Effects of the Crystalline Properties of Hollow Ceria Nanostructures on a CuO-CeO2 Catalyst in CO Oxidation

The development of an efficient and economic catalyst with high catalytic performance is always challenging. In this study, we report the synthesis of hollow CeO₂ nanostructures and the crystallinity control of a CeO₂ layer used as a support material for a CuO-CeO₂ catalyst in CO oxidation. The hollow CeO₂ nanostructures were synthesized using a simple hydrothermal method. The crystallinity of the hollow CeO₂ shell layer was controlled through thermal treatment at various temperatures. The crystallinity of hollow CeO₂ was enhanced by increasing the calcination temperature, but both porosity and surface area decreased, showing an opposite trend to that of crystallinity. The crystallinity of hollow CeO₂ significantly influenced both the characteristics and the catalytic performance of the corresponding hollow CuO-CeO₂ (H-Cu-CeO₂) catalysts. The degree of oxygen vacancy significantly decreased with the calcination temperature. H-Cu-CeO₂ (HT), which presented the lowest CeO₂ crystallinity, not only had a high degree of oxygen vacancy but also showed well-dispersed CuO species, while H-Cu-CeO₂ (800), with well-developed crystallinity, showed low CuO dispersion. The H-Cu-CeO₂ (HT) catalyst exhibited significantly enhanced catalytic activity and stability. In this study, we systemically analyzed the characteristics and catalyst performance of hollow CeO₂ samples and the corresponding hollow CuO-CeO₂ catalysts.     

Catalysts for the Conversion of CO2 to Low Molecular Weight Olefins—A Review

There is a large worldwide demand for light olefins (C₂⁼–C₄⁼), which are needed for the production of high value-added chemicals and plastics. Light olefins can be produced by petroleum processing, direct/indirect conversion of synthesis gas (CO + H₂) and hydrogenation of CO₂. Among these methods, catalytic hydrogenation of CO₂ is the most recently studied because it could contribute to alleviating CO₂ emissions into the atmosphere. However, due to thermodynamic reasons, the design of catalysts for the selective production of light olefins from CO₂ presents different challenges. In this regard, the recent progress in the synthesis of nanomaterials with well-controlled morphologies and active phase dispersion has opened new perspectives for the production of light olefins. In this review, recent advances in catalyst design are presented, with emphasis on catalysts operating through the modified Fischer–Tropsch pathway. The advantages and disadvantages of olefin production from CO₂ via CO or methanol-mediated reaction routes were analyzed, as well as the prospects for the design of a single catalyst for direct olefin production. Conclusions were drawn on the prospect of a new catalyst design for the production of light olefins from CO₂.     

Improved Methane Production by Photocatalytic CO2 Conversion over Ag/In2O3/TiO2 Heterojunctions

In this work, the role of In₂O₃ in a heterojunction with TiO₂ is studied as a way of increasing the photocatalytic activity for gas-phase CO₂ reduction using water as the electron donor and UV irradiation. Depending on the nature of the employed In₂O₃, different behaviors appear. Thus, with the high crystallite sizes of commercial In₂O₃, the activity is improved with respect to TiO₂, with modest improvements in the selectivity to methane. On the other hand, when In₂O₃ obtained in the laboratory, with low crystallite size, is employed, there is a further change in selectivity toward CH₄, even if the total conversion is lower than that obtained with TiO₂. The selectivity improvement in the heterojunctions is attributed to an enhancement in the charge transfer and separation with the presence of In₂O₃, more pronounced when smaller particles are used as in the case of laboratory-made In₂O₃, as confirmed by time-resolved fluorescence measurements. Ternary systems formed by these heterojunctions with silver nanoparticles reflect a drastic change in selectivity toward methane, confirming the role of silver as an electron collector that favors the charge transfer to the reaction medium.     

