Silica-supported Ru Research Articles

Engineering ZrO2–Ru interface to boost Fischer-Tropsch synthesis to olefins

Understanding the structures and reaction mechanisms of interfacial active sites in the Fisher-Tropsch synthesis reaction is highly desirable but challenging. Herein, we show that the ZrO2-Ru interface could be engineered by loading the ZrO2 promoter onto silica-supported Ru nanoparticles (ZrRu/SiO2), achieving 7.6 times higher intrinsic activity and ~45% reduction in the apparent activation energy compared with the unpromoted Ru/SiO2 catalyst. Various characterizations and theoretical calculations reveal that the highly dispersed ZrO2 promoter strongly binds the Ru nanoparticles to form the Zr-O-Ru interfacial structure, which strengthens the hydrogen spillover effect and serves as a reservoir for active H species by forming Zr-OH* species. In particular, the formation of the Zr-O-Ru interface and presence of the hydroxyl species alter the H-assisted CO dissociation route from the formyl (HCO*) pathway to the hydroxy-methylidyne (COH*) pathway, significantly lowering the energy barrier of rate-limiting CO dissociation step and greatly increasing the reactivity. This investigation deepens our understanding of the metal-promoter interaction, and provides an effective strategy to design efficient industrial Fisher-Tropsch synthesis catalysts.

Efficient hydrogenolysis of cellulose into sorbitol catalyzed by a bifunctional catalyst

A sulfonic acid-functionalized silica-supported ruthenium catalyst (Ru/SiO2–SO3H) was employed for the hydrogenolysis of cellulose in one pot in neutral water medium. Ru/SiO2–SO3H is a bifunctional catalyst containing both a Brønsted acidic site and a metal site (Ru). Compared with the mechanical mixture of a silica-supported Brønsted acid (SiO2–SO3H) and a silica-supported Ru catalyst (Ru/SiO2), the bifunctional catalyst showed much higher yield of sorbitol, which could reach up to 61.2% when the reaction was performed for 10 h at 150 °C. Through the characterization by XPS and pyridine-adsorbed FT-IR, the existence of the interaction between sulfonic groups and Ru nanoparticles in the Ru/SiO2–SO3H catalyst was observed. The sulfonic acid groups and metal sites in the adjacent position were important for enhancing the yield of sorbitol. In addition, the present catalyst can be reused five times with only a slight decrease in yield of sorbitol in the consecutive recycles.

ChemInform Abstract: Pretreatment Chemistry in the Preparation of Silica-Supported Pt, Ru, and Pt-Ru Catalysts: An in situ UV Diffuse Reflectance Study.

ChemInform Abstract: Pretreatment Chemistry in the Preparation of Silica-Supported Pt, Ru, and Pt-Ru Catalysts: An in situ UV Diffuse Reflectance Study.

ChemInform Abstract: The Effect of Chlorine on Hydrogen Chemisorption by Silica-Supported Ru Catalysts: A Proton NMR Study.

Silica-supported ruthenium catalysts prepared from the RuCl3 · 3H2O precursor contain residual chloride after reduction in flowing hydrogen. The amount of this chlorine was determined by X-ray fluorescence spectroscopy to be less than one monolayer on the ruthenium surfaces. Both volumetric hydrogen chemisorption and proton NMR show suppression of hydrogen chemisorption capacity associated with the presence of chlorine contamination, which can be removed effectively with hot water elution. The variations of the hydrogen chemisorption capacity with chlorine coverage suggests that chlorine would completely block and poison the Ru surfaces for hydrogen chemisorption at a Cl coverage of about 76%. The effect of residual chloride on the proton NMR resonance position and the spin-lattice relaxation time for the chemisorbed hydrogen indicates an electronic interaction between Cl adspecies and surface Ru, which results in the weakening of the H-Rus chemisorptive bond at the Ru surfaces. This reduced H-Rus interaction may be the cause for an increase in the ratio of the reversibly adsorbed hydrogen over the irreversibly adsorbed hydrogen with increasing Cl coverage. It is proposed that the mechanism for suppression of hydrogen chemisorption by chlorine involves both physical site blocking of surface Ru atoms and shortranged electronic interactions between Cl adatoms and neighboring surface Ru atoms.

