Carbon Dioxide Activation Research Articles

Production and characterization of activated carbon from barley straw by physical activation with carbon dioxide and steam

In recent years, the growth of environmental protection policies has generated an increase in the global demand for activated carbon, the most widely used adsorbent in many industrial sectors, and with good prospects of implementation in others such as energy storage (electrodes in supercapacitors) and agriculture (fertilizer production). This demand is driving by the search for renewable, abundant and low-cost precursor materials, as an alternative to traditional fossil sources. This study investigates the production of activated carbon from barley straw using physical activation method with two different activating agents, carbon dioxide and steam. Experimental tests under different conditions at each stage of the process, carbonization and activation, have been conducted in order to maximize the BET surface area and microporosity of the final product. During the carbonization stage, temperature and heating rate have been found to be the most relevant factors, while activation temperature and hold time played this role during activation. Optimal conditions for the activation stage were obtained at 800 °C and a hold time of 1 h in the case of activation with carbon dioxide and at 700 °C and a hold time of 1 h in the case of activation with steam. The maximum BET surface area and micropore volume achieved by carbon dioxide activation were of 789 m2/g and 0.3268 cm3/g while for steam activation were 552 m2/g and 0.2304 cm3/g, which represent respectively an increase of more than 43% and 42% for the case of activation with carbon dioxide.

An Iron Complex with a Bent, O‐Coordinated CO2 Ligand Discovered by Femtosecond Mid‐Infrared Spectroscopy

AbstractThe activation of carbon dioxide by transition metals is widely recognized as a key step for utilizing this greenhouse gas as a renewable feedstock for the sustainable production of fine chemicals. However, the dynamics of CO2 binding and unbinding to and from the ligand sphere of a metal have never been observed in the time domain. The ferrioxalate anion is used in aqueous solution as a unique model system for these dynamics and femtosecond UV‐pump mid‐infrared‐probe spectroscopy is applied to explore its photoinduced primary processes in a time‐resolved fashion. Following optical excitation, a neutral CO2 molecule is expelled from the complex within about 500 fs to generate a highly intriguing pentacoordinate ferrous dioxalate that carries a bent carbon dioxide radical anion ligand, that is, a reductively activated form of CO2, which is end‐on‐coordinated to the metal center by one of its two oxygen atoms.

An Iron Complex with a Bent, O-Coordinated CO2 Ligand Discovered by Femtosecond Mid-Infrared Spectroscopy.

The activation of carbon dioxide by transition metals is widely recognized as a key step for utilizing this greenhouse gas as a renewable feedstock for the sustainable production of fine chemicals. However, the dynamics of CO2 binding and unbinding to and from the ligand sphere of a metal have never been observed in the time domain. The ferrioxalate anion is used in aqueous solution as a unique model system for these dynamics and femtosecond UV-pump mid-infrared-probe spectroscopy is applied to explore its photoinduced primary processes in a time-resolved fashion. Following optical excitation, a neutral CO2 molecule is expelled from the complex within about 500 fs to generate a highly intriguing pentacoordinate ferrous dioxalate that carries a bent carbon dioxide radical anion ligand, that is, a reductively activated form of CO2 , which is end-on-coordinated to the metal center by one of its two oxygen atoms.

Design of Copper-Based Bimetallic Nanoparticles for Carbon Dioxide Adsorption and Activation.

Cu-based nanoparticles (NPs) are promising candidates for the catalytic hydrogenation of CO2 to useful chemicals because of their low cost. However, CO2 adsorption and activation on Cu is not feasible. In this work we demonstrate a computational framework that identifies Cu-based bimetallic NPs able to adsorb and activate CO2 based on DFT calculations. We screen a series of heteroatoms on Cu-based NPs based on their preference to occupy a surface site on the NP and to adsorb and activate CO2 . We revealed two descriptors for CO2 adsorption on the bimetallic NPs, the heteroatom (i) local d-band center and (ii) electropositivity, which both drive an effective charge transfer from the NP to CO2 . We identified the CuZr bimetallic NP as a candidate nanostructure for CO2 adsorption and showed that although the Zr sites can be oxidized because of their high oxophilicity, they are still able to adsorb and activate CO2 strongly. Importantly, our computational results are verified by targeted synthesis, characterization, and CO2 adsorption experiments that demonstrate that i) Zr segregates on the surface of Cu, ii) Zr is oxidized to form a bimetallic mixed CuZr oxide catalyst, which iii) can strongly adsorb CO2 , whereas Cu NPs cannot. Overall our work highlights the importance of the generation of binding sites on a NP surface based on (catalyst) stability and electronic structure properties, which can lead to the design of more effective CO2 reduction catalysts.

