Thermal stability of Ag–Au,Cu–Au,and Ag–Cu bimetallic nanoparticles supported on highly oriented pyrolytic graphite

The formation of Ag–Au, Cu–Au, and Ag–Cu bimetallic particles on the surface of highly oriented pyrolytic graphite was studied by X-ray photoelectron spectroscopy. Samples with the core–shell structure of particles were prepared by sequential thermal vacuum deposition. The thermal stability of the samples was studied over a wide range of temperatures (25-400°C) under ultrahigh-vacuum conditions. The heating of the samples to ~250°C leads to the formation of bimetallic alloy particles with a relatively uniform distribution of metals in the bulk. The thermal stability of the samples with respect to sintering depends on the nature of the supported metals. Thus, the Ag–Au particles exhibited the highest thermal resistance (~350°C) under ultrahigh-vacuum conditions, whereas the Ag–Cu particles agglomerated even at ~250°C.     

Effects of glow discharge plasma on Cu–Co–Al-based supported catalysts for higher alcohol synthesis

The novel plasma assisted Cu–Co/γ-Al₂O₃ catalysts were prepared by incipient impregnation method for CO hydrogenation to higher alcohols and characterized by means of scanning electron microscopy (SEM), N₂ adsorption, X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques. It was found that introduction of plasma significantly improved the specific surface area, dispersion of catalyst and the enrichment of active species on the surface of catalysts. Under the conditions of P = 5.0 MPa, GHSV = 6,000 h⁻¹, V(H₂)/V(CO) = 2, T = 573 K, the conversion of carbon monoxide over the plasma enhanced catalyst increased by 41.9% compared with that of the conventional sample, and the space time yield reached 337.1 g kg⁻¹ h⁻¹.     

Catalytic synthesis of isoprenol from fatty acid ester over bimetallic Cu–Fe catalysts

Supported bimetallic Cu–Fe catalysts revealed high activity and selectivity in isoprenyl acetate hydrogenation to isoprenol under mild reaction conditions (2 MPa H₂ and 170 °C). The nature of the carrier has a significant impact on the catalytic properties of Cu–Fe catalysts. The best catalytic properties were found for the 5% Cu–5% Fe/Al₂O₃ bimetallic catalyst, which provides a 98% isoprenyl acetate conversion in 4 h with the isoprenol selectivity of 82%.     

Steam reforming of methanol over mesoporous Cu–Al spinel catalysts synthesized by mechanochemical method

Hydrogen production for fuel cells via on-board steam reforming of methanol is a promising approach. In this study, an ammonium carbonate-assisted mechanochemical procedure has been developed for Cu-based catalyst synthesis for SRM. Catalytic performance in SRM was evaluated in a fixed bed reactor at varied conditions, and physical and structure properties of the catalysts were characterized by N₂ adsorption-desorption, N₂O titration, SEM, H₂-TPR, XRD and TG, etc. Mechanical milled samples exhibited a porous structure that differed from that of the catalyst prepared by conventional impregnation. The SRM activity was enhanced for the strong interaction between copper ions and the copper aluminate formed on the ball-milled catalysts. Cu₁Zn₃Al₆ exhibited the worst in activity, which could be ascribed to the poor metal dispersion. Cu–Al spinel in the catalysts plays an important role in the catalytic stability, which has prevented Cu from quick sintering in SRM, and the ball-milled catalysts have exhibited a slight deactivation with the time-on-stream of 25 ?h.     

Total oxidation of ethanol and toluene over ceria—zirconia supported platinum catalysts

The effect of platinum loading (0.09–1.00 mass %) on the performance of ceria-zirconia supported catalysts in the total oxidation of ethanol and toluene in air was investigated. The introduction of platinum promoted the reduction of surface cerium and decreased the acidity of the catalysts. In ethanol oxidation, the temperature of 50 % conversion decreased with increasing platinum content. This increase in catalytic performance was more pronounced for the catalysts with 0.59 mass % and 1.00 mass % Pt. On the other hand, higher amount of by-products (mainly acetaldehyde) was observed at increased platinum loadings. For all catalysts, a correlation between their H₂-TPR profiles and catalytic performance was revealed. In toluene oxidation, only the catalysts with 0.59 mass % and 1.00 mass % Pt exhibited a lower temperature of 50 % conversion than pristine ceria-zirconia. The effect of platinum loading was less pronounced than in ethanol oxidation and a correlation between reduction behaviour and catalytic performance was not observed. The superior catalytic performance of the catalysts with 0.59 mass % and 1.00 mass % of Pt in both ethanol and toluene oxidation was ascribed to the presence of large platinum nanoparticles, which were not observed at lower Pt loadings.     

