The Kinetics of Sorption of CO2 by Perovskite CaTiO3 and the Degree of Perovskite Decomposition with Nitric Acid after Its Mechanical Activation

The kinetics of mechanosorption of CO₂ by perovskite CaTiO₃ was analyzed. Data that characterized an increase in the reactivity of perovskite with respect to nitric acid caused by its mechanical activation in the atmosphere of carbon dioxide and in air were obtained.     

Mechanochemical interaction of alkali metal metasilicates with carbon dioxide: 1. Absorption of CO<Subscript>2</Subscript> and phase formation

Processes proceeding during the mechanochemical activation of alkali metal metasilicates M₂SiO₃ (where M is Li, Na, K) are studied in the air and in an atmosphere of carbon dioxide. At the initial stage of activation in a centrifugal planetary mill in an atmosphere of carbon dioxide, the main portion of supplied mechanical energy is expended for grinding and the mechanosorption of CO₂ occurs in the regime of cleavage, i.e., on the freshly formed surfaces of particles. As the time of activation increases, the specific surface area becomes constant, which, however, does not substantially affect the rate of interaction between carbon dioxide and silicates. The absorption of CO₂ occurs in the regime of friction on the active sites of already formed surfaces and is accompanied by the tribodiffusion of gas molecules into structurally disordered layers of particles. With identical amounts of supplied energy, the CO₂/M₂SiO₃ molar ratio in the samples activated in the medium of carbon dioxide increases in the Li < Na < K series. The main product of mechanically induced interactions between Li₂SiO₃ and CO₂ is the X-ray amorphous carbonate-silicate phase. In the case of sodium and potassium metasilicates, the reaction of mechanochemical substitution occurs to form corresponding carbonates, hydrocarbonates, and amorphous silica. It is shown that the character of mechanochemical interaction between M₂SiO₃ and CO₂ depends on the change in the Gibbs energy of the transformation of silicate into corresponding carbonate, as well as on the melting temperature and the hygroscopicity of silicate.     

Physicochemical processes in mechanical activation of titanium-and calcium-containing minerals

A comparative study of processes occurring in mechanical activation of perovskite, sphene, and vollastonite in air and in the atmosphere of carbon dioxide was made. Data on the effect of mechanical activation on the degree of perovskite and sphene decomposition by a 20% nitric acid solution under the standard conditions are presented. Original Russian Text A.M. Kalinkin, 2007, published in Zhurnal Prikladnoi Khimii, 2007, Vol. 80, No. 10, pp. 1585–1591.     

The mechanosorption of carbon dioxide by magnesium, calcium, and strontium metasilicates

Processes that occurred in the mechanical activation of MSiO₃ silicates (M = Mg, Ca, Sr) in a centrifugal planetary mill in the atmosphere of carbon dioxide (p(CO₂) = 10⁵ Pa) were comparatively studied. The interaction of carbon dioxide with silicates had the character of deep mechanosorption with massed penetration of gas molecules into the volume of particles and their “solution” in structurally disordered silicate matrices in the form of distorted CO₃²⁻ ions. No individual carbonate phases were formed. The absorbing ability of silicates with respect to carbon dioxide decreased in the series SrSiO₃ > CaSiO₃ > MgSiO₃. The carbon dioxide mechanosorption coefficients K _MS were calculated for Mg, Ca, and Sr silicates according to the earlier suggested kinetic model. A linear dependence of logK _MS on Δ_r G ₂₉₈^o for the transformation of silicates into the corresponding carbonates was observed.     