Thermo-Exfoliated Graphite Containing CuO/Cu2(OH)3NO3:(Co2+/Fe3+) Composites: Preparation,Characterization and Catalytic Performance in CO Conversion

Thermo-exfoliated graphite (TEG)/CuO/Cu₂(OH)₃NO₃:(Co²⁺/Fe³⁺) composites were prepared using a wet impregnation method and subsequent thermal treatment. The physicochemical characterization of the composites was carried out by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM) and Ar temperature-desorption techniques. The catalytic efficiency toward CO conversion to CO₂ was examined under atmospheric pressure. Characterization of species adsorbed over the composites taken after the activity tests were performed by means of temperature programmed desorption mass-spectrometry (TPD MS). (TEG)/CuO/Cu₂(OH)₃NO₃:(Co²⁺/Fe³⁺) composites show superior performance results if lower temperatures and extra treatment with H₂SO₄ or HNO₃ are used at the preparation stages. The catalytic properties enhancements can be related to the Cu₂(OH)₃NO₃ phase providing reaction centers for the CO conversion. It has been found that prevalence of low-temperature states of desorbed CO₂ over high-temperature ones in the TPD MS spectra is characteristic of the most active composite catalysts.     

Sponge-like CoNi Catalysts Synthesized by Combustion of Reactive Solutions: Stability and Performance for CO2 Hydrogenation

Active and stable catalysts are essential for effective hydrogenation of gaseous CO₂ into valuable chemicals. This work focuses on the structural and catalytic features of single metals, i.e., Co and Ni, as well as bimetallic CoNi alloy catalysts synthesized via combustion of reactive sol-gels. Different characterization methods were used for studying the relationships between the structure, composition, and catalytic activity of the fabricated materials. All catalysts exhibited highly porous sponge-like microstructure. The outermost surfaces of the CoNi alloys were more saturated with Co, while a stoichiometric Co/Ni ratio was observed for the particle’s bulk. Catalytic properties of the as-synthesized powders were studied in the CO₂ hydrogenation reaction at 300 °C for over 80 h of time on stream. All the catalysts demonstrated exceptional selectivity with respect to CH₄ formation. However, the combination of elemental Co and Ni in a single phase resulted in a synergistic effect in bulk alloy catalysts, with activity twofold to threefold that of single-metal catalysts. The activity and stability of the CoNi₃ catalyst were higher than those previously reported for Ni-based catalysts. The reasons for this behavior are discussed.     

CO2 Methanation: Nickel–Alumina Catalyst Prepared by Solid-State Combustion

The development of solvent-free methods for the synthesis of catalysts is one of the main tasks of green chemistry. A nickel–alumina catalyst for CO₂ methanation was synthesized by solid-state combustion method using hexakis-(imidazole) nickel (II) nitrate complex. Using X-ray Powder Diffraction (XRD), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Hydrogen temperature-programmed reduction (H₂-TPR), it was shown that the synthesized catalyst is characterized by the localization of easily reduced nickel oxide on alumina surface. This provided low-temperature activation of the catalyst in the reaction mixture containing 4 vol% CO₂. In addition, the synthesized catalyst had higher activity in low-temperature CO₂ methanation compared to industrial NIAP-07-01 catalyst, which contained almost three times more hard-to-reduce nickel–aluminum spinel. Thus, the proposed approaches to the synthesis and activation of the catalyst make it possible to simplify the catalyst preparation procedure and to abandon the use of solvents, which must be disposed of later on.     

CO2 Adsorption over 3d Transition-Metal Nanoclusters Supported on Pyridinic N3-Doped Graphene: A DFT Investigation

CO₂ adsorption on bare 3d transition-metal nanoclusters and 3d transition-metal nanoclusters supported on pyridinic N₃-doped graphene (PNG) was investigated by employing the density functional theory. First, the interaction of Co₁₃ and Cu₁₃ with PNG was analyzed by spin densities, interaction energies, charge transfers, and HUMO-LUMO gaps. According to the interaction energies, the Co₁₃ nanocluster was adsorbed more efficiently than Cu₁₃ on the PNG. The charge transfer indicated that the Co₁₃ nanocluster donated more charges to the PNG nanoflake than the Cu₁₃ nanocluster. The HUMO-LUMO gap calculations showed that the PNG improved the chemical reactivity of both Co₁₃ and Cu₁₃ nanoclusters. When the CO₂ was adsorbed on the bare 3d transition-metal nanoclusters and 3d transition-metal nanoclusters supported on the PNG, it experienced a bond elongation and angle bending in both systems. In addition, the charge transfer from the nanoclusters to the CO₂ molecule was observed. This study proved that Co₁₃/PNG and Cu₁₃/PNG composites are adequate candidates for CO₂ adsorption and activation.     