Solvent-free synthesis of alumina supported cobalt catalysts for Fischer–Tropsch synthesis

A novel mechano-synthesis method has been elaborated in this work for the design of efficient cobaltbased Fischer–Tropsch catalysts. The process aims to reduce the total number of steps involved in the synthesis of solid catalysts and thus to avoid relevant toxic solutions generated during the catalyst preparation. The mechano-synthesis of the Co/Al_2O_3 catalyst was processed in a low-energy vibratory micro mill and high energy planetary ball mill. Porous spherical γ-aluminas(1860 μm and 71 μm mean particle diameter) were used in this work as host compounds. Co_3O_4(3 μm mean particle diameter) has provided guest particles for mechano-synthesis. The catalysts were characterized by textural(surface area, porosity and particle size) and structural analyses(X-ray diffraction, TPR, SEM-EDX and microprobe). The microprobe images show deposition of Co_3O_4 on the surface of the alumina and indicated no Co_3O_4 diffusion inside the alumina pores. SEM-EDX mapping illustrated that cobalt coating tended to occur on surface of rounded shape of cracked alumina fragments. After milling, the crystallite size of Co_3O_4 decreased to 15 nm from 30 to 50 nm. The TPR profiles indicated very low concentrations of inactive cobalt aluminate mixed compounds which are usually produced during the catalyst preparation by impregnation.In Fischer–Tropsch synthesis, the catalysts prepared using mechano-synthesis methods showed catalytic performance comparable to the catalysts prepared by impregnation.     

Kinetics of thiophene hydrodesulfurization over a supported Mo–Co–Ni catalyst

In this study, the kinetics of thiophene (TH) hydrodesulfurization (HDS) over the Mo–Co–Ni-supported catalyst was investigated. Trimetallic catalyst was synthesized by pore volume impregnation and the metal loadings were 11.5 wt % Mo, 2 wt % Co, and 2 wt % Ni. A large surface area of 243 m²/g and a relatively large pore volume of 0.34 cm³/g for the fresh Mo–Co–Ni-supported catalyst indicate a good accessibility to the catalytic centers for the HDS reaction. The acid strength distribution of the fresh and spent catalysts, as well as for the support, was determined by thermal desorption of diethylamine (DEA) with increase in temperature from 20 to 600 °C. The weak acid centers are obtained within a temperature range between 160 and 300 °C, followed by medium acid sites up to 440 °C. The strong acid centers are revealed above 440 °C. We found a higher content of weak acid centers for fresh and spent catalysts as well as alumina as compared to medium and strong acid sites. The catalyst stability in terms of conversion as a function of time on stream in a fixed bed flow reactor was examined and almost no loss in the catalyst activity was observed. Consequently, this fact demonstrated superior activity of the Mo–Co–Ni-based catalyst for TH HDS. The activity tests by varying the temperature from 200 to 275 °C and pressure from 30 to 60 bar with various space velocities of 1–4 h^?1 were investigated. A Langmuir–Hinshelwood model was used to analyze the kinetic data and to derive activation energy and adsorption parameters for TH HDS. The effect of temperature, pressure, and liquid hourly space velocity on the TH HDS activity was studied.     

Base-free aerobic oxidation of glycerol on TiO_2-supported bimetallic Au–Pt catalysts

The aerobic oxidation of glycerol provides an economically viable route to glyceraldehyde, dihydroxyacetone and glyceric acid with versatile applications, for which monometallic Pt, Au and Pd and bimetallic Au–Pt, Au–Pd and Pt–Pd catalysts on Ti O2 were examined under base-free conditions. Pt exhibited a superior activity relative to Pd, and Au–Pd and Pt–Pd while Au was essentially inactive. The presence of Au on the Au–Pt/Ti O2 catalysts led to their higher activities(normalized per Pt atom) in a wide range of Au/Pt atomic ratios(i.e.1/3–7/1), and the one with the Au/Pt ratio of 3/1 exhibited the highest activity. Such promoting effect is ascribed to the increased electron density on Pt via the electron transfer from Au to Pt, as characterized by the temperature-programmed desorption of CO and infra-red spectroscopy for CO adsorption. Meanwhile,the presence of Au on Au–Pt/Ti O2, most like due to the observed electron transfer, changed the product selectivity, and facilitated the oxidation of the secondary hydroxyl groups in glycerol, leading to the favorable formation of dihydroxyacetone over glyceraldehyde and glyceric acid that were derived from the oxidation of the primary hydroxyl groups. The synergetic effect between Au and Pt demonstrates the feasibility in the efficient oxidation of glycerol to the targeted products, for example, by rational tuning of the electronic properties of metal catalysts.     