Calorimetric study of the component steps of oscillating chemical reactions

An influence of inorganic compounds (Fe₂O₃, ZnO, PbO, CaCO₃ and K₂CO₃) on the blast furnace coke thermal oxidation in the air and in the CO₂atmosphere was investigated by means of thermal analysis. A catalytic effect showed itself at the oxidation in the air, especially with PbO and K₂CO₃. These compounds bring the oxidation starting temperature and activation energy down and increase the reaction rate constant most distinctly. The PbO and K₂CO₃ actions differ in their mechanisms. K₂CO₃ accelerates particularly the amorphous coke fractions oxidation. In the CO₂ atmosphere an important catalytic effect occurred only with K₂CO₃. The PbO catalytic influence is less distinct. This revised version was published online in July 2006 with corrections to the Cover Date.     

Zur Reaktion von Silber mit Kohlendioxid

On the Reaction of Silver with Carbon Dioxide Mechanical activation of metallic silver in a CO₂ atmosphere was shown to oxidize the silver. The resulting monovalent silver was found by a wet chemical procedure to be made up of Ag⁺ ions, while the Ag₂CO₃ was determined from Debye-Scherrer patterns. During mechanical treatment CO₂ and the CO formed are absorbed within the solid. The reaction equation 2 Ag + 2 CO₂ ← Ag₂CO₃ + CO is suggested for the reaction, giving a positive free enthalpy of 212 kJ/mol. This high amount of energy is locally supplied during the mechanical treatment of the metallic silver.     

Sorption and Textural Properties of Activated Carbon Derived from Charred Beech Wood

The aim of this study was to prepare activated carbon materials with different porous structures. For this purpose, the biomass precursor, beech wood, was carbonized in an inert atmosphere, and the obtained charcoal was physically activated using carbon dioxide at 1273 K. Different porous structures were obtained by controlling the time of the activation process. Prepared materials were characterized in terms of textural (N₂ sorption at 77 K), structural (XRD), and sorption properties (CO₂, C₂H₄, C₄H₁₀). The shortest activation time resulted in a mostly microporous structure, which provided a high sorption of CO₂. Increasing the activation time led to an increasing of the pores’ diameters. Therefore, the highest ethene uptake was obtained for the material with an intermediate activation time, while the highest butane uptake was obtained for the material with the highest activation time.     

Kinetics of carbon dioxide mechanosorption by Ca-containing silicates

Kinetics of mechanically induced CO₂ extensive sorption by silicate minerals (labradorite, diopside, okermanite, ghelenite and wollastonite) was considered. Mechanical activation of the silicates was carried out in a planetary mill in CO₂ at atmospheric pressure. Carbon dioxide was consumed by the silicates in the form of carbonate ions and its content in the samples after 30 min of mechanical treatment reached 3–12 mass% CO₂ depending on mineral composition. Equations that reasonably good represent kinetics of CO₂ mechanosorption by silicates were proposed. These equations enable to calculate mechanosorption coefficients that characterize the diffusivity of CO₂ into disordered silicate matrix under intensive mechanical impact. Thermal analysis of the mechanically activated silicates showed that there was positive correlation between temperature of complete carbonate decomposition and mechanosorption coefficient.     

Atomic-Scale Insight into Exsolution of CoFe Alloy Nanoparticles in La0.4Sr0.6Co0.2Fe0.7Mo0.1O3−δ with Efficient CO2 Electrolysis

In situ exsolution of metal nanoparticles in perovskite under reducing atmosphere is employed to generate a highly active metal–oxide interface for CO₂ electrolysis in a solid oxide electrolysis cell. Atomic-scale insight is provided into the exsolution of CoFe alloy nanoparticles in La_0.4Sr_0.6Co_0.2Fe_0.7Mo_0.1O_3−δ (LSCFM) by in situ scanning transmission electron microscopy (STEM) with energy-dispersive X-ray spectroscopy and DFT calculations. The doped Mo atoms occupy B sites of LSCFM, which increases the segregation energy of Co and Fe ions at B sites and improves the structural stability of LSCFM under a reducing atmosphere. In situ STEM measurements visualized sequential exsolution of Co and Fe ions, formation of CoFe alloy nanoparticles, and reversible exsolution and dissolution of CoFe alloy nanoparticles in LSCFM. The metal–oxide interface improves CO₂ adsorption and activation, showing a higher CO₂ electrolysis performance than the LSCFM counterparts.     