Improving the Catalytic CO2 Reduction on Cs2AgBiBr6 by Halide Defect Engineering: A DFT Study

Pb-free double halide perovskites have drawn immense attention in the potential photocatalytic application, due to the regulatable bandgap energy and nontoxicity. Herein, we first present a study for CO₂ conversion on Pb-free halide perovskite Cs₂AgBiBr₆ under state-of-the-art first-principles calculation with dispersion correction. Compared with the previous CsPbBr₃, the cell parameter of Cs₂AgBiBr₆ underwent only a small decrease of 3.69%. By investigating the adsorption of CO, CO₂, NO, NO₂, and catalytic reduction of CO₂, we found Cs₂AgBiBr₆ exhibits modest adsorption ability and unsatisfied potential determining step energy of 2.68 eV in catalysis. We adopted defect engineering (Cl doping, I doping and Br-vacancy) to regulate the adsorption and CO₂ reduction behavior. It is found that CO₂ molecule can be chemically and preferably adsorbed on Br-vacancy doped Cs₂AgBiBr₆ with a negative adsorption energy of −1.16 eV. Studying the CO₂ reduction paths on pure and defect modified Cs₂AgBiBr₆, Br-vacancy is proved to play a critical role in decreasing the potential determining step energy to 1.25 eV. Finally, we probe into the electronic properties and demonstrate Br-vacancy will not obviously promote the process of catalysis deactivation, as there is no formation of deep-level electronic states acting as carrier recombination center. Our findings reveal the process of gas adsorption and CO₂ reduction on novel Pb-free Cs₂AgBiBr₆, and propose a potential strategy to improve the efficiency of catalytic CO₂ conversion towards practical implementation.     

Supercritical CO2-Induced Evolution of Alkali-Activated Slag Cements

The phase changes in alkali-activated slag samples when exposed to supercritical carbonation were evaluated. Ground granulated blast furnace slag was activated with five different activators. The NaOH, Na₂SiO₃, CaO, Na₂SO₄, and MgO were used as activators. C-S-H is identified as the main reaction product in all samples along with other minor reaction products. The X-ray diffractograms showed the complete decalcification of C-S-H and the formation of CaCO₃ polymorphs such as calcite, aragonite, and vaterite. The thermal decomposition of carbonated samples indicates a broader range of CO₂ decomposition. Formation of highly cross-linked aluminosilicate gel and a reduction in unreacted slag content upon carbonation is observed through ²⁹Si and ²⁷Al NMR spectroscopy. The observations indicate complete decalcification of C-S-H with formation of highly cross-linked aluminosilicates upon sCO₂ carbonation. A 20–30% CO₂ consumption per reacted slag under supercritical conditions is observed.     

Dense CO2 as a Solute,Co-Solute or Co-Solvent in Particle Formation Processes: A Review

The application of dense gases in particle formation processes has attracted great attention due to documented advantages over conventional technologies. In particular, the use of dense CO₂ in the process has been subject of many works and explored in a variety of different techniques. This article presents a review of the current available techniques in use in particle formation processes, focusing exclusively on those employing dense CO₂ as a solute, co-solute or co-solvent during the process, such as PGSS (Particles from gas-saturated solutions^®), CPF (Concentrated Powder Form^®), CPCSP (Continuous Powder Coating Spraying Process), CAN-BD (Carbon dioxide Assisted Nebulization with a Bubble Dryer^®), SEA (Supercritical Enhanced Atomization), SAA (Supercritical Fluid-Assisted Atomization), PGSS-Drying and DELOS (Depressurization of an Expanded Liquid Organic Solution). Special emphasis is given to modifications introduced in the different techniques, as well as the limitations that have been overcome.     