Metal Particle Growth during Glucose Hydrogenation over Ru/SiO2 Evaluated by X-ray Absorption Spectroscopy and Electron Microscopy

Biorenewable resources such as carbohydrates are considered alternative feedstocks for oxygenated chemicals. This work investigates the stability of silica-supported Ru catalysts in the aqueous phase conversion of glucose to sorbitol. In situ X-ray absorption spectroscopy at the Ru K edge revealed that air-exposed silica-supported Ru was in an oxidized state but was subsequently reduced in aqueous solutions saturated with 40 bar H(2) at 373 K. Furthermore, exposure to aqueous phase conditions resulted in the sintering of Ru particles on the silica surface. However, the presence of glucose in the aqueous phase stabilized the growth of the Ru particles. Batchwise hydrogenation of glucose at 373 K and 80 bar H(2) over a Ru/SiO(2) (2.67 wt %) catalyst is nearly 100% selective to sugar alcohol with an average turnover frequency of 0.21 +/- 0.04 s(-1). The hydrogenation reaction was not mass transfer limited according to the Madon-Boudart criterion.

Hydrodechlorination of 1,1,2-trichloro-1,2,2-trifluoroethane (CFC-113) over supported ruthenium and other noble metal catalysts

The hydrodechlorination of CCl2F–CClF2 (CFC-113) was studied using silica- and activated carbon-supported Ru, Rh, Pd, and Pt catalysts. The activity of the catalysts changed with time-on-stream. Ru was most stable among the four noble metals and gave a simple product distribution yielding CClFCF2 (CFC-1113) and CHClF–CClF2 (HCFC-123a) as main products. Over silica-supported Ru, CFC-1113 yield decreased gradually with time-on-stream but HCFC-123a yield did not change throughout the reaction, suggesting that these products were formed on different sites of Ru. XRD studies and temperature-programmed reduction of the spent catalyst revealed that the deactivation was caused by halogen-containing carbonaceous species accumulated on the Ru surface during the reaction. The carbonaceous species seemed to be formed on the active site for CFC-1113 formation. Because CFC-1113 selectivity was higher over the catalyst having higher Ru dispersion, it was assumed that the hydrodechlorination of CFC-113 is structure-sensitive and CFC-1113 formation is promoted by Ru having highly unsaturated coordination sphere.

An infrared study of CO adsorption on silica-supported Ru–Sn catalysts

CO adsorption on Ru–Sn/SiO2 catalysts of various Sn/(Ru+Sn) ratios was examined by Diffuse Reflectance Infrared Fourier-Transform Spectroscopy (DRIFTS). The catalysts were prepared by the incipient wetness impregnation method. Catalysts were activated by H2 reduction at 773 K. CO adsorbed on the catalysts shows spectra whose band frequencies are divided into three groups: (i) High Frequency Region (HFR), containing a band at 2065 cm−1, (ii) Low Frequency Region 1 (LFR1), containing bands at 2040–2015 cm−1, (iii) Low Frequency Region 2 (LFR2), containing bands at 1990 and 1945 cm−1. The types of adsorbed CO species formed strongly depend on the ratio Sn/(Ru+Sn) in the catalyst, CO pressure and temperature of adsorption. Adsorption of CO on Ru sites in the Ru/SiO2 catalyst results in LFR1 bands at 2040–2015 cm−1, which are independent of the CO pressure but the adsorption complexes are easily destroyed by raising the temperature. The addition of Sn to the catalyst creates new sites for CO adsorption. After adsorption at 298 K, the HFR band at 2065 cm−1 and LFR2 bands at 1990–1950 cm−1 are observed. The relative intensities of these bands increase with increasing Sn-content in the samples. The LFR bands are thermally stable while the HFR band is not. The formation of the corresponding species is favored by increasing the CO pressure. Adsorbed CO species giving LFR1 bands are assigned to linearly-adsorbed CO on the Ru0 and/or on the Ru–Sn alloy sites. Adsorbed CO species giving HFR bands are assigned to CO adsorption on Ruδ+–O–Sn sites. After low temperature CO adsorption on samples with high Sn-content, only species that show bands at 1990 and 1945 cm−1 in LFR2 are observed.

A comparison between silica-immobilized ruthenium(II) single sites and silica-supported ruthenium nanoparticles in the catalytic hydrogenation of model hetero- and polyaromatics contained in raw oil materials

A comparative study of the hydrogenation of various heterocycles, model compounds in raw oil materials, by either Ru(II) complex immobilized on mesoporous silica or Ru(0) nanoparticles deposited on the same support has been performed. The single-site catalyst contains the molecular precursor [Ru(NCMe) 3(sulphos)](OSO 2CF 3) tethered to partially dehydroxylated high-surface-area silica through hydrogen bonds between silanol groups of the support and SO 3 − groups from both the sulphos ligand [ −O 3S(C 6H 4)CH 2C(CH 2PPh 2) 3] and the triflate counter anion. Highly dispersed ruthenium nanoparticles were prepared by calcination/reduction of silica-supported Ru 3(CO) 12. The heterocycles (benzo[ b]thiophene, quinoline, indole, acridine) are hydrogenated to cyclic thioethers or amines. The Ru(II) single-site catalyst is active for both benzo[ b]thiophene and the N-heterocycles, while the Ru(0) catalyst does not hydrogenate the S-heterocycle, yet is efficient for the reduction of the N-heterocycles and simple aromatic hydrocarbons. The surface silanols promote the hydrogenation of indole via NH⋯ O(H)Si hydrogen bonds and can interact with the π-electron density of all substrates.

