Precursor Of Active Component Research Articles

Hydrogenation of Acetylene over Pd–Ag/Sibunit Catalysts: Effect of the Deposition Sequence of Active Component Precursors

The study investigates interactions between palladium and silver in Pd–Ag bimetallic catalysts supported on a mesoporous carbon material Sibunit and, in particular, the dependence of these interactions on the deposition sequence of the metal precursors. Using XRD and TEM results, it was shown that impregnating the support with an aqueous solution that contained nitrate salts of both metals, followed by hydrogen treatment at 500°C, generates uniformly sized Pd0.6Ag0.4 particles (dav = 5.6 nm). These particles exhibit high selectivity (79%) in the reaction of acetylene hydrogenation to ethylene. The catalysts synthesized by sequential impregnation of the support with solutions of Pd and Ag nitrates interleaved with heat treatment in H2 exhibited a lower selectivity (68–73%) due to the formation of particles non-uniform both in composition and size (about 4 to 60 nm). The IR spectroscopy data suggest this effect is presumably associated with the removal of O-containing functional groups from the carbon surface during the reduction of the supported precursor. Given that O-groups act as anchoring sites for the precursors of active components and suppress the ability of Sibunit to reduce metals from their salt solutions, the subsequent deposition of the second metal salt causes a non-uniform distribution of this metal on the surface and the generation of larger particles.

Hydrogenation of Acetylene over Pd–Ag/Sibunit Catalysts: Effect of the Deposition Sequence of Active Component Precursors

The study investigates interactions between palladium and silver in Pd–Ag bimetallic catalysts supported on a mesoporous carbon material Sibunit and, in particular, the dependence of these interactions on the deposition sequence of the metal precursors. Using XRD and TEM results, it was shown that impregnating the support with an aqueous solution that contained nitrate salts of both metals, followed by hydrogen treatment at 500°C, generates uniformly sized Pd0.6Ag0.4 particles (dav = 5.6 nm). These particles exhibit high selectivity (79%) in the reaction of acetylene hydrogenation to ethylene. The catalysts synthesized by sequential impregnation of the support with solutions of Pd and Ag nitrates interleaved with heat treatment in H2 exhibited a lower selectivity (68–73%) due to the formation of particles non-uniform both in composition and size (about 4 to 60 nm). The IR spectroscopy data suggest this effect is presumably associated with the removal of O-containing functional groups from the carbon surface during the reduction of the supported precursor. Given that O-groups act as anchoring sites for the precursors of active components and suppress the ability of Sibunit to reduce metals from their salt solutions, the subsequent deposition of the second metal salt causes a non-uniform distribution of this metal on the surface and the generation of larger particles.

Nickel Catalysts on Carbon-Mineral Sapropel-Based Supports for Liquid-Phase Hydrogenation of Nitrobenzene

Nickel catalysts with carbon-mineral supports derived from sapropel were synthesized; the effect exerted by the nature of the support (type of the initial sapropel) and active component precursor on the activity of the catalysts in the model reaction of liquid-phase nitrobenzene hydrogenation was studied. The catalysts, synthesized using the support with a smaller fraction of carbon, were more active irrespective of the precursor nature. The highest activity was observed for the catalysts synthesized from nickel nitrate and formate; nitrobenzene conversion was 65% and 51%, respectively, after 1 h of reaction. The catalysts retained high activity after six reaction cycles at 100% aniline selectivity. The presence of sulfur in the nickel precursor deteriorated the catalytic activity (convection less than 3%) due to formation of the sulfide phase.