CO2 Adsorption on PtCu Sub-Nanoclusters Deposited on Pyridinic N-Doped Graphene: A DFT Investigation

To reduce the CO₂ concentration in the atmosphere, its conversion to different value-added chemicals plays a very important role. Nevertheless, the stable nature of this molecule limits its conversion. Therefore, the design of highly efficient and selective catalysts for the conversion of CO₂ to value-added chemicals is required. Hence, in this work, the CO₂ adsorption on Pt_4-xCu_x (x = 0–4) sub-nanoclusters deposited on pyridinic N-doped graphene (PNG) was studied using the density functional theory. First, the stability of Pt_4-xCu_x (x = 0–4) sub-nanoclusters supported on PNG was analyzed. Subsequently, the CO₂ adsorption on Pt_4-xCu_x (x = 0–4) sub-nanoclusters deposited on PNG was computed. According to the binding energies of the Pt_4-xCu_x (x = 0–4) sub-nanoclusters on PNG, it was observed that PNG is a good material to stabilize the Pt_4-xCu_x (x = 0–4) sub-nanoclusters. In addition, charge transfer occurred from Pt_4-xCu_x (x = 0–4) sub-nanoclusters to the PNG. When the CO₂ molecule was adsorbed on the Pt_4-xCu_x (x = 0–4) sub-nanoclusters supported on the PNG, the CO₂ underwent a bond length elongation and variations in what bending angle is concerned. In addition, the charge transfer from Pt_4-xCu_x (x = 0–4) sub-nanoclusters supported on PNG to the CO₂ molecule was observed, which suggests the activation of the CO₂ molecule. These results proved that Pt_4-xCu_x (x = 0–4) sub-nanoclusters supported on PNG are adequate candidates for CO₂ adsorption and activation.     

Detecting long-term metabolic shifts using isotopomers: CO2-driven suppression of photorespiration in C3 plants over the 20th century