A study of the electrical conductivity and transition points of sodium carbonate

The electrical conductivity of Na₂CO₃ has been measured between 270 and 830°C under different atmospheres: air, argon, nitrogen, and carbon dioxide. The conductivity depends on atmosphere owing to superficial decomposition of Na₂CO₃. The existence of a thermal transformation at 620°C seems confirmed. The determination of the transport numbers shows that cations only are responsible for the current. From measurements taken on samples containing traces of CaCO₃, the migration energy of cation vacancies is inferred.     

Atomic‐Scale Insight into Exsolution of CoFe Alloy Nanoparticles in La0.4Sr0.6Co0.2Fe0.7Mo0.1O3−δ with Efficient CO2 Electrolysis

In situ exsolution of metal nanoparticles in perovskite under reducing atmosphere is employed to generate a highly active metal–oxide interface for CO₂ electrolysis in a solid oxide electrolysis cell. Atomic‐scale insight is provided into the exsolution of CoFe alloy nanoparticles in La_0.4Sr_0.6Co_0.2Fe_0.7Mo_0.1O_3?δ (LSCFM) by in situ scanning transmission electron microscopy (STEM) with energy‐dispersive X‐ray spectroscopy and DFT calculations. The doped Mo atoms occupy B sites of LSCFM, which increases the segregation energy of Co and Fe ions at B sites and improves the structural stability of LSCFM under a reducing atmosphere. In situ STEM measurements visualized sequential exsolution of Co and Fe ions, formation of CoFe alloy nanoparticles, and reversible exsolution and dissolution of CoFe alloy nanoparticles in LSCFM. The metal–oxide interface improves CO₂ adsorption and activation, showing a higher CO₂ electrolysis performance than the LSCFM counterparts.     

Aromaticity‐promoted CO2 Capture by P/N‐Based Frustrated Lewis Pairs: A Theoretical Study

Carbon dioxide (CO₂, a common combustion pollutant) releasing continuously into the atmosphere is primarily responsible for the rising atmospheric temperature. Therefore, CO₂ sequestration has been an indispensable area of research for the past several decades. On the other hand, the concept of aromaticity is often employed in designing chemical reactions and metal‐free frustrated Lewis pairs (FLPs) have proved ideal reagents to achieve CO₂ reduction. However, considering FLP and aromaticity together is less developed in CO₂ capture. Here we report theoretical investigations on the aromaticity‐promoted CO₂ activation, involving heterocyclopentadiene‐bridged P/N‐FLPs. The calculations reveal that furan‐ and pyrrole‐bridged P/N‐FLPs can make CO₂ capture both thermodynamically and kinetically favorable (with activation energies of 5.4–7.7 kcal mol^?1) due to the aromatic stabilization of the transition states and products. Our findings could open an avenue to the design of novel FLPs for CO₂ capture.     

Application of DTA-TG-MS for determination of chemical stability of BaCeO3−δ-based protonic conductors

Thermogravimetry (TG) and Differential Thermal Analysis (DTA) techniques coupled with mass spectrometry were applied to evaluate the chemical stability of BaCeO_3?δ-based materials in the CO₂- and H₂O-rich atmosphere. The different groups of materials were investigated: solid solutions of BaCeO₃–BaTiO₃ and BaCeO₃–BaSnO₃ acceptor doped by Y or In and composite materials with nominal composition (1?x)BaCe_0.9Y_0.1O_3?δ-xYPO₄. To evaluate the chemical stability towards carbon dioxide and water vapour samples were exposed to atmosphere containing CO₂/H₂O (7 % of CO₂ in air, 100 % RH) at temperature of 25 °C for 350 h. Thermal analysis (TG/DTA) was applied to analyse the materials before and after the test. To support the interpretation of TG/DTA results, the analysis of gaseous products evoluted during thermal treatment of the samples was provided using mass spectrometer. This combined analysis clearly shows that during the exposition test, the conversion of barium cerate to barium carbonate and barium hydroxide occurs. The amount of BaCO₃ and the degree of BaCeO_3?δ conversion depend on the type of barium cerate modification. The mass loss observed after the exposition test can be treated as a measure of chemical instability of BaCeO_3?δ-based materials. The correlation of chemical stability, described by the mass loss, on Goldschmidt tolerance factor, describing the deviation from ideal perovskite structure, was found in most of the materials investigated. However, the influence of the microstructure and the modification the grain boundaries on the chemical stability of BaCeO_3?δ-based materials cannot be neglected.     