Stability of novel eco-friendly sulfated metal oxide solid acid catalyst for esterification and condensation reaction

<h2>Abstract</h2> In this paper, the metal oxide supports and active component precursors of SO₄²⁻/M_xO_y solid acid were screened, and S₂O₈²‐⁻/Cr₂O₃-Fe₂O₃ (S₂-CrFe) was prepared. The NH₃-TPD results showed that the solid acids loaded with S₂O₈²⁻ had stronger acidity than those loaded with SO₄²⁻, and the mixture of the two metal oxides could adjust the acidity of the solid acids. The optimum conditions for the preparation of S₂-CrFe were as follows: the mass ratio of Cr₂O₃ to Fe₂O₃ was 1:1, the concentration of ammonium persulfate solution was 1 mol/L, and the calcination temperature was 550 °C. The yield of esterification catalyzed by the solid acid obtained under these conditions was 91.2%. The stability of the new solid acid was investigated, and it was found that S₂-CrFe was easy to be deactivated, so it was considered to be modified by organosilane and lanthanum oxide. The experimental results showed that after the modified solid acid was recycled for four times, the yield of ethyl acetate was more than 60%.

Influence of a synthesis method and a support nature on physicochemical and catalytic properties of supported rhodium catalysts for the partial oxidation of hydrocarbons. I. Chloride series

Abstract Rhodium catalysts supported on bayerite and pseudoboehmite alumina, calcined at 800 °С, were synthesized and tested in the partial oxidation of methane. Rhodium (III) chloride was used as an active component precursor. The supports and catalysts were investigated by a wide range of physicochemical methods: XRD, SEM and HR TEM, XPS and UV–vis DRS. In both cases, large rhodium particles with a coherent scattering region size of 15–19 nm are formed, and small ones with dimensions less than 1 nm. On the whole, smaller rhodium particles are formed on the bayerite oxide. The catalyst with pseudoboehmite-type support shows better results in the reaction.

Development of Approaches to the Formation of Platinum Sites with Desired Properties Using Layer-Structured Supports

Specific properties of layered double hydroxides (LDHs), directions of their use as supports and support precursors for synthesis of catalysts, and advantages of using such catalysts for various reactions were considered. The possibility to vary the chemical composition of LDHs (cationic layers, interlayer space) without destroying the structure of the material allows tuning their adsorption and acid-base properties and selectively realizing various mechanisms of anchoring the active component precursor toward preparing highly dispersed and stable supported catalysts. Approaches to the formation of supported platinum particles with desired properties through changing the anionic and cationic compositions of LDHs were proposed for the Pt/MgAl(M)-LDH system taken as an example.

Porous nickel-based catalysts for tri-reforming of methane to synthesis gas: Preparation and characterization

The effect of synthesis conditions on the phase composition and texture of porous nickel ribbon with a MgO underlayer and of nickel catalysts supported on it was studied. The MgO underlayer was prepared by impregnation of a nickel ribbon with a Mg(NO3)2 or Mg(CH3COO)2 water solutions and subsequent calcination at 750 °C in H2. The formation of more dispersed MgO was observed with the use of Mg(NO3)2 as precursor. Catalysts were prepared by supporting of nickel onto nickel ribbon with MgO underlayer by its impregnation with a mixture of solutions of Ni(NO3)2 and Mg(NO3)2 followed by thermal pre-treatment in N2 or in He. Under reduction the formation of highly dispersed nickel crystallites (3–5 nm) epitaxially bound to MgO was observed in the catalysts with MgO underlayer prepared from Mg(NO3)2 with thermal pre-treatment of the precursor of active component in N2 or He. The supported nickel catalysts showed stable activity in tri-reforming of methane throughout the test period (9 h).

Structured catalytic cartridges for SO2 oxidation in flue gases of coal-fired powerplants

Structured glass-fiber catalysts (GFC) are considered for application in the process of oxidation of endogenous SO2 directly in the media of flue gases from coal-fired powerplants. Such oxidation may be used for conditioning of flue gases to improve the efficiency of ash particulates in electrostatic precipitators. Comparison of Pt-based and vanadia-based GFC showed the much better performance by Pt/GFCs, having much higher activity and significantly lower ignition temperature (~300 °C). The best performance is demonstrated by Pt/GFC synthesized by high-temperature synthesis method in combination with spraying of active component precursor solution on the glass-fiber support surface instead of conventional impregnation. Application of structured GFC cartridges makes possible to apply them directly inside the flue gas duct with appropriate pressure drop. High permeability of such cartridges makes possible to apply them in the gas fluid contaminated with ash particulates with minimized risk of clogging. Beyond the mentioned advantages, application of GFC may be useful for resolution of related environmental problems: incineration of polyaromatic compounds and mercury-containing organic substances in flue gases.

