The modifying effect of cobalt on palladium in novel bimetallic Pd-Co catalysts supported on alpha-alumina was studied, and the catalytic properties of Pd-Co/alpha-Al2O3 samples in the direct selective hydrogenation of acetylene to ethylene were carefully investigated. It was shown that the temperature of catalyst treatment in hydrogen and the Pd/Co ratio are effective tools for varying nanoparticles composition of the Pd(1-x)Cox solid solution formed in the catalysts. Increasing the reduction temperature and decreasing the Pd/Co molar ratio leads to a gradual increase in the Co content in the Pd(1-x)Cox particles, which provides a slight decrease in activity, but an improvement in ethylene selectivity and the yield of the target product. Using XRD, XPS, HR TEM, TPD-C2H4 and TPR-H-2 it was found that an increase in the cobalt concentration in Pd(1-x)Cox nanoparticles suppresses the ability of the active component to activate hydrogen, enhances the electron interaction between Pd and Co and ensures rapid desorption of ethylene from the catalyst surface. The highest selectivity was demonstrated on supported Pd(1-x)Cox nanoparticles with the value of x > 0.4. It was also established that Pd-Co/alpha-Al2O3 samples with Pd:Co = 1:3 and 1:4 reduced in H-2 at 700 degrees C provide a high and stable ethylene yield at a level of 68 % due to the enhanced influence of cobalt on the electronic and geometric properties of palladium in Co-rich PdCo nanoparticles.

The La0.9Sr0.1Sc0.9Co0.1O3-delta (LS) and La0.9Sr0.1CoO3-delta (LC) phases and composite materials based on them were synthesized. There are data in the literature on the activity of pure or modified forms of LC in ammonia decomposition, but there are no data on the activity of the LS phase and LS-LC composites. Therefore, the stability and activity of LS-LC composites and initial LS and LC in ammonia decomposition were investigated. The best result in the decomposition of ammonia at 700 degrees C and WHSV of 60000 ml NH3.g(cat)(-1).h(-1) shows LC - 99%, the worst LS - 80%. Under the same conditions, the activity of samples LC, 40LS-60LC and 50LS-50LC remains unchanged for 40 hours. It was found that during ammonia decomposition, the LC phase decomposes to form cobalt and La(OH)(3) nanoparticles, but the LS phase does not undergo significant changes, which is confirmed by X-ray diffraction, IR spectroscopy, Raman spectroscopy and TEM.

The features of the catalytic action of bimetals such as Pd-Ag, Pd-Cu, Pd-Au, Pd-Ga, Pd-Zn on the conversion of acetylene to ethylene are considered. Two factors that determine the influence of the second metal on palladium – the ensemble effect (geometric effect) and the ligand effect (electronic effect) were taken into account. The relationship between the parameters obtained using calculation methods and experimentally established characteristics are shown. The calculated parameters are thermodynamic and kinetic parameters of the adsorption interaction of the main components of the reaction medium and intermediates with the catalyst surface, the structure of active ensembles and the experimental ones are the structural parameters of bimetallic phases, the electronic state of their components, and catalytic properties of bimetals. The examples illustrating the possibility of the modifier atoms entering into active ensembles and the participation of the sites formed from modifier atoms in the catalysis of individual elementary stages are presented.

Based on analysis of the catalytic properties of 4 ⇌ 2NH3 has been derived to correctly describe the dependence of the chemical reaction rate on the partial pressures of the reaction mixture components for both the forward and reverse reactions. The approach used to derive the kinetic equation is based on the assumption that the adsorption sites of the ruthenium surface are filled with hydrogen, which is subsequently displaced by nitrogen during competitive interaction. Using the proposed kinetic equation, the equilibrium constants and apparent activation energies for ammonia synthesis and decomposition in the presence of 4

The study of ruthenium catalysts for ammonia decomposition on carbonized and non -carbonized Al2O3 nanofibers (ANF) showed that the activity of catalysts with carbonized supports (ANFC) was 2-3 times higher compared to non-carbonized ones. Thus, on Ru/ ANFC and Ru/ANF the release of hydrogen reached 133.5 and 34.7 mmol H2/(min & BULL;gcat), respectively, whereas on Ru-BaAc/ANFC and Ru-BaAc/ANF, only 118.8 and 58.6 mmol H2/ (min & BULL;gcat), respectively. On the average, the activation energy of ammonia decomposition on ANFC-supported catalysts is 15 kJ/mol lower than that value for ANF-supported cata-lysts. According to TEM data, Ru particles on ANFC are larger than on ANF, but are more evenly distributed. An increase in the activity of the catalyst correlates with a change in the electronic state of the active component. XPS data for Ru indicate a shift in the binding energy towards lower values when going from ANF to ANFC.& COPY; 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Commercial cerium–zirconium oxide supports (Ce0.5Zr0.5O2, Ce0.75Zr0.25O2, and Ce0.4Zr0.5Y0.05La0.05O2) were used to prepare Ru/CeZrOx catalysts. According to the XRD and IR spectroscopy data, the supports consist of ceria-based substitutional solid solutions. The specific surface areas of supports and catalysts are similar and range from 71–89 m2/g. As shown by TEM and XRD methods, the size of support particles equals 6–11 nm. According to the TEM data, the size of ruthenium particles does not exceed 1.3 nm. The catalyst activity in the ammonia decomposition process was studied. The Ru/Ce0.75Zr0.25O2 catalyst at temperature 500 °C and GHSV 120,000 h−1 demonstrated the highest hydrogen productivity of 53.3 mmol H2/(gcat·min) and compares well with the best results reported in the literature. The kinetics of ammonia decomposition reaction were calculated using the Temkin–Pyzhov exponential expression. The developed mathematical model well described the experimental data. The studied catalysts demonstrated high activity for the ammonia decomposition reaction.

