Catalysts Of Various Compositions Research Articles

Patterns of Formation of Binary Cobalt–Magnesium Oxide Combustion Catalysts of Various Composition

In order to establish the formation patterns of the Co–Mg oxide system, samples with different Co:Mg ratios and heat treatment temperatures were synthesized and studied. A study of the samples confirmed the phase transition of MgxCo2–xO4 spinels into the corresponding solid solutions at 800–900 °C. The similarity of the formation patterns for different compositions is shown. The rocksalt oxide in low-temperature samples is an anion-modified paracrystalline phase that forms a “true” solid solution only upon spinel decomposition. The TPR profiles of the decomposed Co3O4 spinel show surface Co3O4 peaks and a wide peak corresponding to the well-crystallized CoO, while partial Co3O4 TPR up to 380 °C results in dispersed and amorphous CoO. The high-temperature non-stoichiometric samples are poorly reduced, indicating their low oxygen reactivity. Spinel reoxidation after heat treatment to 1100 °C by calcination at 750 °C showed complete regeneration for MgCo2O4–Co3O4 samples and its absence in case of an excess of MgO relative to stoichiometry.

THE ROLE OF Zn-Fe CATALYSTS IN THE REACTION OF ETHANOL CONVERSION TO ACETONE

Recently, processes for obtaining various organic compounds from ethanol, which is derived from the processing of plant raw materials, have become highly relevant. Acetone is a valuable monomer that can be obtained from ethanol. It has been previously demonstrated that catalysts based on zinc oxides exhibit high activity in the conversion of ethanol to acetone. A review of the literature has shown that catalysts based on iron oxides also demonstrate high activity in this reaction. Therefore, the aim of this work was to study the vapor-phase conversion of ethanol to acetone on various binary zinc-iron oxide catalysts. This article describes a process for studying the paraphase conversion of ethanol to acetone on zinc-iron oxide catalysts Zinc-iron oxide catalysts of various compositions have been synthesized. The activity of the obtained catalysts was studied in the reaction of ethanol conversion. It was shown that samples rich in zinc oxide exhibit the greatest activity in the studied reaction. It has been established that the yield of acetone on the best catalysts reaches its maximum yield. The zinc-iron oxide catalyst of composition 9:1 showed the highest activity. catalyst, the maximum yield of acetone reaches up to 80%. Keywords: catalyst, ethanol, acetone, zinc, iron, vapor-phase conversion, iron oxides, temperature, reaction rate.

Enhanced alkaline hydrogen oxidation reaction using electrodeposited Ni-Ir alloy catalysts

The development of high-performance non/less-precious metal-based electrocatalysts for the hydrogen oxidation reaction (HOR) in anion exchange membrane fuel cells remains a challenge. Here, we report a bimetallic Ni-Ir catalyst fabricated using electrodeposition and optimized to improve its HOR performance in an alkaline environment. Bimetallic Ni-Ir catalysts of various compositions are electrochemically deposited on a glassy carbon (GC) disk electrode and their HOR activity in 0.1 M KOH is examined. It is found that Ni47Ir53 has the highest HOR activity of 2.09 and 2.28 mA cm−2 at 0.05 and 0.10 VRHE, respectively, outperforming a commercial Pt/C electrode. This improved performance is ascribed to the larger electrochemical surface area and the modification to the electronic structure via alloying. Electrochemical analysis revealed a low Tafel slope and a large exchange current density for Ni47Ir53, suggesting the presence of the Tafel-Volmer mechanism and a rapid Volmer reaction. The balanced H binding and OH binding with Ni47Ir53 is a significant contributor to the higher HOR activity. During accelerated durability testing, the oxidation state and electronic structure of the catalyst become more unfavorable for the HOR due to Ni dissolution, which supports the strategy of employing a dissolution-resistive alloying metal with Ir for alkaline HOR catalysts.