Pyrolytic Carbon-coated Cu-Fe Alloy Nanoparticles with High Catalytic Performance for Oxygen Electroreduction.

Well-dispersed carbon-coated or nitrogen-doped carbon-coated copper-iron alloy nanoparticles (FeCu@C or FeCu@C-N) in carbon-based supports are obtained using a bimetallic metal-organic framework (Cu/Fe-MOF-74) or a mixture of Cu/Fe-MOF-74 and melamine as sacrificial templates and an active-component precursor by using a pyrolysis method. The investigation results attest formation of Cu-Fe alloy nanoparticles. The obtained FeCu@C catalyst exhibits a catalytic activity with a half-wave potential of 0.83 V for oxygen reduction reaction (ORR) in alkaline medium, comparable to that on commercial Pt/C catalyst (0.84 V). The catalytic activity of FeCu@C-N for ORR (Ehalf-wave =0.87 V) outshines all reported analogues. The excellent performance of FeCu@C-N should be attributed to a change in the energy of the d-band center of Cu resulting from the formation of the copper-iron alloy, the interaction between alloy nanoparticles and supports and N-doping in the carbon matrix. Moreover, FeCu@C and FeCu@C-N show better electrochemical stability and methanol tolerance than commercial Pt/C and are expected to be widely used in practical applications.

Catalytic device on the base of glass-fiber catalyst for environmentally safe combustion of fuels and utilization of toxic wastes

The work is dedicated to development of the optimal glass-fiber catalyst (GFC) for the process of environmentally efficient combustion of hydrocarbon fuels and utilization of organic wastes. The primary selection of catalysts using the test reaction of toluene oxidation in air showed that the best activity and minimum formation of by-products is observed at Pt-containing GFCs. Among them the best efficiency is observed for the GFCs prepared by spraying of active component precursor instead of conventional impregnation method; they are characterized with higher uniformity of active component deposition across the fiber surface and higher dispersion of Pt particles leading to their higher activity, despite lower Pt content. The prototype of the device for combustion of hydrocarbon fuels was made on the base of structured Pt/GFC cartridge. The tests performed with LPG fuel showed the achievement of planned heat power of 15 kW, practical absence of NOx and minimum CO and hydrocarbon content in the combustion products. The developed combustor may be used for direct air heating in various rooms and buildings, as well as for utilization of toxic organic wastes.

Развитие подходов к формированию платиновых центров с заданными свойствами с использованием носителей со слоистой структурой

Рассмотрены особенности слоистых двойных гидроксидов (СДГ) с точки зрения перспективы их использования в качестве носителей и предшественников носителей для получения нанесенных металлических катализаторов и преимущества таких катализаторов в реакциях различного типа. Возможность варьирования химического состава СДГ (состава катионных слоев, межслоевого пространства) без разрушения структуры материала позволяет регулировать его адсорбционные и кислотно-основные свойства, селективно реализовать различные механизмы закрепления предшественника активного компонента для получения высокодисперсных и стабильных нанесенных катализаторов. На примере системы Pt/MgAl(M)-СДГ предложены подходы к формированию частиц нанесенной платины с заданными свойствами посредством изменений в анионном и катионном составе СДГ.

Influence of the phosphorus addition ways on properties of CoMo-catalysts of hydrotreating

CoMo-hydrotreating catalysts differed in the way of P addition were studied. The phosphorus was added in catalysts as follows: into the kneading paste of an alumina support, by impregnation of an alumina support before impregnation by active metals and into impregnation solution jointly with active metals. Impregnating solutions, supports and catalysts were studied by the nitrogen adsorption-desorption, UV–vis spectroscopy, RAMAN and ATR-FTIR spectroscopies, HRTEM, EDX, XPS. Catalysts were tested in hydrotreating of model feed. It was established that adding of P into the kneading paste or by impregnating of a support influenced negatively catalytic activity. Negative effect was caused by the formation of CoAl2O4 compounds and reduced portion of cobalt in the content of active phase. The addition of phosphorus into impregnation solution results in a significant increase in catalytic activity in the hydrodesulfurization of dibenzothiophene. In this case, phosphorous results in the change in the structure of active component precursors, the increase in the stacking number of the active component particles, the decrease in the interaction between active metals and a support. It was shown that the most efficient way to improve catalysts by P is to add its precursor into impregnating solution.

