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The efficiency of CO2 methanation was estimated through gas chromatography in the presence of Co–Fe catalysts. Scanning electron microscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, and Mossbauer spectroscopy were applied for ex-situ analysis of the catalysts after their test in the methanation reaction. Thermal programmed desorption mass spectroscopy experiments were performed to identify gaseous species adsorbed at the catalyst surface. Based on the experimental results, surface reaction model of CO2 methanation on Co–Fe catalysts was proposed to specify active ensemble of metallic atoms at the catalyst surface, orientation of adsorbed CO2 molecule on the ensemble and detailed reaction mechanism of CO2→CH4 conversion. The reaction step when OH group in the FeOOH complex recombined with the H atom adsorbed at the active ensemble to form H2O molecule was considered as the rate-limiting step.

For effective carbon dioxide (CO2) methanation, bimetallic Co80Ni20/CNTs, Ni80Fe20/CNTs, and Co93Fe07/CNTs nanocomposite catalysts, where subscript numbers indicate the metal content (wt.%), have b...

Bromination of activated carbon GSGD was performed and active bromine-containing precursors were obtained, in which bromine is capable of being replaced by sulfur-containing functional groups. Bromination with liquid bromine and a solution of bromine in potassium bromide at room temperature leads to the introduction of 0.44–0.45 mmol g–1 of bromine into the surface layer of activated carbon. The treatment of brominated samples with sulfur-containing reagents with subsequent oxidation allows obtaining carbon samples that are catalytically active in the dehydration reaction of isopropyl alcohol in a gas phase. The temperature of complete conversion of isopropyl alcohol to propylene is a measure of catalytic activity. The concentration of sulfogroups in the prepared samples is up to 0.3 mol g–1. Thermogravimetry and thermoprogrammed desorption with mass spectrometric registration of products were used to study the thermal stability of modified activated carbon samples. The influence of the nature of brominating reagents, hydrolysis conditions and oxidation conditions on the structure, surface concentration of grafted S-containing groups and catalytic properties of the obtained materials was studied. Pre-bromination leads to an increase in the catalytic activity of activated carbon modified with sulfur-containing groups and the temperature of complete conversion of isopropyl alcohol to propylene decreases up to 400C depending on the concentration of sulfogroups.

In this chapter, we consider bromination with KBr3 and Br2 to prepare precursors to sulfonated nanoporous activated carbons (NACs). Sulfonated NACs were prepared and characterized by N2 adsorption, TGA, TPD MS, TPD IR, elemental analysis, and also using SEM, TEM, HRTEM, and SAED. The majority of sulfonated NACs are efficient catalysts for the 2-propanol dehydration to propylene. However, they showed a significant difference in the temperature at 50 and 100% conversion of 2-propanol to propylene. These parameters depend on the bromination method, surface chemistry, and used NACs. The best catalytic performance was found for the sulfonated NACs covered with carboxylic groups and prepared by pre-bromination with Br2.

The production of propylene by dehydration of 2-propanol at solid-vapor interfaces, as an example of the acidcatalyzed surface reaction, was explored by using sulfonated polyacrylonitrile-derived activated carbon fibers (PAN-ACFs). To prepare these catalysts, the PAN-ACFs obtained by onestep carbonation-activation were modified with a surface coverage of high acidity. The surface of PAN-ACFs was sulfurated with sulfur vapors at high temperatures followed by oxidation, to yield the corresponding sulfonates. The chemical analysis showed that the carbon surface layer contains from 1.28 to 6.10 mmol$\mathrm{g}^{-1}$ of sulfur, including the contribution of sulfonic $(\mathrm{S}\mathrm{O}{}_{3}\mathrm{H})$ groups. In addition to sulfonic groups, the obtained catalysts contain carboxyl, lactone, and phenolic groups, which are formed as a result of oxidation treatment. In order to understand the changes in surface chemistry and the results of sulfuration and oxidation, the sulfonated PAN-ACFs were characterized by a variety of techniques including TPD MS, TGA, SEM, and FTIR ATR. During a typical temperature mode screening at catalyst testing, it was found that the sulfonated PAN-ACFs prepared by treatment with sulfur vapor at low temperature, at $400\circ \mathrm{c}$ and $500\circ \mathrm{c}$, are very efficient at dehydrating 2-propanol. A weighed mass of 100 mg of each of these catalysts was operated at 165-175°C in 12 hours, and the catalysts were characterized by high conversion of 2-propanol and high selectivity to propylene, with a propylene yield of about 100%. Furthermore, the solid acid catalysts have high stability and strong acidity and can be reused with no significant loss in the activity after the third cycle in the subsequent 20 cycles. The preparation of solid acid catalysts from PAN-ACFs affords a novel strategy for producing propylene through alternative green and sustainable technologies.

Fluorination of nanoporous activated carbon and its subsequent modification with sodium sulfide, which leads to the introduction of sulfur-containing groups in the carbon matrix containing fluorine, was carried out. After oxidation with hydrogen peroxide, sulfo groups are formed in the surface layer of activated carbon, i.e., in this way, it is possible to obtain samples that have both fluorine-and sulfur-containing functional groups. As a result of this work, active and stable catalysts of the reactions catalyzed by acids were obtained. They have a fairly high catalytic activity and thermal stability. When testing the obtained samples in the temperature range up to 250°C under the catalytic 2-propanol dehydration, the yield of propylene remains unchanged for each cycle, the temperature of the dehydration reaction does not change, the activity remains stable for at the least three catalysis cycles, with no deactivation of catalysts.