Steam/CO2 Reforming of Methane Over Impregnated Ni/CeO2 Catalysts: Effect of Sample Composition on Their Activity and Stability

Steam/CO2 reforming of methane was studied at 600–900 °C, molar ratio CO2/H2O 0–2 and contact time 0.04–0.15 s over impregnated Ni/CeO2 catalysts of various compositions. It has been established that with an increase in the Ni content from 2 to 10 wt.%, both the conversion of reactants (X) and the yield of products (Y) increase in the range XCH4 25→80%, XCO2 35→72%, YH2 30→80%, YCO 30→75% (at 750 °C). With a further increase in the nickel content to 15%, the process parameters changed slightly, reaching a plateau. Higher nickel content (10 vs. 2 wt.%) ensures stable operation of the catalyst over time. The functional performance of the catalysts was correlated with physicochemical properties of as-synthesized, activated and spent samples using X-ray fluorescence analysis, low-temperature nitrogen adsorption, X-ray diffraction analysis, electron microscopy, and thermal analysis. It was shown that the Ni content affects the thermal stability, the textural, structural and redox characteristics of the samples. The 10% Ni/CeO2 catalyst was chosen as the optimal one due to higher H2 productivity, and sufficient resistance to sintering and coking. This sample provides a stable hydrogen yield of 85% in steam/CO2 reforming of methane at 800 °C, CO2/H2O = 2 and a contact time 0.15 s.

Joint Cracking of Vacuum Gasoil with Vegetable Oils on Zeolite-Containing Catalysts of Various Compositions

Joint Cracking of Vacuum Gasoil with Vegetable Oils on Zeolite-Containing Catalysts of Various Compositions

Oxygen reduction reaction on electrodeposited PtAu alloy catalysts in the presence of phosphoric acid

We have investigated phosphate adsorption on the Au surface by in situ electrochemical surface-enhanced Raman spectroscopy to assess the possible use of Au-based alloys as catalysts for the oxygen reduction reaction (ORR) in high-temperature proton exchange membrane fuel cells. Compared with its strong adsorption in neutral or basic electrolytes, the adsorption of phosphate species on the Au surface were significantly altered in acidic electrolyte. Thus, PtxAu100-x catalysts of various compositions were prepared by electrodeposition and exhibited better ORR activities than pure Pt in phosphoric acid electrolyte, which can be explained in terms of alloying effects and the different phosphate adsorption behavior.

Electrocatalytic activity of atomic layer deposited Pt–Ru catalysts onto N-doped carbon nanotubes

Pt–Ru catalysts of various compositions, between 0 and 100at.% of Ru, were deposited onto N-doped multi-walled carbon nanotubes (N-CNTs) by atomic layer deposition (ALD) at 250°C. The Pt and Ru precursors were trimethyl(methylcyclopentadienyl)platinum (MeCpPtMe3) and bis(ethylcyclopentadienyl)ruthenium (Ru(EtCp)2), respectively. O2 was used as the reactant in both processes. The composition of the catalysts was easily tuned by varying the Pt-to-Ru ALD cycle ratio. The catalysts were tested toward the CO oxidation and methanol oxidation reaction (MOR) in a three-electrode electrochemical set-up. For the compositions investigated, the catalysts with a Ru content of 29at.% exhibited highest catalytic activity.

Effect of oxidative heat-treatment on electrochemical properties and oxygen reduction reaction (ORR) activity of Pd–Co alloy catalysts

Pd–Co catalysts of various compositions are subjected to heat-treatment in an oxygen-containing atmosphere (5% oxygen and 95% argon by volume) and the catalysts are found to form oxides. On exposure to electrochemical conditions, the oxides get reduced in the potential range of 0.05–0.4V of the voltammogram and the voltammetric features of the heat-treated catalyst are comparable to that of the corresponding as-prepared catalyst of same composition. The trends in electrochemical surface area (ESA), current due to formation of adsorbed-oxygenated species and activity towards oxygen reduction reaction (ORR) with catalyst composition are similar and they are in the order of Pd≪Pd1.5Co<PdCo<Pd6.3Co<Pd2Co<Pd3Co. The ORR activity of the catalyst subjected to the oxidative thermal treatment is higher than that of Pd and the corresponding as-prepared catalyst of same composition.

Copper-containing catalysts for the oxidative dehydrogenation of organic compounds

A method of doping magnesium aluminum hydrotalcites, which are precursors for oxidative dehydrogenation oxide catalysts of various compositions, with copper(II) was developed, and copper(II)-containing oxide catalyst samples were synthesized. The catalytic properties of these catalysts were studied in the oxidative dehydrogenation of ethane, propane, and hexane. The conversion of ethane into ethylene on the copper-containing catalysts was established to proceed with high selectivities (90–97%) and at low temperatures (400–450°C).