Developing Effective Cobalt Catalysts for Hydrogen-Generating Solid-State NaBH4 Composite

Hydrogen-generating solid-state NaBH4 composite are promising systems for storing and transporting hydrogen intended for use in low-temperature proton-exchange membrane fuel cells. Catalysts are introduced into the composites to ensure the generation of hydrogen at ambient temperatures. In this work, the effect of the synthesis conditions for cobalt catalyst on the gas generation rate is analyzed. It is found that the efficiency of hydrogen generation depends on the nature of the cobalt salt and pH of the aqueous solution of the salt in which the active component precursor is reduced under the action of sodium borohydride because these factors determine the composition, degree of dispersion, and magnetic behavior of the cobalt systems. It is found that the highest rate of gas generation—505 cm3/min per gram of the composite with a hydrogen content of 8.4 wt %—is observed for a sample reduced with sodium borohydride in a hydrochloric acid solution of cobalt chloride with a pH of 1.3. The results can be used to develop effective inexpensive cobalt catalysts for the production of hydrogen from pelletized solid-state NaBH4 composite.

Effect of the nature of the active-component precursor on the properties of Pt/MgAlO x catalysts in propane and n-decane dehydrogenation

The Pt/MgAlO x catalysts, in which a mixed aluminum–magnesium oxide obtained by the heat treatment of corresponding layered double hydroxides was used as a support, were studied. The effects of the nature of active-component precursors ([PtCl6]2–, [PtCl4]2–, and [Pt3(CO)6] 6 2- ), and the Mg/Al ratio in the support on the anchoring of complexes, the disperse state of platinum, and the properties of the obtained catalysts in the reactions of propane and n-decane dehydrogenation were found.

The effect of preparation conditions of Pd/C catalyst on its activity and selectivity in the aqueous-phase hydrogenation of 2,4,6-trinitrobenzoic acid

The effect of the nature of alkaline agent and pH value of hydrolysis of Pd(II) chloride complex into palladium polynuclear hydroxo complexes, as precursor of active component in Pd/C catalyst, on the dispersion of palladium particles supported on carbon material Sibunit was revealed. It was shown that an increase in the particle size of supported palladium enhances the specific catalytic activity in hydrogenation of 2,4,6-trinitrobenzoic acid and changes the direction of the transformation (increases the fraction of non-aromatic intermediate, cyclohexane-1,3,5-trione trioxime, in the products). The results obtained are essential for optimizing the particle size of supported palladium in selective hydrogenation of polyfunctional organic compounds.

Development of Effective Cobalt Catalysts for Hydrogen-Generating Solid Phase Compositions Based on Sodium Borane

Hydrogen-generating solid phase compositions based on sodium boran are promising systems for storage and transportation of hydrogen to be used for low-temperature fuel cells with proton-exchange membranes. Catalysts are added to the compositions in order to generate hydrogen at ambient temperature. The studies were focused on the influence of conditions of the cobalt catalysts preparation on the rate of gasgeneration. The efficiency of hydrogen evolution depended on the nature of the cobalt salt and pH of its aqueous solution where the active component precursor was reduced under the action of the hydride; these factors determined the composition, dispersion and magnetic behavior of the cobalt systems. The maximal rate of gas generation (505 cm 3 /min per 1 g of the composition containing 8.4 wt % of hydrogen) was observed in the presence of the sample reduced by sodium borane in a cobalt chloride solution with pH 1.3. The results obtained can be used to develop effective and inexpensive cobalt catalysts for generation of hydrogen from solid compositions based on sodium borane.