Crystal structure of natural Ag–Cu–Pb–Bi sulfide

The crystal structure of a natural sulfide Cu_3,44Ag_0,56Pb₂Bi₆S₁₃ (Сmcm, Z = 4, a = 3.973(1) Å, b = 13.370(2) Å, c = 42.182(7) Å, R = 0.059) is determined. The structure has seven cation positions: two of them (Cu and Ag) are in a tetrahedral environment of sulfur atoms; one (Pb), in a special position (mm2), has a coordination polyhedron in the form of a bicapped trigonal prism; and the other cation positions are surrounded by sulfur atoms forming distorted octahedra. The mirror symmetry plane perpendicular to the c translation causes microtwinning by cutting a layer of trigonal prisms framed by tetrahedron ribbons. These layers are divided by those composed by edge-linked octahedra with a diagonal ribbon of five octahedra (N = 5). The cation and anion positions are ordered by individual sublattices with pseudohexagonal subcells on the m planes perpendicular to the a translation, which concentrate the positions of all the atoms. Supposedly, this natural sulfide is the previously described (1885) yet unconfirmed alaskaite mineral from the lillianite–heyrovskyite homological series and may be isostructural to the ourayite mineral.     

Molar Volume Calculation of Molten Ag–Au–Cu and Cu–Ag–In Alloy Systems Using General Solution Model

Russian Journal of Physical Chemistry A - However, up to the present, there was few reports on the density of the molten Ag–Au–Cu and Cu–Ag–In alloy systems. In this work,...     

Low-temperature hydrogenation of maleic anhydride to succinic anhydride and γ-butyrolactone over pseudo-boehmite derived alumina supported metal(metal = Cu,Co and Ni) catalysts

The pseudo-boehmite derived alumina supported metal(Cu,Co and Ni) catalysts prepared by the impregnation method were investigated in hydrogenation of maleic anhydride(MA) to succinic anhydride(SA) and γ-butyrolactone.The catalysts were characterized by ICP-AES,N_2 adsorptiondesorption,XRD,H_2-TPR,CO-TPD,dissociative N_2O adsorption and TEM and the results showed that the alumina possessed mesoporous feature and the metal species were well dispersed on the support.Compared to Cu/Al_2O_3 and Co/Al_2O_3,Ni/Al_2O_3 exhibited higher catalytic activity in the MA hydrogenation with 92%selectivity to SA and nearly 100%conversion of MA at 140 °C under 0.5 MPa of H_2 with a weighted hourly space velocity of 2 h ~1(MA).The stability of Ni/Al_2O_3 catalyst was also investigated.     

Co–Cu–La catalysts for selective CO2 hydrogenation to higher hydrocarbons

Copper and lanthanum promoted cobalt catalysts for CO₂ hydrogenation to higher hydrocarbons are described. The catalysts were prepared by the self-propagating high-temperature synthesis followed by alkaline leaching. They are active in CO₂ hydrogenation at 200 °C under 10 bar pressure (CO₂ : H₂ = 1 : 3) with selectivity to C₂₊ alkanes up to 39%; no alkenes and alcohols are formed under these experimental conditions.     

Oxidation of L-sorbose and 2,3;4,6-di-O-isopropylidene-α-L-sorbose over supported platinum and palladium catalysts

Oxidation of L-sorbose and 2,3;4,6-di-O-isopropylidene--L-sorbose by oxygen (air) has been studied over supported Pt and Pd catalysts. The results indicate that the activity and stability of these catalysts are greatly dependent on their composition and preparation conditions.

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L- 2,3;4,6--O---L- () . , .