Terrestrial vegetation currently absorbs approximately a third of anthropogenic CO₂ emissions, mitigating the rise of atmospheric CO₂. However, terrestrial net primary production is highly sensitive to atmospheric CO₂ levels and associated climatic changes. In C₃ plants, which dominate terrestrial vegetation, net photosynthesis depends on the ratio between photorespiration and gross photosynthesis. This metabolic flux ratio depends strongly on CO₂ levels, but changes in this ratio over the past CO₂ rise have not been analyzed experimentally. Combining CO₂ manipulation experiments and deuterium NMR, we first establish that the intramolecular deuterium distribution (deuterium isotopomers) of photosynthetic C₃ glucose contains a signal of the photorespiration/photosynthesis ratio. By tracing this isotopomer signal in herbarium samples of natural C₃ vascular plant species, crops, and a Sphagnum moss species, we detect a consistent reduction in the photorespiration/photosynthesis ratio in response to the ∼100-ppm CO₂ increase between ∼1900 and 2013. No difference was detected in the isotopomer trends between beet sugar samples covering the 20th century and CO₂ manipulation experiments, suggesting that photosynthetic metabolism in sugar beet has not acclimated to increasing CO₂ over >100 y. This provides observational evidence that the reduction of the photorespiration/photosynthesis ratio was ca. 25%. The Sphagnum results are consistent with the observed positive correlations between peat accumulation rates and photosynthetic rates over the Northern Hemisphere. Our results establish that isotopomers of plant archives contain metabolic information covering centuries. Our data provide direct quantitative information on the “CO₂ fertilization” effect over decades, thus addressing a major uncertainty in Earth system models.Atmospheric CO₂ levels have increased from ∼200 ppm during the last ice age to currently 400 ppm, and they may, according to pessimistic scenarios, exceed 1,000 ppm in the year 2100 (1). Understanding plant responses to increasing CO₂ is currently hampered by two fundamental limitations: First, it is unknown how well manipulation experiments represent responses to the gradual CO₂ increase over decades and centuries. In Free-Air CO₂ Enrichment (FACE) experiments, which most closely mimic natural conditions, increases in [CO₂] generally increase plant growth, but this “CO₂ fertilization” effect often declines after a few years of enrichment (2). Such transient responses may be related to the step increases in [CO₂] used in the experiments, their limited duration (2), or factors other than CO₂ becoming limiting (3). Second, in response to the [CO₂] increase since industrialization, genetic (4) and phenotypic plant responses (5–7) have been observed. Although century-scale changes have been detected in carbon isotopes (δ¹³C) and attributed to [CO₂], these responses are tied to differences in intercellular substrate concentrations that reflect several metabolic fluxes and diffusion processes (8). However, the responses do not measure the metabolic fluxes directly. The consequently poor constraint of the magnitude of the CO₂ fertilization effect over decadal to century time scales (1, 9) is a major source of uncertainty in parameterizations of Earth system models (1, 10) and crop productivity models (11, 12). Therefore, observational data are essential to enable global carbon models to provide reliable long-term predictions.Plants that fix carbon by the C₃ photosynthetic pathway (C₃ plants) account for most (ca. 75%) global primary production and human food production (13). In C₃ plants, CO₂ initially reacts with D-ribulose-1,5-bisphosphate (RubP) catalyzed by the enzyme D-ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), but this enzyme also has a competing O₂ fixation activity (14). The resulting carboxylation and oxygenation processes create photosynthetic and photorespiratory metabolic fluxes (15), which, respectively, cause C gains and losses for plants (Fig. 1), and which, globally, are among the largest biogeochemical C fluxes (16). Thus, the balance between these metabolic fluxes is a major determinant of the net primary productivity of C₃ plants in response to increasing [CO₂], and therefore is a major influence on the CO₂ sink strength of terrestrial vegetation, including the performance of C₃ crop plants.Open in a separate windowFig. 1.Overview of metabolic pathways emanating from RubP by Rubisco activity. Upon carboxylation, 3-phosphoglycerate (3-PGA) molecules are formed from C1−C2 and C3−C5 of RuBP. Upon oxygenation, one 3-PGA molecule is formed from C3−C5 of RubP, and up to one-half 3-PGA is formed via the photorespiration pathway through the peroxisome and mitochondrion. The color coding of hydrogen atoms tracks the biochemical origins of hydrogens at C3 of 3-PGA, which give rise to the isotopomer signal encoded in the colored C6H₂ group of glucose.Stable isotopes such as deuterium (D) are key tools for probing plants’ ecological and biogeochemical interactions with their environment. Conventional compound-specific stable isotope methods provide the D/H ratio, usually expressed as δD (17), of an entire molecule, that is, averaged over all intramolecular positions in the molecule. This means that conventional stable isotope methods are based on isotopologues, which, by definition, differ in the number of isotopic substitutions. The same situation applies to the carbon isotope ratio ¹³C/¹²C expressed as δ¹³C. The δD or δ¹³C signals of plant metabolites largely depend on three mechanisms: the isotope signatures of the plant’s H₂O and CO₂ sources, isotope fractionation during substrate uptake, and isotope fractionation during biosynthesis, primarily enzyme isotope effects.It is well established that enzyme isotope effects influence stable isotope abundance in specific intramolecular positions (18, 19). A molecule carrying an isotope substitution in a specific intramolecular position is termed an isotopomer. Deuterium isotopomer abundances can be measured by NMR. Glucose, measured as a derivative that gives highly resolved deuterium NMR spectra (see Methods), gives rise to seven signals with variable integrals (Fig. 2A), which reflect the abundance of each of the seven D isotopomers of glucose. Isotopomer variation encodes metabolic information (18, 19), but isotopomers have not yet been used for unraveling long-term metabolic changes induced by environmental drivers.Open in a separate windowFig. 2.Effect of [CO₂] on the D6^S/D6^R isotopomer ratio of photosynthetically generated glucose moieties in sunflower (H. annuus). (A) Deuterium NMR spectrum of a glucose derivative displaying one signal for each of the seven isotopomers of glucose. The signals’ integrals are proportional to the isotopomer abundances. (B) Excerpts of deuterium NMR spectra of glucose prepared from sunflower leaf starch, showing signals arising from the D6^S and D6^R isotopomers of the C6H₂ group of glucose. The solid and dashed spectra were acquired from glucose formed at 280 ppm and 1,500 ppm CO₂, respectively. The dashed spectrum has been shifted sideways to ease comparison. (C) Dependence of the D6^S/D6^R ratio of glucose from sunflower leaf starch on 1/[CO₂] (in units of 10⁻³ ppm⁻¹) during growth [r² = 0.88, slope 0.057 ±0.006 (SEM), P < 10⁻⁷, n = 17, individual plants except for 180 and 280 ppm, where material from two to four plants had to be pooled for each sample].Here, we establish isotopomers as a ground-breaking technique for evaluating long-term effects of gradual [CO₂] increase on plant metabolism at the biochemical level. We first use CO₂ manipulation experiments to identify an isotopomer signal that reflects the Rubisco oxygenation/carboxylation ratio of C₃ plants. We then trace the signal in herbarium samples of wild plants, crops, and Sphagnum mosses, to estimate changes in metabolic flux ratios in photosynthetic carbon metabolism of C₃ plants over the past century.     