Microcalorimetric, infrared spectroscopic and DFT studies of ethylene adsorption on Ru, Ru/Sn and Ru/Cu catalysts

Microcalorimetric measurements of the adsorption of H2, CO and C2H4 were conducted on silica-supported Ru, Ru/Sn, Ru/Cu and Cu catalysts; infrared spectroscopic measurements were made of adsorbed CO and C2H4. The adsorption of C2H4 leads to formation of di-σ-adsorbed ethylene and ethylidyne species on Ru/SiO2 at 300 K, with an initial heat of 160 kJ/mol. Ethylene adsorption at 203 K leads to the formation of di-σ-adsorbed ethylene, ethylidyne species and weakly adsorbed π-bonded ethylene. The initial heats are 110, 95 and 75 kJ/mol on Ru/SiO2, 5Ru/Sn/SiO2 and Ru/Cu/SiO2, respectively. Lower heats of CO and C2H4 adsorption are measured on Ru/Cu/SiO2, primarily as a result of these adsorbates binding on both Cu and Ru. Quantum chemical calculations employing density functional theory were performed using (0001) slabs of Ru and Ru/Sn. The results of these calculations indicate that Sn weakens the interaction of π-bonded ethylene, di-σ-bonded ethylene and ethylidyne species with Ru by 41, 23 and 15 kJ/mol, respectively. This behavior is in contrast to the effect of adding Sn to Pt and Pd, for which Sn preferentially weakens the bonding of ethylidyne species to the surface.

Methane conversion by various metal, metal oxide and metal carbide catalysts

The progress in the field of methane conversion into higher hydrocarbons including aromatics and oxygenated compounds in the recent five years will be reviewed shortly, together with a new type of the methane conversion reaction with carbon monoxide at lower temperatures (600–700 K) by supported group VIII metal catalysts. Benzene was formed selectively among hydrocarbons in the CH4–CO reaction over silica-supported Rh, Ru, Pd and Os catalysts under atmospheric pressure. Both CH4 and CO were required for benzene formation, and only ethane and ethylene were formed besides benzene. The amount of C3–C5 hydrocarbons was negligible, which suggests that a completely different mechanism from the CO–H2 reaction may be operating over these catalysts despite of the similarity in the reaction conditions with the CO–H2 reaction. The mechanism of benzene formation was studied deeply by means of kinetical investigation as well as infrared spectroscopy and isotopic tracer method in connection with that of CO hydrogenation.

Hydrogen adsorption states on silica-supported Ru–Ag and Ru–Cu bimetallic catalysts investigated via microcalorimetry

The nature of hydrogen adsorption states on silica supported Ru, Ru–Ag and Ru–Cu was investigated using microcalorimetry and selective hydrogen chemisorption. The differential heats of hydrogen adsorption as a function of hydrogen coverage were determined for Ru and bimetallics with varying Ag and Cu contents. The initial heats of hydrogen adsorption (differential heat at coverages approaching zero) were found to be similar on all three catalyst systems suggesting the absence of effects that directly alter the chemisorptive bond (e.g. electron transfer between Ru and the added metal). The addition Ag to Ru significantly reduced the total amount of hydrogen adsorbed per surface Ru atom. That is, the stoichiometry of adsorption was altered by the addition of Ag even though Ag does not adsorb hydrogen. Similarly, the addition of Cu reduced the amount of hydrogen adsorbed per surface metal atom. In both cases, the reduced amount of hydrogen adsorbed per surface atom (adsorptive stoichiometry) was associated with the loss of hydrogen adsorbed from weak and intermediate energy adsorption states (<80 kJ/mol). The population of sites with adsorption energies ≥80 kJ/mol were unaffected. From atomistic simulations it is known that, at low concentrations, Ag and Cu preferentially occupy the low coordination metal sites. The loss of the intermediate and low adsorption energy sites is correlated with replacement of Ru atoms at edge, corner and other defectlike sites by Ag and Cu. Possible reasons for this structure sensitivity are discussed.