Targeted synthesis of a copper catalyst with a nanostructured active component

The effect of the hydrodynamic regime in the stirring of a copper carbonate–ammonia suspension containing an alumina–silica support on the chemical and phase composition of an active component (AC) precursor for a catalyst of cyclohexanol dehydrogenation to cyclohexanone is studied. By means of X-ray diffraction, differential thermal analysis, and adsorption, the precursor is found to precipitate in a developed turbulent regime, predominantly in the form of nanostructured hydroxocarbonate structures strongly bonded to the support. Some catalytic and textural properties of CAS-C (copper–alumina–silica for caprolactam) samples are studied with AC contents of 20 to 30 wt % (on a copper oxide basis). The laboratory technology is scaled up to industrial conditions. CAS-C samples and commercial H3-11 catalyst (BASF) are subjected to catalytic tests (in a flow-type reactor with a fixed catalyst bed 40 cm3 in volume at a temperature of 250°C and atmospheric pressure). The CAS-C catalyst is shown to be similar to the H3-11 catalyst in terms of selectivity, and to considerably surpass it in activity and thermal stability.

Deliberate Synthesis of a Copper Catalyst with a Nanostructured Active Component

The influence of hydrodynamic mode of mixing a copper-ammonium-carbonate slurry containing aluminosilica support on the chemical and phase composition of the active component (AC) precursor of the catalyst for dehydrogenation of cyclohexanol in the production of caprolactam was studied. XPS, DTA and adsorption techniques were used to establish that, under conditions of the advanced turbulent mode, the precursor is mainly deposited in the form of nanostructured hydroxocarbonates anchored tightly to the support. The lab-scale technology was scaled-up to industrial level. Properties of the new copper catalyst were studied to reveal that it is not inferior in the selectivity to the best known industrial (commercial) catalysts, but superior to them in the activity and thermostability.

Effect of temperature-programmed pyrolysis pre-treatment on desulfurization performance of Zn-based sorbent prepared by lignite as support

A series of Zn-based sorbents were prepared by high-pressure impregnation with lignite as precursor of support and zinc nitrate as the precursor of active component, followed by temperature-programmed pyrolysis of the impregnated lignite sample in a fixed-bed quartz reactor. The H2S removal performances of sorbents prepared under different pyrolysis conditions such as temperatures, holding time as well as heating rates were evaluated. The physical and chemical properties of sorbents were characterized by atomic absorption spectroscopy (AAS), X-ray diffraction (XRD), transmission electron microscope (TEM) and nitrogen adsorption techniques. The results show that the process of pyrolysis can improve the pore structure dramatically, which lead to the high specific surface area and large pore volume. The good desulfurization performance of sorbent was attributed to both of the proper porous structure of sorbents, the content and distribution of active component. The optimal operating conditions of temperature-programmed pyrolysis for the impregnated lignite sample were the heating rate of 10°C/min, holding time of 180min in N2 atmosphere and pyrolysis temperature of 550°C. The sulfidation time could hold for over 720min before reaching 1ppm H2S in outlet gases and the sulfur capacity was up to 25.91g S/100g ZnO for sorbent prepared under this optimized condition.

The features of the CO disproportionation reaction over iron-containing catalysts prepared by different methods

The peculiarities of the CO disproportionation reaction over iron-containing catalysts have been studied. The reaction is known to be reversible and resulting in a direct path to the formation of carbon deposits and CO2. The iron-containing catalysts (1–5 wt% of Fe) were prepared by three different methods: co-precipitation of Fe- and Al-containing precursors, impregnation of γ-Al2O3 support with iron nitrate, and solution combustion synthesis (SCS). The latter technique is based on self-propagating combustion of active component precursor with fuel additive deposited on surface of fiberglass. The synthesized samples were characterized with physicochemical methods and tested in CO disproportionation reaction within the temperature range of 120–600 °C. The co-precipitated catalyst 5 wt% Fe–Al2O3 showed the highest activity (45 % conversion of CO) which is much superior to that observed for other catalysts in this reaction. According to SEM, CO disproportionation reaction has resulted in carbon deposition in both amorphous and nanostructured forms. It was shown that preparative technique has significant effect on catalytic performance of iron-containing catalysts.