Oxidative ammonolysis of 3- and 4-methylpyridines on vanadium oxide catalysts modified with titanium and tin oxides

Catalytic properties of vanadium-titanium-tin oxides catalysts of various compositions were studied in oxidative ammonolysis of 3- and 4-methylpyridines.

New generation of supported Ziegler-type catalysts for polyethylene production

On the basis of new methods of synthesis of magnesium-containing carriers with the use of soluble organomagnesium compounds a wide spectrum of supported titanium-magnesium and vanadium-magnesium catalysts of various composition with controllable optimal morphology for obtaining versatile brands of polyethylene by suspension and gas-phase methods was elaborated. The usage of various modifications of these catalysts allows production of high amount (up to 1000 kg/g Ti) of polyethylene of high, medium, and low density with narrow and wide molecular weight distribution (including bimodal) as well as different brands of polyethylene ultrahigh molecular weight.

Tungsten-containing catalysts for oxidative dehydrogenation of hydrocarbons

Methods for introducing tungsten into the precursors of oxide catalysts for oxidative dehydrogenation (OD) were developed. Tungsten-containing samples of oxide catalysts of various compositions were synthesized and their catalytic properties in OD of ethane were studied. The introduction of tungsten into the catalysts increased the yield of ethylene in all cases. In the series of tungsten-containing catalysts, the ethylene yield increased in the following order of the catalysis: Mg-Al-V-Mo-W-O < Mg-Al-Ni-V-Mo-W-O < Mg-Al-Fe-V-Mo-W < Mg-Al-Cr-V-Mo-W-O.

Electrocatalytic performance of Ba-doped TiO 2 hollow spheres in water electrolysis

Barium doped titania hollow sphere catalysts of various compositions were prepared and their electrocatalytic performance was evaluated in acidic media. Titania hollow sphere particles were prepared using poly (styrene–methacrylic acid) latex as template material, and BaCl 2 was used precursor material during barium doping over spheres. The morphology and structure of Ba/TiO 2 hollow spheres were characterized by BET, XRD, TGA and TEM analysis. XRD results had confirmed the presence of rutile TiO 2 and BaTiO 3 phases in the catalysts. The catalysts have shown almost similar surface area values (around 97 m 2/g) irrespective of their compositions. On the other hand, surface area values were diminished remarkably with rise in the calcination temperatures. In TEM images, hollow sphere formation with uniform layer of barium over the spheres could clearly be observed. Diameter of Ba-doped TiO 2 hollow sphere was found 0.4–0.5 μm irrespective of the variation in calcination temperatures. In cyclic voltammograms, both the hydrogen and oxygen evolution peaks were present for all the hollow sphere samples; although the peak positions had changed to some extent for few samples. Anodic polarization curves have shown 60 mA cm −2 current density for 20 wt% Ba/TiO 2 hollow sphere sample. Tafel slope is revealed as 122 mV for the same electrocatalyst. Barium doped titania hollow spheres have also shown long time electrocatalytic stability in acid solution.

Titanium-magnesium catalysts for olefin polymerization - effect of titanium oxidation state on catalyst performance

In this work, we investigated the influence of oxidation state of titanium and the effect of ethoxy groups' introduction into titanium compounds on the catalytic properties of MgCl2 - supported catalysts [with triisobutylaluminum (TIBA) or triethylaluminum (TEA) as cocatalyst] in ethylene polymerization and ethylene 1-hexene copolymerization, and on the polymer characteristics. To prepare supported titanium-magnesium catalysts of various compositions, soluble compounds of titanium in different oxidation states [?6-benzene-Ti2+Al2Cl8, Ti3+Cl3źnDBE, and Ti4+(OEt)2Cl2] were synthesized, analyzed by ESR and 13C NMR methods, and immobilized on the highly dispersed magnesium chloride. The data were obtained on the effects produced by composition and oxidation state of titanium compounds (covering also commonly used TiCl4) on the activity, control of PE molecular weight by hydrogen, copolymerization ability, and molecular weight distribution (MWD) of polyethylene. The results obtained demonstrate that different titanium precursors comprising Ti(II), Ti(III) and Ti(IV) compounds supported on MgCl2 allow preparing the highly active catalysts for ethylene polymerization or ethylene/1-hexene copolymerization. It was found that titanium oxidation state in the initial titanium compounds had a weak effect on the molecular weight and MWD of PE, whereas the ligand environment of titanium affected this parameter more strongly.