     

New approaches to prepare supported Sn?Pt bimetallic catalysts

General principles of modification of supported Pt catalysts with tin tetraalkyls are summarized and a new approach to prepare supported Sn−Pt catalysts is described. The new approach leads to the formation of Multilayered Organometallic Complexes (MLOC) anchored onto supported platinum. The formed MLOC can be decomposed either in reductive or oxidative atmosphere with the formation of new type of supported Sn−Pt catalysts with high Sn/Pt_s ratios. The decomposition in a reductive atmosphere leads to the formation of alloy-type bimetallic phases, while the decomposition in the presence of oxygen provides Lewis-acid type surface species anchored to supported platinum. Dedicated to Professor Pál Tétényi on the occasion of his 70th birthday     

Ammoxidation of ethylene to acetonitrile over chromium or cobalt alumina catalysts prepared by sol–gel method

A series of Cr/Al₂O₃ and Co/Al₂O₃ catalysts were tested in the selective ammoxidation of ethylene to acetonitrile. Catalysts were prepared either by sol–gel method or by impregnation with chromium or cobalt acetylacetonate salts. Physicochemical properties of catalysts were accomplished by several techniques such as chemical analysis, physisorption of N₂, X-ray diffraction (XRD), ²⁷Al MAS NMR, UV–Visible diffuse reflectance (DRS) and Raman spectroscopy and temperature programmed reduction of H₂ (H₂–TPR). Textural analysis reveals that mesoporous materials with pronounced surface areas were obtained using sol–gel procedure while impregnation of the support produces a moderate decrease of its surface area and pore volume. XRD analysis confirms the presence of highly dispersed metal species which reside essentially on the surface and measure less than 4 nm. Furthermore, ²⁷Al MAS NMR shows that for xerogels, part of metal species occupies sites on/in A1₂O₃ in close vicinity of octahedral ²⁷Al. This, apparently, is not the case for aerogels. For Cr/Al₂O₃ catalysts, isolated Cr⁶⁺, mono and polychromate species were identified using DRS, Raman Spectroscopy and H₂–TPR which seem to play a key role in the ammoxidation of ethylene. Furthermore, for cobalt doped catalysts, CoAl₂O₄ was identified as active phase on the basis of DRS and H₂–TPR results. From the supercritical drying, it results generally better catalysts than catalysts calcined by ordinary procedure which leads to inactive agglomerated Co₃O₄ and CoO–Al₂O₃ phase.     

Catalytic oxidation of NO over Mn–Co–Ce–Ox catalysts: effect of reaction conditions

Manganese–cobalt–cerium oxide (Mn–Co–Ce–Ox) catalysts were synthesized by the co-precipitation method and tested for activity in low-temperature catalytic oxidation of NO in the presence of excess O₂. With the best Mn–Co–Ce mixed-oxide catalyst, approximately 80 % NO conversion was achieved at 150 °C and a space velocity of 35,000 h^?1. The effect of reaction conditions (reaction temperature, volume fractions of NO and O₂, gas hourly space velocity (GHSV), and catalyst stability) was investigated. The optimum reaction temperature was 150 °C. Increasing the O₂ content above 3 % results in almost no improvement of NO oxidation. This catalyst enables highly effective removal of NO within a wide range of GHSV. Furthermore, the stability of the Me–Co–Ce–Ox catalyst was excellent; no noticeable decrease of NO conversion was observed in 40 h.     

Effects of cobalt carbide on Fischer–Tropsch synthesis with MnO supported Co-based catalysts

Cobalt carbide(Co_2C)was considered as potential catalysts available for large-scale industrialization of transforming syngas(H_2 and CO)to clean fuels.Herein,we successfully synthesized Co-based catalysts with MnO supported,to comprehend the effects of Co_2C for Fischer–Tropsch synthesis(FTS)under ambient conditions.The huge variety of product selectivity which was contained by different active sites(Co and Co_2C)has been found.Furthermore,density functional theory(DFT)shows that Co_2C is efficacious of CO adsorption,whereas is weaker for H adsorption than Co.Combining the advantages of Co and Co_2C,the catalyst herein can not only obtain more C_(5+)products but also suppress methane selectivity.It can be a commendable guide for the design of industrial application products in FTS.     

Preparation and characterization of Ru?Pb supported catalysts

Decomposition of Mn₃Mo₂TeO₁₂ during oxidation of toluene to benzaldehyde was observed. Depending on the surface composition of the initial catalyst, the decomposition leads to less active but highly selective MnMoTeO₆ or to MnMoO₄ which is not selective in toluene oxidation.

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Mn₃Mo₂TeO₁₂ . , MnMoTeO₆, MnMoO₆.