Properties of internal heat supply with carbon dioxide reforming of methane over a Ni/Al2O3 catalyst.

An addition of 6%-oxygen into a reactant of CH₄/CO₂(1/1) gave lower operating temperature of carbon dioxide reforming of methane by 130 K in obtaining 0.029 MPa of H₂, accompanied by a more endothermic atmosphere in the catalyst bed than in the absence of oxygen. This revised version was published online in June 2006 with corrections to the Cover Date.     

Molecular dynamic simulations of carbon nanotubes in CO2 atmosphere

This work investigates by means of molecular dynamics the filling of carbon nanotubes by carbon dioxide molecules. Nanotubes of various sizes are simulated and the resulting CO₂ density calculated. The effects of various CO₂ models are also investigated. The results show that the carbon dioxide molecules have a natural tendency to fill the nanotubes and the final CO₂ concentration inside the nanotube can be approximately 100 times (depending on diameter and CO₂ model) higher than that of the external atmosphere.     

Role of reaction atmosphere in preparation of potassium tantalate through sol–gel method

Potassium tantalate (KT) thin films and powders of both K₂Ta₂O₆ (KT pyrochlore) and KTaO₃ (KT perovskite) structures were prepared by means of chemical solution deposition method using Si(111) with ZnO and MgO buffer layers as a substrate. The influence of reaction atmosphere on reaction pathway and phase composition for both KT powders, and KT thin films has been studied mainly by means of powder diffraction and infrared spectroscopy. When an oxygen flow instead of static air atmosphere has been used the process of pyrolysis in oxygen runs over much narrower temperature interval (200–300 °C), relatively to air atmosphere (200–600 °C) and almost no (in case of powders), or no (in case of thin films) pyrochlore intermediate phase has been detected in comparison with treatment in air, where the pyrochlore phase is stable at temperatures 500–600 °C (powders). KT perovskite phase starts to crystallize at temperatures 50° and 150 °C lower compared to air atmosphere in case of powders and thin films, respectively. Microstructure formed by near-columnar grains and small grains of equiaxed shape was observed in films treated in oxygen and air atmosphere, respectively.     

Preparation and characterization of activated carbon from cotton stalks in a two-stage process

Activated carbons are prepared from cotton stalks by chemical activation with ZnCl₂, H₂SO₄ and physical activation using CO₂ and steam-CO₂ mixture for temperatures of 750, 850 and 900 °C. The effects of activation temperature and duration time, impregnation concentration of agent, impregnation times, and physical activating agent are examined. These materials are characterized by adsorption/desorption of N₂ to determine the BET areas, thermogravimetric analysis (TG, DTA), FTIR and scanning electron microscopy (SEM). ZnCl₂ under CO₂ atmosphere was found more effective than H₂SO₄ as a chemical reagent under identical conditions in terms of porosity development. The maximum BET surface area is found to be 2053 m²/g for active carbons produced with ZnCl₂ activation under CO₂ atmosphere.     