Methane Activation and Conversion to Higher Hydrocarbons on Supported Ruthenium

The interaction of methane with silica-supported Ru has been investigated. Methane is found to undergo dissociative adsorption above 373 K. The prexponential factor for dissociative adsorption is 2.0×10−7–5.7×10−7and the activation energy is 5.9–7.0 kcal/mol. Three types of carbon are formed, designated as Cα, Cβ, and Cγ. The distribution among these species is dependent on the total carbon coverage and the length of time that the carbon has been aged at given temperature after deposition. Aging results in the conversion of Cβto Cα. The apparent activation energy for this process is 22 kcal/mol. Hydrogenation of the carbonaceous deposit produces methane and smaller quantities of ethane and propane. The distribution among these products depends on the surface coverage of carbon and the temperature of hydrogenation. Both the distribution of carbonaceous species present on the catalyst surface after dissociative adsorption of CH4and the distribution of alkanes formed upon isothermal hydrogenation of the carbonaceous deposit depend on whether or not the catalyst has been carburized.

Direct conversion of methane to higher hydrocarbons via an oxygen free, low-temperature route

The direct conversion of methane to higher hydrocarbons over a silica-supported Ru catalyst has been investigated via an oxygen free, two-step route. The reaction consists of decomposition of methane over a 3% silica-supp orted Ru catalyst at temperatures\((T_{CH_4 } )\) between 400 and 800 K to produce surface carbonaceous species followed by rehydrogenation of these species to higher hydrocarbons at\(T_{H_2 } \) of 368 K. It was found that the Ru/SiO2 catalyst exhibits a trend similar to that for single-crystal Ru catalysts. However, the temperature at which a maximum in ethane selectivity occurs shifts toward a higher temperature. It was also found that the ethane yield can be optimized by changing the surface carbon coverage. Under optimum conditions a net ethane yield of about 13–15% has been realized. For this two-step reaction sequence, only a few reaction cycles could be operated without intermediate high temperature rehydrogenation and without significant loss in ethane yield. This is attributed to large amounts of inactive carbon that could not be hydrogenated at 368 K. Higher methane partial pressures were found to be desirable for this reaction. The activity of the catalyst could also be maintained at total pressures up to 10 atm.

The effect of chlorine on hydrogen chemisorption by silica-supported Ru catalysts: A proton NMR study

Silica-supported ruthenium catalysts prepared from the RuCl 3 · 3H 2O precursor contain residual chloride after reduction in flowing hydrogen. The amount of this chlorine was determined by X-ray fluorescence spectroscopy to be less than one monolayer on the ruthenium surfaces. Both volumetric hydrogen chemisorption and proton NMR show suppression of hydrogen chemisorption capacity associated with the presence of chlorine contamination, which can be removed effectively with hot water elution. The variations of the hydrogen chemisorption capacity with chlorine coverage suggests that chlorine would completely block and poison the Ru surfaces for hydrogen chemisorption at a Cl coverage of about 76%. The effect of residual chloride on the proton NMR resonance position and the spin-lattice relaxation time for the chemisorbed hydrogen indicates an electronic interaction between Cl adspecies and surface Ru, which results in the weakening of the H-Ru s chemisorptive bond at the Ru surfaces. This reduced H-Ru s interaction may be the cause for an increase in the ratio of the reversibly adsorbed hydrogen over the irreversibly adsorbed hydrogen with increasing Cl coverage. It is proposed that the mechanism for suppression of hydrogen chemisorption by chlorine involves both physical site blocking of surface Ru atoms and shortranged electronic interactions between Cl adatoms and neighboring surface Ru atoms.

Ethene hydrogenation over silica-supported Ru and Ru-Cu bimetallic catalysts: the role of defects and special sites

1H NMR of chemisorbed hydrogen and solid state 13C NMR were used to investigate ethene hydrogenation and decomposition on Ru/SiO 2 and Ru-Cu/SiO 2 catalysts. 1H NMR results on Ru/SiO 2 catalysts indicate that the weakly adsorbed hydrogen is more concentrated on defect-like Ru sites, and it is suggested to be thermodynamically more accessible than strongly adsorbed hydrogen for ethene hydrogenation under typical reaction conditions. Results from 1H NMR also indicate that addition of Cu reduces the amount of the weakly bound hydrogen. Addition of Cu to Ru/SiO 2 catalysts suppresses the activity of ethene hydrogenation as observed by 13C NMR. This effect may be due to preferential population of defect-like edge and corner Ru sites by Cu, subsequently limiting the amount of the weakly bound hydrogen on the metal surfaces necessary for ethene hydrogenation.

