and terminal alkynes in water at room temperature. Moreover, these supported copper catalysts were recovered quantitatively from the reaction mixture by simple filtration and reused for five consecutive recycles without significant loss of catalytic activity. Among the three immobilized copper catalysts, Cu‐CPSIL exhibited excellent catalytic activity for the reaction of aliphatic bromides, sodium azide and terminal alkynes. The differences in the catalytic performances of the catalysts could be ascribed to the copper dispersion and the interaction between copper and the supports. In addition, water was used as the reaction media and the proton provider, the latter was found to be very important for the reaction. The XPS results suggested that the supported Cu(II) catalysts were reduced to catalytic Cu(I) species via alkynes homocoupling reaction. By means of IR and ESI‐MS studies, a possible mechanism of cycloaddition based on the reduction of Cu(II) to Cu(I) species was proposed.     

Metalloporphyrins as catalysts in the decomposition of cyclohexyl hydroperoxide

A series of metalloporphyrins with various metals were tested as catalysts in the decomposition of cyclohexyl hydroperoxide. The more active complexes are those of manganese(III), iron(III), chromium(III) and ruthenium(II). No relation could be found between the redox potentials of the catalysts and their activity.This work is part of the thesis by C.B. Hansen, Utrecht, 1991.     

Surface characterization of palladium-copper bimetallic catalysts by FTIR spectroscopy and test reactions

Different bi-metallic palladium-copper catalysts have been prepared according to different sequences of impregnation of a commercial alumina. CO adsorption followed by FTIR spectroscopy was performed in order to identify the nature of the superficial sites. Two test reactions were also used to characterize the nature of the active surface site: gas phase toluene hydrogenation was selected in order to show the hydrogenating activity of metallic palladium, whereas the reaction of decomposition of ethanol, which exhibits 100% selectivity in the formation of ethanal on pure copper catalysts, was also studied on this series of catalysts. The results obtained by both methods are complementary. By comparison with the behaviour of pure palladium or copper based catalysts, they allow to propose hypotheses on the surface composition: separated phases, alloys or a phase covered by the other one.     

钌基催化剂在加氢反应中的应用

钌基催化剂在低温和低压等温和条件下具有优异的催化性能,因而广泛应用于各种反应中。文章介绍了钌基催化剂的研究现状,着重探讨了其在加氢反应中的应用和研究进展,包括载体材料、前驱体和助剂对催化剂性能的影响。所涉及的反应包括:CO2加氢合成甲酸、CO/CO2甲烷化、苯加氢制环己烯、苯胺加氢制环己胺与二环己胺、多元醇加氢制备二元醇、葡萄糖加氢合成山梨醇等,并对它的应用前景进行了展望。     

Influence of Ru precursor,support and solvent in the hydrogenation of citral over ruthenium catalysts

A series of ruthenium supported catalysts were prepared and investigated in the liquid-phase hydrogenation of citral. The mechanism of the reaction was found to be dependent on the Ru precursor, support and solvent used. On the sample prepared from RuCl₃ the acetals of citronellal were formed with the subsequent hydrogenation of the isolated C=C double bond. On the samples obtained from precursors which do not contain chloride ions, citronellal was the main reaction product. Hydrogenation of the isolated C=C double bond was negligible. Using cyclohexane as solvent, a large amount of isopulegol was also obtained. The results of the hydrogenation of citral have been correlated to the presence of acid sites and incompletely reduced ruthenium which favour cyclization and acetals formation from citronellal. On the basis of the reported results, a reaction scheme for hydrogenation of citral over ruthenium catalysts is proposed.     

Selective Hydrogenation of 5‐Ethoxymethylfurfural over Alumina‐Supported Heterogeneous Catalysts

We report here the synthesis and testing of a set of 48 alumina‐supported catalysts for hydrogenation of 5‐ethoxymethylfurfural. This catalytic reaction is very important in the context of converting biomass to biofuels. The catalysts are composed of one main metal (gold, copper, iridium, nickel, palladium, platinum, rhodium, ruthenium) and one promoter metal (bismuth, chromium, iron, sodium, tin, tungsten). Using a 16‐parallel trickle‐flow reactor, we tested all 48 catalyst combinations under a variety of conditions. The results show that both substrate conversion and product selectivity are sensitive towards temperature changes and solvent effects. The best results of >99% yield to the desired product, 5‐ethoxymethylfurfuryl alcohol, are obtained using an iridium/chromium (Ir/Cr) catalyst. The mechanistic implications of different possible reaction pathways in this complex hydrogenation system are discussed.