Characterization of Intermediate Oxidation States in CO2 Activation.

Redox chemistry during the activation of carbon dioxide involves changing the charge state in a CO2 molecular unit. However, such changes are usually not well described by integer formal charges, and one can think of COO functional units as being in intermediate oxidation states. In this article, we discuss the properties of CO2 and CO2-based functional units in various charge states. Besides covering isolated CO2 and its ions, we describe the CO2-based ionic species formate, oxalate, and carbonate. Finally, we provide an overview of CO2-based functional groups and ligands in clusters and metal-organic complexes.

Proton sponge as a new efficient catalyst for carbon dioxide transformation to methanol: Theoretical approach

In this research, thermodynamic and kinetic aspects of methanol production by carbon dioxide in the presence of the proton sponge as the reaction catalyst and borane molecule as the reductive reagent were investigated theoretically. Proton sponge as the super base plays a key role in the carbon dioxide activation reaction. A comprehensive study was performed on the reaction mechanism and the most probable routes of the reaction. The function of six proton sponges on the catalytic cycle of methanol production was evaluated in the gas phase and in solvent. It was shown that the catalyst performance is proportional to the dihedral angles (θ) between their aromatic rings. Finally, one of the proton sponges was anticipated as the best catalyst for the reaction. In the mechanism evaluation, three routes were considered for the reaction, one route has been proposed as the most possible route of the reaction through the thermodynamic and kinetic analyses.

Mesoporous activated carbon prepared from macadamia nut shell waste by carbon dioxide activation: Comparative characterisation and study of methylene blue removal from aqueous solution

AbstractActivated carbons are the most widely used adsorbents; however, producing high‐performance mesoporous activated carbons with simple technology still remains a challenge. In this research, waste macadamia nut shell (MNS) was explored as precursor for preparing mesoporous activated carbons by carbon dioxide activation. The material characteristics of MNS‐based activated carbon (MAC) were thoroughly examined in comparison with a premium‐grade commercial activated carbon (CAC). MAC and CAC had specific surface areas of 830 and 1,299 m2 g−1, respectively. Although CAC had a predominantly microporous structure, about 74% of the pore volume of MAC is composed of mesopores. Adsorption performances were evaluated in batch experiments using methylene blue model pollutant and demonstrated 135 and 181 mg g−1 saturation capacities for MAC and CAC, respectively. Non‐linear regression found that the fractal‐like pseudo first‐order model accurately described sorption kinetics, and intraparticle diffusion was the rate‐limiting step. Among 6 established isotherm models, the Liu equilibrium model showed the best statistics. Thermodynamic analysis verified that the process was favourable and involved physisorption. These results show that valuable mesoporous activated carbons can be prepared from the biowaste MNS with simple production technology to suit environmental and industrial applications.

Preparation of hierarchically porous sulfur- and oxygen-co-doped carbon for gas uptake and lithium-ion battery

Heteroatom-doped porous carbons have attracted great concern owing to their enhanced physicochemical property. In this study, a hierarchically porous sulfur- and oxygen-co-doped carbon (PSOC) is obtained through direct carbon dioxide activation of poly(3,4-ethylenedioxythiophene) with abundant sulfur and oxygen atoms in the polymer backbone. Both sulfur and oxygen heteroatoms are introduced into carbon matrix through a rational preparation approach. The morphology, microstructure, and chemical property of the as-prepared PSOC have been analyzed by using various characterization methods, including scanning/transmission electron microscopy, nitrogen sorption test, Raman spectroscopy, and X-ray photoelectron spectroscopy. PSOC displays a high specific surface area (1160 m2 g−1) and hierarchically porous structure (micropores, mesopores, and macropores). Owing to its excellent surface property and porosity parameters, PSOC exhibits a good gas adsorption capacity (carbon dioxide: 16.6 wt %; methane: 2.7 wt %) at 273 K under 1.0 bar when used as a gas sorbent. In addition, PSOC as an anode material shows a high reversible capacity of 931 mA h g−1 at 100 mA g−1 and excellent cycling performance (504 mA h g−1 at 200 mA g−1 after 200 cycles). As a result, the as-prepared PSOC demonstrates a promising potential in the fields of gas adsorption and energy storage.