The effect of chlorine modification of silica-supported Ru on its CO hydrogenation properties

An investigation of CO hydrogenation on Cl-modified supported Ru catalysts has been carried out using both steady-state Fischer-Tropsch synthesis and steady-state isotopic transient kinetic analysis of methanation. The steady-state reaction results illustrate how the presence of chlorine acts to decrease catalytic activity and to enhance the selectivity of methane formation even though it is present on the catalyst only during the initial stages of the reaction. The deactivation results for F-T as well as the isotopic transient results suggest that structural rearrangements induced by the presence of chlorine, rather than selective site blocking or electronic interactions, may be the primary mechanism of chlorine modification of the catalytic properties of supported ruthenium for CO hydrogenation. Isotopic transients indicated that the decrease in methanation activity with increasing initial Cl concentration was a function of a decrease in the number of reactive surface intermediates (or sites) and not of a change in site activity.

Characterization of silica-supported RuAg and RuAu bimetallic catalysts by hydrogen chemisorption and nmr of adsorbed hydrogen

Silica-supported RuAg and RuAu bimetallic catalysts were studied by hydrogen chemisorption and by nuclear magnetic resonance (NMR) of adsorbed hydrogen. Both techniques yielded nearly the same capacity for hydrogen chemisorption on both series of bimetallic catalysts. A small difference measured by the two techniques was attributed to hydrogen spillover from ruthenium onto the silica support. This effect of hydrogen spillover was less pronounced in RuAg/SiO 2 than in RuAu/SiO 2, as indicated by the longer spin-lattice relaxation times of the silanol proton. The results of these studies are used to infer that a stronger interaction exists between silver and ruthenium than between gold and ruthenium in the supported bimetallics. Both NMR results and volumetric chemisorption results show that residual chlorine inhibits the hydrogen chemisorption capacity of the Ru/SiO 2 catalyst and RuAu/SiO 2, bimetallic catalysts. The variation of the adsorbed hydrogen chemical shift with chlorine coverage indicates an electronic interaction that is due to chlorine adsorption. A direct comparison between clean RuCu/SiO 2 (from a previous study), RuAg/SiO 2, and Ru-Au/SiO 2, bimetallic catalysts was made to illustrate the varying degrees of interaction between ruthenium and copper, silver, or gold.

13C High resolution NMR studies of adsorption and reaction of ethylene on silica-supported Ru and RuCu catalysts

The adsorption and subsequent reaction of ethylene on silica-supported Ru and RuCu bimetallic catalysts have been studied via nuclear magnetic resonance (NMR) employing a variety of experimental nuclear spin dynamics. NMR of 13C using cross polarization (CP) and magic angle spinning (MAS) allowed us to simultaneously observe transformations of chemisorbed species and weakly adsorbed molecules. Direct 13C excitation allowed quantitative measurements of various species on the surface. At room temperature the ethylene adsorbed on the ruthenium catalysts rapidly and converted to strongly adsorbed acetylide and alkyl species. Weakly adsorbed ethane, butane and cis- and trans-2-butene were observed. The butene slowly hydrogenated to form additional butane. When the temperature was raised to 140°C propane and methane were observed suggesting hydrogenolysis of the product molecules. The introduction of copper into the catalysts reduced the hydrogenation capability while still maintaining the ability to form dimeric products. In addition to butene and butane, butadiene was observed on the bimetallic catalysts.

Ultrahigh vacuum temperature-programmed desorption of CO and D 2 from silica-supported ruthenium: Evidence for spillover of D 2

The ultrahigh vacuum temperature-programmed desorption of D 2 and CO from silica-supported Ru was studied. Features attributed to D 2 spillover were observed for doses at temperatures above 323 K. The CO desorption spectra were broad and indicated a very heterogeneous distribution of adsorption sites but no spillover. The desorption of predosed D 2 from coadsorbed D 2 + CO showed that CO displaces weakly bound D(a) causing the D 2 desorption peak to shift to higher temperatures. Preadsorbed D(a) caused no changes in the desorption of CO. A small amount of CD 4 desorbed when CO and D were coadsorbed. The potential catalytic role of the spillover D(a) is discussed.

An IR investigation of CO chemisorbed on ruthenium microcrystals supported on silica

The IR spectra of CO adsorbed on silica-supported Ru in highly dispersed and sintered form have been measured and compared with the spectra obtained on flat and stepped faces of single crystals. Sintered Ru particles show hexagonal shape with predominance of the {001} facelets: this fact explains the similarity between the spectrum of CO adsorbed on them and on {001} single crystal faces. Due to the presence of well shape crystallites, sintered samples are suitable for spectroscopic investigations concerning adsorbate-adsorbate interactions of dynamic and static type. The separation between the dynamic and static contributions has been made by using isotopic 12CO 13CO mixtures.