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

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 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 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.

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 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.

It is shown that treatment of Sibunit at 2200 degrees C leads to a full restructuring of the structural and textural parameters of the carbon support. The structure of Sibunit becomes more ordered - according to the XRD, the interplanar distance d(002) decreases by 0.005 nm compared to the original Sibunit; according to the Raman spectroscopy, I-D/I-G decreases from 1.59 to 1.18 and the 2D-line increases significantly. The specific surface area of Sibunit after heat treatment decreases from 303 to 29 m(2)/g, the total pore volume decreases by 2 times, and the pore diameter increases by 4 times. The dependence of the specific activity on the amount of the active component is extreme, and the maximum for the 1%Ru-3.4%Cs/Sib2200 catalyst and is 1.52 mol NH3/g(Ru)*h.

This work presents results of XAFS study of the local structure and state of rutenium in the active component of low-percentage model metal-carbon catalysts for the low temperature synthesis/decomposition of ammonia. All XAFS spectra (Ru-K edge) of the initial and reduced samples studied were recorded at the Siberian Synchrotron and Terahertz Radiation Center (SSTRC, Novosibirsk). The structural parameters and phase composition of samples of different pre-histories were determined. The obtained information about Ru/C nanosystem can provide an optimal direction for the development of preparation methods for creating nanocomposite (platinoid - carbon) supported catalysts with desired properties. Perspectives of the used approach were shown.

The interaction between the components of a Ru–Rb/Sibunit catalyst for the decomposition of ammonia is studied via XAFS spectroscopy, X-ray diffraction with synchrotron radiation, and high-resolution transmission electron microscopy. The porous structure of the samples is examined at the stages of preparation. A set of measures reveals the presence of ruthenium in the catalyst (mainly in the metallic state) and the absence of joint phases of ruthenium and rubidium. It is found that rubidium is in an oxidized state in the catalyst in the form of compounds in direct contact with particles of active component and comparable in size to the latter, and as small clusters found mainly in the structure of carbon support.

In the present work, adsorptive-catalytic properties and thermal stability of the systems based on ZSM-5 zeolite and γ-Al2O3, used as a binder, were studied. The zeolite was modified with silver, and the Ag loading used was 5 and 10 wt%. Characterization of the samples by a transmission electron microscopy has revealed that for the 5%Ag/ZSM-5 sample the predominant part of silver is represented by ion-exchanged forms. The 10%Ag/ZSM-5 sample contains also silver nanoparticles and clusters on the outer zeolite surface. As it was found by means of X-ray diffraction analysis, all these surface Ag species are roentgen-amorphous. Diffuse reflectance UV–vis spectroscopy confirms presence of the surface Ag clusters, which concentration increases after the high-temperature aging. The adsorption capacity of the samples was estimated using toluene as a model aromatic compound. The composition of the reaction mixture during the aging procedures was varied in order to elucidate the contribution of different silver sites to hydrocarbons sorption, their partial oxidation and oxidation of carbon monoxide.

In the present research, the adsorption-desorption properties of the ZSM-23 zeolite (SiO2/Al2O3 ratio of 100) with respect to toluene used as a model adsorbate were examined. Both the pristine and Ag-modified samples were studied using specially designed installation and technique allowing quantitative determination of the weakly and strongly bounded toluene species, which desorb within the ranges of 100-200 and 200-400 °C, respectively. Thermal stability of the samples along with the catalytic activity in oxidation of CO and hydrocarbons was investigated in a prompt thermal aging regime. It was found that toluene adsorbs predominantly on the outer surface of the zeolite, and the contribution of its inner porous structure into the adsorption process is negligible. Modification of the zeolite with silver was shown to improve the adsorption properties noticeably. Thus, the amount of strongly bounded toluene is increased by 1.8 times. At the same time, introduction of silver has a drawback connected with destruction of the zeolite structure. Moreover, after the prompt thermal aging the silver particles were mainly found to be agglomerated and coated by silica released from the zeolite lattice. Additionally, the part of silver species was found on alumina used a binder, thus testifying towards silver migration from one oxide support to another.In the present research, the adsorption-desorption properties of the ZSM-23 zeolite (SiO2/Al2O3 ratio of 100) with respect to toluene used as a model adsorbate were examined. Both the pristine and Ag-modified samples were studied using specially designed installation and technique allowing quantitative determination of the weakly and strongly bounded toluene species, which desorb within the ranges of 100-200 and 200-400 °C, respectively. Thermal stability of the samples along with the catalytic activity in oxidation of CO and hydrocarbons was investigated in a prompt thermal aging regime. It was found that toluene adsorbs predominantly on the outer surface of the zeolite, and the contribution of its inner porous structure into the adsorption process is negligible. Modification of the zeolite with silver was shown to improve the adsorption properties noticeably. Thus, the amount of strongly bounded toluene is increased by 1.8 times. At the same time, introduction of silver has a drawback connected with des...