Morphology Design and Fabrication of Bio-Inspired Nano-MgO–Mg(OH)2 via Vapor Steaming to Enable Bulk CO2 Diffusion and Capture

The absorption of CO₂ on MgO is being studied in depth in order to enhance carbon engineering. Production of carbonate on MgO surfaces, such as MgCO₃, for example, has been shown to hinder further carbon lattice transit and lower CO₂ collecting efficiency. To avoid the carbonate blocking effect, we mimic the water harvesting nano-surface systems of desert beetles, which use alternate hydrophobic and hydrophilic surface domains to collect liquid water and convey condensed droplets down to their mouths, respectively. We made CO₂-philic MgO and CO₂-phobic Mg(OH)₂ nanocomposites from electrospun nano-MgO by vapor steaming for 2–20 min at 100 °C. The crystal structure, morphology, and surface properties of the produced samples were instrumentally characterized using XRD, SEM, XPS, BET, and TGA. We observed that (1) fiber morphology shifted from hierarchical particle and sheet-like structures to flower-like structures, and (2) CO₂ capture capacity shifted by around 25%. As a result, the carbonate production and breakdown processes may be managed and improved using vapor steaming technology. These findings point to a new CO₂ absorption technique and technology that might pave the way for more CO₂ capture, mineralization, and fuel synthesis options.     

CeFeO3–CeO2–Fe2O3 Systems: Synthesis by Solution Combustion Method and Catalytic Performance in CO2 Hydrogenation

Rare-earth orthoferrites have found wide application in thermocatalytic reduction-oxidation processes. Much less attention has been paid, however, to the production of CeFeO₃, as well as to the study of its physicochemical and catalytic properties, in particular, in the promising process of CO₂ utilization by hydrogenation to CO and hydrocarbons. This study presents the results of a study on the synthesis of CeFeO₃ by solution combustion synthesis (SCS) using various fuels, fuel-to-oxidizer ratios, and additives. The SCS products were characterized by XRD, FTIR, N₂-physisorption, SEM, DTA–TGA, and H₂-TPR. It has been established that glycine provides the best yield of CeFeO₃, while the addition of NH₄NO₃ promotes an increase in the amount of CeFeO₃ by 7–12 wt%. In addition, the synthesis of CeFeO₃ with the participation of NH₄NO₃ makes it possible to surpass the activity of the CeO₂–Fe₂O₃ system at low temperatures (300–400 °C), as well as to increase selectivity to hydrocarbons. The observed effects are due to the increased gas evolution and ejection of reactive FeO_x nanoparticles on the surface of crystallites, and an increase in the surface defects. CeFeO₃ obtained in this study allows for achieving higher CO₂ conversion compared to LaFeO₃ at 600 °C.     