The Kinetics of the Catalyzed CVD of Monocrystalline α‐Silicon Nitride Filaments

AbstractCatalyzed chemical vapor deposition of α‐silicon nitride filaments from silicon subhydrides and ammonia was studied using calculation of nitrogen solubility in selected catalysts (silicon‐containing iron alloys), both in the solid and liquid‐state, by filament deposition experiments with catalysts of various composition and size, and by variation of the flow rates and partial pressures of precursor gases, the silicon subhydrides and ammonia. The results show that neither nitrogen solubility in, nor nitrogen diffusion through the catalyst plays a determining role in the deposition kinetics, as has been previously suggested. Instead, the deposition rate is determined by the partial dissociation of ammonia, which can be accelerated by adding diluent gases with a sufficiently high collision cross section. The catalyst material has an additional, strongly accelerating effect. The present state of research suggests that nitrogen is the preferred diluent gas and chromium an optimum alloying element.

Investigation of the kinetics of ethylene polymerization with supported titanium‐magnesium catalysts of various composition

AbstractA mathematical model of the polymerization process is suggested on the basis of kinetic data, obtained for the polymerization of ethylene with supported titanium‐magnesium catalysts of various compositions differing in particle size, content of electron donor modifier, oxidation state of titanium in the initial catalyst and combination with different cocatalysts. The model includes stages of the formation and deactivation of active sites and takes into account monomer diffusion into the polymer particle. The analysis of experimental data by means of the mathematical model allowed to obtain the rate constants for single stages of the polymerization process. The suggested model and the obtained set of parameters allow to make a satisfactory description of a wide spectrum of experimental data, corresponding to different shapes of kinetic curves. The kinetic parameters were found to depend on the oxidation state of titanium in the catalyst and on the nature of the cocatalyst.

Activity of catalysts in 1-butanol reaction with H2S

Reaction of 1-butanol with H2S has been studied at 300 °C and 0.1 MPa on catalysts of various composition. The catalysts that contain mainly strong proton sites on their surface accelerate dehydration of alcohol alone. In the presence of catalysts possessing acidic and basic Lewis sites 1-butanethiol is formed. Reaction rate increases as the concentration and strength of Lewis acid sites increase.

Catalytic synthesis of thiolane from tetrahydrofuran and H 2S

Tetrahydrofuran recyclization to thiolane (the Yuriev reaction) was studied in the presence of alumina. Thiolane formation at 200–500°C was found to be accompanied by cracking of both the initial matter and the product, yielding hydrocarbons and coke deposition on the catalyst surface. Catalysts of various composition were investigated. Lewis acid sites appeared to play a prominent role in their activity in the generation of thiolane, i.e., the rate per site increased with the strength of the site. Taking into account kinetic, IR and NMR data, we postulated the reaction mechanism: the interaction between tetrahydrofuran and the catalyst yielded an oxo compound, subsequently dissociating on Al 3+-O − paired sites. Thiolane formed upon interaction of the intermediate alkoxy complexes and H 2S activated on the surface.

Thermocatalytic sensors with Pd-Pt-Al 2O 3 catalyst

The pecularities of the temperature dependence of the output signals of thermocatalytic sensors (TCS), having metal-oxide catalysts of various composition (Pd-Al 2O 3, Pt-Al 2O 3, Pd-Pt-Al 2O 3), annealed in air and in methane-air mixture, in the process of methane detection are investigated. The obtained results were analysed with regard to the data of catalyst phase composition change in situ and of the Pd and Pt valency state. The conclusion was made that one of the possible reasons for the higher output signal stability in thermocatalytic sensors with the Pd-Pt-Al 2O 3 catalyst is the stability increase of Pt in the presence of Pd + and Pd 2+ palladium ion forms, which are most active in the reaction of deep methane oxidation.

Decomposition of alkanethiols to dialkyl sulfides and hydrogen sulfide

Disproportionation of thiol to sulfide and H2S takes place on catalysts of various composition, the most active being those with paired acid-base centers. On these catalysts at 200–400°C methanethiol is quantitatively converted to dimethyl sulfide. Disproportionation of ethanethiol and particularly of 2-propanethiol is accompanied by the decomposition of sulfides formed and initial thiols to produce olefins and H2S.