Three-component Ru-Ba-Cs/C catalysts supported on the graphite-like carbonaceous composite material Sibunit were synthesized. The effects of the graphitization procedure of the support (thermal treatment at 1900 °C) on the phase composition and the distribution of the components were studied. The catalytic activity in the ammonia decomposition reaction and the thermal stability of the samples were examined in comparison with the untreated support. The samples were characterized by Raman spectroscopy, XAFS, TEM, and XRD methods. It was found that in the case of untreated support, Ru presents in the form of both the metallic and partially oxidized fine particles. The graphitization of the carbon support facilitates the formation of large, well-crystallized metal particles. Barium in both samples was found to be unevenly distributed and presented mainly as large particles of carbonate. Cesium-containing species were not detected. The effect of the support graphitization on the thermal stability is comparable with catalyst modification by Ba and Cs. At the same time, combination of these effects noticeably increases the efficiency of the catalyst. Thus, the non-promoted Ru catalyst deposited on the untreated support decomposes 107 g of NH3 per 1 g of the lost carbon. Modification of the catalyst with Ba and Cs allows one to increase this value up to 498 g of NH3, while graphitization of the support and application of the combined approach were shown to give 910 and 1577 g, correspondingly.

The effect of high-temperature (1400-2200 degrees C) treatment of the carbon material Sibunit on its structural properties was studied. High-temperature treatment leads to structural ordering of the initial Sibunit. As a result of preliminary graphitization, specific surface area decreases by a factor of 10, but thermal stability increases. A good correlation between XRD, Raman spectroscopy and TGA data is observed. For the Sibunit sample treated at 2200 degrees C, the interplanar distance d(002) estimated by XRD decreases by 0.05 A in comparison with the initial Sibunit, ID/IG decreases from 1.59 to 1.18, and the 2D line substantially increases, which testify to the structural ordering. According to TGA, the temperatures corresponding to the onset of oxidation, 50% oxidation and the end of oxidation of Sibunit calcined at 2200 degrees C are synchronously shifted by 100 degrees C with respect to the initial Sibunit.

Ru-K/Sibunit catalysts with different molar ratio of promotor and active component were studied in the low-temperature synthesis and decomposition of ammonia. It was shown that activity of the catalysts in the synthesis reaction increases with the molar ratio of potassium and ruthenium: 0.087 and 0.397 mmol NH3/gcat*h for K/Ru = 0.5 and 2.5, respectively, at a temperature of 350 C, whereas in the decomposition reaction the activity decreases and is equal to 349.2 and 73.8 mmol NH3/gcat*h, respectively, for K/Ru = 0.5 and 2.5 at 450 C.

The interaction of platinum with carbonaceous graphite-like material Sibunit was studied. It was found that carbon covers the platinum particles during the reduction in a hydrogen flow. Chemisorption of CO over such samples has shown that just a small part of Pt surface is opened and accessible for the reagents. The carbon support was additionally pretreated by a high temperature graphitization in nitrogen. The amount of surface oxygen-containing groups was increased by a treatment with nitric acid. An examination of the Pt-loaded samples in hydrogen has revealed that the oxidative treatment does not affect the activity in the carbon hydrogenation process. Both the initial and oxidized Pt-loaded samples facilitate intensive carbon interaction with hydrogen leading to quite similar amounts of methane released. Contrary, the graphitization of the support allows one to minimize the methane formation. Lower specific surface area and absence of amorphous carbon weaken the platinum–carbon interaction and facilitate the formation of larger particles, thus complicating the realization of hydrogenation mechanism.