The activation of carbon dioxide by first row transition metals (Sc-Zn).

The activation of CO2 by chloride-tagged first-row transition metal anions [ClM]- (M = Sc-Zn), was examined by mass spectrometry, quantum chemical calculations, and statistical analysis. The direct formation of [ClM(CO2)]- complexes was demonstrated in the reaction between [ClM]- and neutral CO2. In addition, the reverse reaction was investigated by energy-variable collisionally induced dissociation (CID) of the corresponding [ClM(CO2)]- anions generated in-source. Five different mono- and bi-dentate binding motifs present in the ion/CO2 complexes were identified by quantum chemical calculations and the relative stability of each of these isomers was established and analyzed for all first-row transition metals based on the experimental and theoretical ion/molecule binding energies. It was found that the early first row transition metals form strong covalent bonds with the neutral CO2 molecule, while the late ones and in particular copper and zinc are weakly bonded. Using simple valence bond Lewis diagrams, the different binding motifs and their relative stabilities across the first row were described using multi-configurational self consistent field (MSCSCF) wavefunctions in a quantitative manner based on the electronic structure of the individual metals. This analysis provides an explanation for the change of the most favorite bonding motif of the transition metals with CO2 along the 1st transition metal row. The nature of the activated CO2 complex and the relationship between its stability and other structural and spectral properties was also analyzed by Principal Component Analysis (PCA) and artificial neural networks.

Absorption and Activation of Carbon Dioxide by Functionalized Ionic Liquid for the Preparation of Formic Acid

Absorption and Activation of Carbon Dioxide by Functionalized Ionic Liquid for the Preparation of Formic Acid

Current advances in the catalytic conversion of carbon dioxide by molecular catalysts: an update.

Due to the high emissions of CO2 and the related environmental impact, the chemical transformation of CO2 to useful industrially relevant products or their precursor is of significant interest. Recycling CO2 as a building block for the synthesis of chemicals may not only reduce further emission by at least replacing oil-derived feedstocks, but also provide the advantages of CO2 as an inexpensive, non-toxic and easily available substrate. The catalytic conversion of CO2 into small, useful molecules such as carbonates, methyl amines, methanol, formic acid, etc. by molecular catalysts is an interesting topic that has strongly developed in recent years. This review provides an overview of current scientific progress in the activation and conversion of carbon dioxide with industrially and scientifically relevant substrates using molecular catalysts. Metal-based catalysts are presented in the first part of the review whereas metal-free systems are described in the second part.

Selective and catalytic carbon dioxide and heteroallene activation mediated by cerium N-heterocyclic carbene complexes.

A series of rare earth complexes of the form Ln(LR)3 supported by bidentate ortho-aryloxide-NHC ligands are reported (LR = 2-O-3,5-tBu2-C6H2(1-C{N(CH)2N(R)})); R = iPr, tBu, Mes; Ln = Ce, Sm, Eu). The cerium complexes cleanly and quantitatively insert carbon dioxide exclusively into all three cerium carbene bonds, forming Ce(LR·CO2)3. The insertion is reversible only for the mesityl-substituted complex Ce(LMes)3. Analysis of the capacity of Ce(LR)3 to insert a range of heteroallenes that are isoelectronic with CO2 reveals the solvent and ligand size dependence of the selectivity. This is important because only the complexes capable of reversible CO2-insertion are competent catalysts for catalytic conversions of CO2. Preliminary studies show that only Ce(LMes·CO2)3 catalyses the formation of propylene carbonate from propylene oxide under 1 atm of CO2 pressure. The mono-ligand complexes can be isolated from reactions using LiCe(NiPr2)4 as a starting material; LiBr adducts [Ce(LR)(NiPr2)Br·LiBr(THF)]2 (R = Me, iPr) are reported, along with a hexanuclear N-heterocyclic dicarbene [Li2Ce3(OArCMe-H)3(NiPr2)5(THF)2]2 by-product. The analogous para-aryloxide-NHC proligand (p-LMes = 4-O-2,6-tBu2-C6H2(1-C{N(CH)2NMes}))) has been made for comparison, but the rare earth tris-ligand complexes Ln(p-LMes)3(THF)2 (Ln = Y, Ce) are too reactive for straightforward Lewis pair separated chemistry to be usefully carried out.