Preparation of activated carbon from cherry stones by physical activation in air. Influence of the chemical carbonisation with H2SO4

In the preparation of activated carbon (AC) by the method of physical activation, the carbonisation stage is usually carried out by heat treatment of a precursor at a given temperature in an inert atmosphere, whereas the activation stage is performed in air, carbon dioxide or steam atmosphere. Here, the use of a chemical carbonisation-based method with H₂SO₄ in aqueous solution as an alternative to the physical carbonisation method is studied. Using cherry stones (CS), AC was prepared by physical activation in air, as usual, and by carbonising with H₂SO₄ prior to activating in air. CS was carbonised at 600 °C in nitrogen atmosphere or with H₂SO₄ solutions of various concentrations and the resulting products were activated at 350–550 °C in air. Characterisation was undertaken by proximate analysis, TG–DTG analysis, N₂ adsorption at −196 °C, mercury porosimetry, density measurements and FT-IR spectroscopy. By the H₂SO₄-chemical carbonisation, AC with a lower inorganic matter content, wider pore size distribution in the meso- and macropore ranges, higher mesopore volume and carboxylic acid groups are prepared. The development of microporosity is similar regardless of the carbonisation method provided that the activation of the chemically carbonised product is effected at higher temperature. Physical carbonisation results in AC with an homogeneous macroporosity and with quinone type functional groups. Yield is also slightly higher by this carbonisation method.     

A Microwave-Assisted Boudouard Reaction: A Highly Effective Reduction of the Greenhouse Gas CO2 to Useful CO Feedstock with Semi-Coke

The conversion of CO₂ into more synthetically flexible CO is an effective and potential method for CO₂ remediation, utilization and carbon emission reduction. In this paper, the reaction of carbon-carbon dioxide (the Boudouard reaction) was performed in a microwave fixed bed reactor using semi-coke (SC) as both the microwave absorber and reactant and was systematically compared with that heated in a conventional thermal field. The effects of the heating source, SC particle size, CO₂ flow rate and additives on CO₂ conversion and CO output were investigated. By microwave heating (MWH), CO₂ conversion reached more than 99% while by conventional heating (CH), the maximum conversion of CO₂ was approximately 29% at 900 °C. Meanwhile, for the reaction with 5 wt% barium carbonate added as a promoter, the reaction temperature was significantly reduced to 750 °C with an almost quantitative conversion of CO₂. Further kinetic calculations showed that the apparent activation energy of the reaction under microwave heating was 46.3 kJ/mol, which was only one-third of that observed under conventional heating. The microwave-assisted Boudouard reaction with catalytic barium carbonate is a promising method for carbon dioxide utilization.     

Ambient Air Temperature Assisted Crystallization for Inorganic CsPbI2Br Perovskite Solar Cells

Inorganic cesium lead halide perovskites, as alternative light absorbers for organic–inorganic hybrid perovskite solar cells, have attracted more and more attention due to their superb thermal stability for photovoltaic applications. However, the humid air instability of CsPbI₂Br perovskite solar cells (PSCs) hinders their further development. The optoelectronic properties of CsPbI₂Br films are closely related to the quality of films, so preparing high-quality perovskite films is crucial for fabricating high-performance PSCs. For the first time, we demonstrate that the regulation of ambient temperature of the dry air in the glovebox is able to control the growth of CsPbI₂Br crystals and further optimize the morphology of CsPbI₂Br film. Through controlling the ambient air temperature assisted crystallization, high-quality CsPbI₂Br films are obtained, with advantages such as larger crystalline grains, negligible crystal boundaries, absence of pinholes, lower defect density, and faster carrier mobility. Accordingly, the PSCs based on as-prepared CsPbI₂Br film achieve a power conversion efficiency of 15.5% (the maximum stabilized power output of 15.02%). Moreover, the optimized CsPbI₂Br films show excellent robustness against moisture and oxygen and maintain the photovoltaic dark phase after 3 h aging in an air atmosphere at room temperature and 35% relative humidity (R.H.). In comparison, the pristine films are completely converted to the yellow phase in 1.5 h.