Effect of Bimetallic Dimer-Embedded TiO2(101) Surface on CO2 Reduction: The First-Principles Calculation

The first-principles calculation was used to explore the effect of a bimetallic dimer-embedded anatase TiO₂(101) surface on CO₂ reduction behaviors. For the dimer-embedded anatase TiO₂(101) surface, Zn-Cu, Zn-Pt, and Zn-Pd dimer interstitials could stably stay on the TiO₂(101) surface with a binding energy of about −2.36 eV, as well as the electronic states’ results. Meanwhile, the results of adsorption energy, structure parameters, and electronic states indicated that CO₂ was first physically and then chemically adsorbed much more stably on these three kinds of dimer-embedded TiO₂(101) substrate with a small barrier energy of 0.03 eV, 0.23 eV, and 0.12 eV. Regarding the reduction process, the highest-energy barriers of the CO₂ molecule on the Zn-Cu dimer-embedded TiO₂(101) substrate was 0.31 eV, which largely benefited the CO₂-reduction reaction (CO₂RR) activity and was much lower than that of the other two kinds of Zn-Pt and Cu-Pt dimer-TiO₂ systems. Simultaneously, the products CO* and *O* of CO₂ reduction were firmly adsorbed on the dimer-embedded TiO₂(101) surface. Our results indicated that a non-noble Zn-Cu dimer might be a more suitable and economical choice, which might theoretically promote the designation of high CO₂RR performance on TiO₂ catalysts.     

Use of a Gemini-Surfactant Synthesized from the Mango Seed Oil as a CO2-Corrosion Inhibitor for X-120 Steel

A gemini surfactant imidazoline type, namely N-(3-(2-fatty-4,5-dihydro-1H-imidazol-1-yl) propyl) fatty amide, has been obtained from the fatty acids contained in the mango seed and used as a CO₂ corrosion inhibitor for API X-120 pipeline steel. Employed techniques involved potentiodynamic polarization curves, linear polarization resistance, and electrochemical impedance spectroscopy. These tests were supported by detailed scanning electronic microscopy (SEM) and Raman spectroscopy studies. It was found that obtained gemini surfactant greatly decreases the steel corrosion rate by retarding both anodic and cathodic electrochemical reactions, with an efficiency that increases with an increase in its concentration. Gemini surfactant inhibits the corrosion of steel by the adsorption mechanism, and it is adsorbed on to the steel surface according to a Langmuir model in a chemical type of adsorption. SEM and Raman results shown the presence of the inhibitor on the steel surface.     

CO2 Adsorption on Activated Carbons Prepared from Molasses: A Comparison of Two and Three Parametric Models

Activated carbons with different textural characteristic were derived by the chemical activation of raw beet molasses with solid KOH, while the activation temperature was changed in the range 650 °C to 800 °C. The adsorption of CO₂ on activated carbons was investigated. Langmuir, Freundlich, Sips, Toth, Unilan, Fritz-Schlunder, Radke-Prausnitz, Temkin-Pyzhev, Dubinin-Radushkevich, and Jovanovich equations were selected to fit the experimental data of CO₂ adsorption. An error analysis (the sum of the squares of errors, the hybrid fractional error function, the average relative error, the Marquardt’s percent standard deviation, and the sum of the absolute errors) was conducted to examine the effect of using various error standards for the isotherm model parameter calculation. The best fit was observed to the Radke-Prausnitz model.     