Effect of Water-binder Ratio and Blaine fineness on the Carbon Dioxide Activation of a Cement-Free Binder

Effect of Water-binder Ratio and Blaine fineness on the Carbon Dioxide Activation of a Cement-Free Binder

Understanding the thermodynamic and kinetic performances of the substituted phosphorus ylides as a new class of compounds in carbon dioxide activation

The investigation of thermodynamic and kinetic behavior of the carbon dioxide activation in the presence of the phosphorus ylides (P-ylides) is the main purpose of this study. Different substituents on the carbon atom of the P-ylides have different effects on the P-ylides performances in the carbon dioxide activation. The accessibility of the lone pair electrons on the carbon atom has a remarkable effect on the thermodynamic features of the reaction. A greater involvement of this carbon atom with the orbitals of the substituted groups decreases its reactivity in the CO2 fixation and Gibbs energy increment. A similarity in the energy levels of the involved orbitals of the carbon dioxide and P-ylides is another factor that affects the thermodynamics of the reaction. The proximity of the energy levels corresponding to the lone pair electrons on the carbon atom of the P-ylides and π*CO of the carbon dioxide has a good relationship with the ΔG values and progress of the reaction. However, the results of the activation strain model reveal that the activation energy of the reaction is influenced by the strain activation energy of CO2 and a greater distortion from the equilibrium geometry of CO2 increases the global energy barrier.

Light-Enhanced Carbon Dioxide Activation and Conversion by Effective Plasmonic Coupling Effect of Pt and Au Nanoparticles.

Photocatalytic reduction of carbon dioxide (CO2) is attractive for the production of valuable fuels and mitigating the influence of greenhouse gas emission. However, the extreme inertness of CO2 and the sluggish kinetics of photoexcited charge carrier transfer process greatly limit the conversion efficiency of CO2 photoreduction. Herein, we report that the plasmonic coupling effect of Pt and Au nanoparticles (NPs) profoundly enhances the efficiency of CO2 reduction through dry reforming of methane reaction assisted by light illumination, reducing activation energies for CO2 reduction ∼30% below thermal activation energies and achieving a reaction rate 2.4 times higher than that of the thermocatalytic reaction. UV-visible (vis) absorption spectra and wavelength-dependent performances show that not only UV but also visible light play important roles in promoting CO2 reduction due to effective localized surface plasmon resonance (LSPR) coupling between Pt and Au NPs. Finite-difference time-domain simulations and in situ diffuse reflectance infrared Fourier transform spectroscopy further reveal that effective coupling LSPR effect generates strong local electric fields and excites high concentration of hot electrons to activate the reactants and intermediate species, reduce the activation energies, and increase the reaction rate. This work provides a new pathway toward the efficient plasmon-enhanced chemical reactions via reducing the activation energies by utilizing solar energy.

Modeling and optimization of carbon dioxide methanation via in situ hydrogen generated from aluminum foil and alkaline water by Box–Behnken design

The catalytic activity of carbon dioxide (CO2) methanation by in situ hydrogen generated from aluminum foil (Al) and alkaline water over a novel catalyst (AHZ–CM) was investigated. Response surface method- ology involving Box–Behnken design (RSM-BBD) was implemented for optimization where the reaction temperature was found to be the utmost significant effective factor, followed by H2/CO2 ratio and weight catalyst loading. The optimum condition for CO2 conversion was at 3.29g of weight catalyst loading, H2/CO2 ratio of 4.08 and reaction temperature of 276.7 °C which resulted in 97.5% of CO2 conversion. The result was approximately in agreement with the predicted result found by RSM which achieved 99.9% CO2 conversion. Interestingly, this study proved that the hydrogen gas production from Al and alkaline water can be used in situ reaction and the novel catalyst (AHZ–CM) would be an excellent candidate to be used for CO2 methanation reaction.