Based on the data of the thermoprogrammed desorption and using mass-spectroscopic analysis of desorbed products and on the kinetic patterns of the methanation process for cobalt–nickel catalysts, we suggested a mechanism for the reaction which passes through forming intermediate formyl compounds: CHO*, HCOH*, and HCOOH*. Because of the high stability of the carbon dioxide molecule, the step of adding the first hydrogen atom is the limiting step. Such a mechanism is in good agreement with the proposed kinetic equations.

Nickel sensor action for analytical detection of hydrogen and oxygen gases is dependent on the adsorption, dissociation, and diffusion of hydrogen and oxygen. These processes and water adsorption was studied by the density functional theory with model Ni(111) slabs. It was found that H atoms were absorbed only by voids in the fcc structure as the Ni surface was filled. The voids in the fcc sites were also preferred for the adsorption of oxygen atoms and oxygen-hydrogen pairs. Two bridge adsorption forms of water were found in addition to the well-known, top-site adsorption form.

Here we compared the results of density functional theory (DFT) modeling of adsorption on Ni-Fe(111) model surface and thermoprogrammed desorption studies of species adsorbed onto Ni-Fe catalysts during hydrogenation of the carbon dioxide (CO 2 ). The DFT study showed that Fe atoms are not clustered in an environment of Ni atoms and are situated randomly far from each other. We have shown that CO 2 adsorbs slightly stronger on the Ni-Fe alloy than on pure nickel. We suggest that the optimal composition of bimetallic Ni-Fe catalysts should be about 8–10 at% of Fe in Ni. This statement is confirmed by our experimental data on the thermodesorption and catalytic activity of the Ni-Fe alloys in the methanation reaction. According to the data of thermal programmed desorption mass spectroscopy, the CO 2 molecule adsorbed on the surface of the Ni 75 Fe 25 and Ni 80 Fe 20 catalysts splits into CO* and O*. Resulting strongly chemisorbed CO prevents further hydrogenation reactions on the surface of the catalyst. The modeling does not answer the question of how iron influences the methanation reaction activity and selectivity.

Bromination and oxidation are concurrent reactions that passed on the surface of carbon solids and carbon nanomaterials. In this study, their products were modeled for a hexagonal carbon network that forming a honeycomb 2D planar structure made of sp2-hybridized bonded carbon. Two types of active centers, namely, HC=CH and C-H groups linked to peripheral zigzag carbon atoms, were considered during the DFT simulations. The oxidation process is more advantageous than bromination. Free active centers, even that on the oxidized surface, maintain their ability to the bromine addition reaction. However, the probability of their existence on the oxidized surface is very low. The active centers of the surface can be renewed by the removal of oxygen-containing groups at thermal treatment in an inert atmosphere.

Here we report on the phosphorylation of activated carbon (AC) at 500–800 °C. From thermal, titrimetric, and catalytic data, high surface acidity of the prepared solids is attributed to the total concentration of the protogenic groups. Transmission electron microscopy and nitrogen physisorption measurements showed a chemisorption-induced contraction of microporosity. The most active catalysts prepared at 700 °C contain 1.04 mmol g−1 of the phosphonic groups and supports dehydration of isopropanol with about 100% conversion and 100% selectivity to propylene at 170–180 °C.

Here we report on the preparation of effective aminated sorbents based on activated carbon (AC), which was produced from natural raw material (Apricot pits) for the removal of heavy metal ions from wastewaters. For effective functionalization, bromination and following amination were carried out. At the amination stage, the grafted bromine groups were substituted by amino groups. Amination by ethylenediamine and monoethanolamine alcohol solutions can replace 0.52 mmol of bromine groups by 0.51–0.57 mmol of amino groups per gram of sorbent. We showed that the aminated ACs could remove 90% of Cu(II) ions from aqueous solutions containing from 4×10−5 to 1×10−3 mol/L of Cu2+. The regeneration of used sorbents and the recovery of copper were also studied to evaluate the reusability of the sorbents.

In this work, we evaluated the reasons of the high reactivity of carbon surface in the bromination reaction. For this purpose, the active centers of carbons were simulated within the density functional theory method. It was shown that all proposed models derived from the honeycomb structure of coronene have edge double C=C bond as an active center of the surface. With an increase in the size of the carbon models, such bonds become shorter, this increases the bond order and, simultaneously, the affinity for the addition reactions becomes significant. The symmetry of models, the defects of the structure or vacancies of carbon atoms do not effect on the length of the edge double C=C bonds. We calculated the reaction thermodynamic for the interaction of C 54 H 18 cluster with dibromine. At these processes, the functional oxygen-containing groups have a certain impact only on the nearest neighboring carbon bonding. The calculation showed that the bromine molecules attack the edge double C=C bond. This way is more energetically favorable than the substitution of hydrogen for bromine.