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 Pd 0.6 Ag 0.4 particles ( d av = 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 H 2 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.

An analytical equation for the rate of formation/consumption of nitrogen in the reversible reaction N2 + + 3H2 ↔ 2NH3 was obtained on the base of the analysis of the catalytic properties of 4%Ru–13.6%Cs/Sibunit and 4%Ru–5.4%Ba–7.9%Cs/Sibunit in the processes of ammonia decomposition (105 Pa; 350–470°C) and synthesis ammonia (6×105–5×106 Pa; 400–430°C). This equation allows one to describe correctly the dependence of the chemical reaction rate on the partial pressures of the components of the reaction mixtures for both forward and reverse reactions. The approach used to obtain the kinetic equation is based on the assumption that the adsorption sites on the ruthenium surface are initially filled with hydrogen and then replaced by nitrogen during competitive interaction. The values of the equilibrium constants and apparent activation energies for the synthesis and decomposition of ammonia on the 4%Ru–13.6%Cs/Sibunit and 4%Ru–5.4%Ba–7.9%Cs/Sibunit was found by using the proposed kinetic equation. The data are in good agreement with the ones presented in the literature.

The concepts of the effect of the adsorption of the reaction medium components on the selective hydrogenation of acetylene to ethylene under the action of supported palladium catalysts have been discussed. The role of interstitial solid solutions of carbon and hydrogen in palladium, which are formed upon contact of the catalyst with the reaction medium, in the occurrence of mass transfer processes between the surface and the subsurface layer of the active component has been shown. The ratio of activation barriers to ethylene desorption/adsorption processes, which determines the acetylene hydrogenation selectivity, can vary depending on the structure of palladium nanoparticles and the electronic state of Pd. In addition, changes in the electronic state affect the energy of the activated desorption of ethylene from palladium particles, and their structural features determine the energy of the activated adsorption and subsequent hydrogenation of ethylene to ethane.

The study of ruthenium catalysts for ammonia decomposition on carbonized and noncarbonized Al2O3 nanofibers (ANF) showed that activity of the catalysts with carbonized supports (ANFC) was twofold higher as compared to noncarbonized ones. Thus, on Ru/ANFC and Ru-Cs/ANFC the release of hydrogen reached 8.7 and 18.3 mmol H-2/(min.g(cat)), respectively, whereas on Ru/ANF and Ru-Cs/ANF, only 4.4 and 9.6 mmol H-2/(min.g(cat)), respectively. According to TEM, Ru particles on ANFC have a greater size than on ANF but are distributed more uniformly. As shown by TEM, XRD and XPS data, ANFC and ANF fibers are strongly different.

The conversion of methane–ethane, methane–ethylene, hydrogen–ethane, and hydrogen–ethylene mixtures on an electrically heated resistive fechral catalyst is studied. In the course of conversion, the catalyst surface is covered with graphite-like carbon deposits that have an additional catalytic effect resulting in the formation of C3 and C4 hydrocarbons. The latter are apparently formed with participation of ethylene formed from ethane. Hydrogen suppresses coking on the catalyst’s surface and reduces the yield of C3 and C4 hydrocarbons.

The effect of high-temperature treatment on the thermal stability of a graphitic carbon material Sibunit in an oxidizing medium was studied in dependence on the presence of active component – Pt, Pd or Ru. According to thermal analysis data, a high-temperature pretreatment of Sibunit increases the onset temperature of carbon oxidation. It was found that holding of the Ru/Sibunit samples for 4 h in a nitrogen: air (1 : 1) mixture at a temperature of 400 °С resulted in a partial destruction of the pyrocarbon matrix of Sibunit and increased the mean size of Ru particles. It was demonstrated that ruthenium catalysts can efficiently oxidize CO at a temperature not higher than 200 °С and withstand overheats up to 400 °С without a significant loss in activity.