Pacman Compounds: From Energy Transfer to Cooperative Catalysis.

In this Concept article we present the syntheses and application of homo and heterodinuclear "Pacman" compounds. This architecture implies that two metal coordination fragments are brought in close vicinity to each other via a covalent linkage to either support energy transfer between the two units or cooperative transformation of a substrate. Nature has shown that the combination of metal fragments, in particular two different metals, can dramatically improve the efficiency of small molecule activation. We exemplify this strategy for the activation of water, dioxygen and carbon dioxide. Furthermore, we present artificial systems in which a positive effect on the catalytic performance because of the combination of two (different) metal centers could be observed. Thus, Pacman-type compounds are very well suited as structural and functional models for their biological counterparts.

Nitrogen-doped and nanostructured carbons with high surface area for enhanced oxygen reduction reaction

The development of highly-efficient, inexpensive, and stable electrocatalysts as alternatives to platinum-based materials for the oxygen reduction reaction (ORR) is crucial to various energy storage and conversion systems, such as metal–air batteries and fuel cells. Herein, we have successfully prepared three kinds of hierarchically porous nitrogen-doped carbons with different morphologies (particles, nanowires, and nanoribbons) through a carbon dioxide activation process. The porous properties and catalytic performance of the nitrogen-doped porous carbons are dramatically and clearly improved through changing the morphology of polypyrrole precursors. Among these nitrogen-doped porous carbons, the nitrogen-doped and nanostructured carbon with the morphology of nanoribbons possesses the highest specific surface area (1130 m2 g−1) and displays the best ORR activity with the largest electron transfer number (3.67) and the most positive onset potential (0.86 V vs. RHE) in oxygen-saturated aqueous KOH solution (0.1 M). This enhanced ORR performance can be attributed to nitrogen-doping, a hierarchically porous structure, and large specific surface area.

Phosphorus ylides as a new class of compounds in CO2 activation: Thermodynamic and kinetic studies

Phosphorus ylides (P-ylides) including aliphatic or aromatic chains bonded to phosphorous atom and P-ylides containing NR2 groups are two kinds of P-ylides that are considered in carbon dioxide activation processes. Based on theoretical results an acceptable correlation between the Gibbs energy of the reaction and the minimum of the molecular electrostatic potential (MESP) (Vmin) was obtained. The product of the reaction is P-ylide-CO2 adducts. Because of a more negative character of the Vmin values, these adducts are potentially better organocatalysts than the P-ylides for CO2 transformation. Also, natural bond orbital (NBO) analyses show that hyperconjugation and negative hyperconjugation effects are responsible for the magnitude of the electron density of the bond between nucleophilic carbon and phosphorous atom. These effects have a remarkable influence on the kinetic behavior of P-ylides along the CO2 activation. Finally, it can be concluded that P-ylides containing aliphatic chains such as P(Me)3CH2, P(Et)3CH2 are kinetically and thermodynamically more efficient in CO2 activation than the other ones.

A New Energy-Saving Catalytic System: Carbon Dioxide Activation by a Metal/Carbon Catalyst.

The conversion of CO2 into useful chemicals is an attractive method to reduce greenhouse gas emissions and to produce sustainable chemicals. However, the thermodynamic stability of CO2 means that a lot of energy is required for its conversion into chemicals. Here, we suggest a new catalytic system with an alternative heating system that allows minimal energy consumption during CO2 conversion. In this system, electrical energy is transferred as heat energy to the carbon-supported metal catalyst. Fast ramping rates allow high operating temperatures (Tapp =250 °C) to be reached within 5 min, which leads to an 80-fold decrease of energy consumption in methane reforming using CO2 (DRM). In addition, the consumed energy normalized by time during the DRM reaction in this current-assisted catalysis is sixfold lower (11.0 kJ min-1 ) than that in conventional heating systems (68.4 kJ min-1 ).