Adsorption and Oxidation of CO on Ceria Nanoparticles Exposing Single-Atom Pd and Ag: A DFT Modelling

Various CO_x species formed upon the adsorption and oxidation of CO on palladium and silver single atoms supported on a model ceria nanoparticle (NP) have been studied using density functional calculations. For both metals M, the ceria-supported MCO_x moieties are found to be stabilised in the order MCO < MCO₂ < MCO₃, similar to the trend for CO_x species adsorbed on M-free ceria NP. Nevertheless, the characteristics of the palladium and silver intermediates are different. Very weak CO adsorption and the small exothermicity of the CO to CO₂ transformation are found for O₄Pd site of the Pd/Ce₂₁O₄₂ model featuring a square-planar coordination of the Pd²⁺ cation. The removal of one O atom and formation of the O₃Pd site resulted in a notable strengthening of CO adsorption and increased the exothermicity of the CO to CO₂ reaction. For the analogous ceria models with atomic Ag instead of atomic Pd, these two energies became twice as small in magnitude and basically independent of the presence of an O vacancy near the Ag atom. CO₂-species are strongly bound in palladium carboxylate complexes, whereas the CO₂ molecule easily desorbs from oxide-supported AgCO₂ moieties. Opposite to metal-free ceria particle, the formation of neither PdCO₃ nor AgCO₃ carbonate intermediates before CO₂ desorption is predicted. Overall, CO oxidation is concluded to be more favourable at Ag centres atomically dispersed on ceria nanostructures than at the corresponding Pd centres. Calculated vibrational fingerprints of surface CO_x moieties allow us to distinguish between CO adsorption on bare ceria NP (blue frequency shifts) and ceria-supported metal atoms (red frequency shifts). However, discrimination between the CO₂ and CO₃²⁻ species anchored to M-containing and bare ceria particles based solely on vibrational spectroscopy seems problematic. This computational modelling study provides guidance for the knowledge-driven design of more efficient ceria-based single-atom catalysts for the environmentally important CO oxidation reaction.     

A proposed potential role for increasing atmospheric CO2 as a promoter of weight gain and obesity

Human obesity has evolved into a global epidemic. Interestingly, a similar trend has been observed in many animal species, although diet composition, food availability and physical activity have essentially remained unchanged. This suggests a common factor—potentially an environmental factor affecting all species. Coinciding with the increase in obesity, atmospheric CO₂ concentration has increased more than 40%. Furthermore, in modern societies, we spend more time indoors, where CO₂ often reaches even higher concentrations. Increased CO₂ concentration in inhaled air decreases the pH of blood, which in turn spills over to cerebrospinal fluids. Nerve cells in the hypothalamus that regulate appetite and wakefulness have been shown to be extremely sensitive to pH, doubling their activity if pH decreases by 0.1 units. We hypothesize that an increased acidic load from atmospheric CO₂ may potentially lead to increased appetite and energy intake, and decreased energy expenditure, and thereby contribute to the current obesity epidemic.     

A Novel Sustainable Process for Multilayer Graphene Synthesis Using CO2 from Ambient Air

Graphene produced by different methods can present varying physicochemical properties and quality, resulting in a wide range of applications. The implementation of a novel method to synthesize graphene requires characterizations to determine the relevant physicochemical and functional properties for its tailored application. We present a novel method for multilayer graphene synthesis using atmospheric carbon dioxide with characterization. Synthesis begins with carbon dioxide sequestered from air by monoethanolamine dissolution and released into an enclosed vessel. Magnesium is ignited in the presence of the concentrated carbon dioxide, resulting in the formation of graphene flakes. These flakes are separated and enhanced by washing with hydrochloric acid and exfoliation by ammonium sulfate, which is then cycled through a tumble blender and filtrated. Raman spectroscopic characterization, FTIR spectroscopic characterization, XPS spectroscopic characterization, SEM imaging, and TEM imaging indicated that the graphene has fifteen layers with some remnant oxygen-possessing and nitrogen-possessing functional groups. The multilayer graphene flake possessed particle sizes ranging from 2 µm to 80 µm in diameter. BET analysis measured the surface area of the multilayer graphene particles as 330 m²/g, and the pore size distribution indicated about 51% of the pores as having diameters from 0.8 nm to 5 nm. This study demonstrates a novel and scalable method to synthesize multilayer graphene using CO₂ from ambient air at 1 g/kWh electricity, potentially allowing for multilayer graphene production by the ton. The approach creates opportunities to synthesize multilayer graphene particles with defined properties through a careful control of the synthesis parameters for tailored applications.