This study investigates the co-conversion of methane and ethane in a T-shaped reactor over a resistive fechral catalyst heated to 1000°C. The feedstock consisted of two cold gas mixtures injected into the reactor separately: (1) 30 vol % CH4 + 70 vol % N2 (or N2 + O2); and (2) 30 vol % C2H6 + 70 vol % N2 (or N2 + O2). The simultaneous introduction of the methane–nitrogen and ethane–nitrogen mixtures into the reactor was found to enhance the selectivity of methane conversion to C3 hydrocarbons. This finding can be explained by the fact that the main reaction path involves interaction between the surface forms of methane and ethane stabilized in the carbon deposit layer on the surface of the resistive fechral catalyst. The article emphasizes the role of carbon deposits on the catalyst surface in the stabilization of CH3• radicals. These radicals are predominantly involved in oligomerization and polymerization reactions, including those in the presence of oxygen, due to the preferential occurrence of chain propagation reactions, rather than oxidation, because the major portion of the reaction mixture is at near room temperature.

A study on the effect of high-temperature treatment has on the thermal stability of Sibunit, a graphite-like carbon material, under the conditions of an oxidative environment depending on the presence of the active component (Pt, Pd or Ru) has been performed. Thermal analysis results show that preliminary high-temperature treatment of Sibunit raises the temperature of the onset of carbon oxidation. It is found that keeping Ru/Sibunit samples in a nitrogen–air mixture (1 : 1) for 4 h at a temperature of 400°C results in partial destruction of Sibunit’s pyrocarbon framework and an increase in the average size of Ru particles. Using Ru as an example, it is shown that ruthenium catalysts can effectively oxidize CO at temperatures no higher than 200°C and withstand overheating up to 400°C with no appreciable loss of activity.

The structural properties of Pd-Ga/gamma-Al2O3 samples prepared from joint Pd(NO3)(2) and Ga(NO3)(3) solution and their catalytic properties in liquid-phase acetylene hydrogenation have been studied. Using temperature programmed reduction (TPR-H-2), transmission electron microscopy (TEM), diffuse reflectance infrared Fourier transform spectroscopy of adsorbed CO (CO-DRIFTS) and X-ray photoelectron spectroscopy (XPS) it was found that an increase in the ethylene selectivity to similar to 66-70% is explained by the modification of the electronic properties of palladium by gallium at a Ga:Pd molar ratio of 0.5 and by the formation of bimetallic Pd2Ga particles in the case of Ga:Pd = 2.

The effect of the presence of the N-methyl-2-pyrrolidone (NMP) solvent, on the properties of Pd–Zn/Sibunit catalyst in hydrogenation of a gas mixture enriched in acetylene and hydrogen was studied. It was found that owing to selective solubility of alkanes and alkynes in the NMP medium and to the action of bimetallic Pd–Zn active sites, transformations of the formed C2H4 are efficiently suppressed, so that the ethylene selectivity reaches 85% at the acetylene conversion higher than 90%.. The effect of these factors levels off the modifying effect of carbon monoxide on the ethylene selectivity. Under the conditions of the liquid-phase reaction, the Pd–Zn/Sibunit catalyst demonstrates stable performance with the ethylene yield of 77%.

The present work is aim to study the adsorption/desorption properties of the Ag-modified Y zeolite towards toluene as well as its high temperature behavior under the prompt thermal aging conditions. The Ag/Y samples were obtained by an ion exchange technique and mixed with pure alumina used as a binder. The reference samples were prepared by an incipient wetness impregnation of alumina with a solution of silver nitrate and mixed with pure HY zeolite. The initial and aged samples were characterized by TEM and XRD methods. It was found that the Ag-modified Y zeolite strongly adsorbs toluene. Irreversible sorption of toluene over the most active silver sites was shown to exclude them from the participation in oxidation processes, thus diminishing the overall efficiency of the adsorption-catalytic system.

The effect of elevated temperatures on the textural and structural characteristics of the carbon material Sibunit in an oxygen-containing atmosphere was studied depending on the preliminary treatment of Sibunit with HNO 3 and the presence and the amount of an active component (Pt). According to the results of thermogravimetry, the preliminary treatment of Sibunit with HNO 3 led to an increase in the temperature range of carbon oxidation, while the introduction of Pt led to a decrease in this temperature range. It was found that an exposure of Pt/Sibunit samples for 4 h in a nitrogen–air mixture at a temperature of 400°C led to an increase in the total volume and average pore diameter with a slight change in the specific surface area, and the average particle size of platinum increased from 2 to 5 nm.

Ru-Cs(Ba)/Sibunit catalysts with the molar ratio Cs(Ba):Ru = 2.5 were synthesized using the carbon composite Sibunit calcined at 1400, 1600, 1800, 2000 and 2200 degrees C. Activity of the promoted catalysts in ammonia synthesis and their thermal stability to methanation were compared. Substantial changes in the structure and properties of Sibunit during its calcination were shown to affect the activity of the synthesized catalysts. As the calcination temperature was raised, specific surface (S-sp) decreased considerably, the carbon structure became ordered, whereas the specific activity (W-sp) increased. Thus, Wsp at 400 degrees C for Cs-Ru/Sib1400 was equal to 0.107 mol NH3.gRu(-1).h(-1), while for Cs-Ru/Sib2200 - 0.591 mol NH3.gRu(-1).h(-1). It was found that elevation of the calcination temperature and introduction of barium significantly enhanced thermal stability of the samples - the carbon loss decreased up to 10 times.