Reaction Mechanism Of CO2 Research Articles

Reaction mechanism of CO2 on the surface δ-Pu(1 0 0):a DFT study

This investigation elucidates the adsorptive and dissociative interactions of CO2 and CO molecules with the δ-Pu (100) surface, utilizing state-of-the-art first-principles calculations. The study unearths that the hollow site epitomizes the most favorable adsorption locus for both CO2 and CO. Within the paramount adsorption configuration, there prevails a propensity for both species to partake in dissociative adsorption, characterized by CO2 cleaving into an O atom and a concomitant CO moiety, whereas CO disintegrates into discrete C and O atoms. The dissociation energy barriers conducive to such configurations are computed to be 3.0568 eV for CO2 and 5.1667 eV for CO. A thorough analysis of electronic charges and density of states intimates a transfer of electrons from the Plutonium surface atoms to the carbonaceous adsorbates during dissociation. Post dissociation of the C-O bond, the 6d orbitals of Plutonium engage in electronic hybridization with the 2p orbitals of Carbon, culminating in the constitution of ionic bonding.

Surface species in direct liquid phase synthesis of dimethyl carbonate from methanol and CO2: an MCR-ALS augmented ATR-IR study.

The reaction mechanism of dimethyl carbonate (DMC) production over ZrO2 from CO2 and CH3OH is well-known, but the level of understanding has not improved in the last decade. Most commonly, the reaction mechanism has been explored in the gas phase, whilst DMC production occurs in the liquid phase. To overcome this contradiction, we exploited in situ ATR-IR spectroscopy to study DMC formation over ZrO2 in the liquid phase. A multiple curve resolution-alternate least square (MCR-ALS) approach was applied to spectra collected during the CO2/CH3OH interaction with the catalyst surface, leading to the identification of five pure components with their respective concentration profiles. CO2 and CH3OH activation to carbonates and methoxide species was found to strongly depend on the reaction temperature. Low temperature prevents methanol dissociation leaving a catalyst covered with stable carbonates, whilst higher temperature decreases the stability of the carbonates and enhances the formation of methoxides. A reaction path involving the methoxide/carbonate interaction at the surface was observed at low temperature (≤50 °C). We propose that a different reaction path, independent of carbonate formation and involving the direct CO2/methoxide interplay, occurs at 70 °C.

Gas absorption in reactive solutions: Adapted instrumentation of a stirred cell for kinetic study and application to CO2/amine systems

The elimination of impurities from natural gas (water, CO2, H2S, mercaptans) is an obligation: in Europe, a max. of 20 mg/Sm3 in total sulfur (at 15°C and 1 atm) is allowed, as well as 2.5 vol% in CO2. It maximizes the calorific value of delivered gas and limits chemical risks (corrosion, toxicity) associated with this transition fuel to cleaner energy sources. Acid gas separation is commonly performed by reactive gas-liquid absorption. Raw gas and absorptive solution are brought into counter current contact in an absorber at 40-80°C and 30-80 bar. Then the acid-gas loaded solvent is sent to a stripper where acid gas desorption from the solvent takes place at T between 105 and 140°C and P ≤ 2.5 bar. The solvent is an aqueous base (e.g., amine) solution. A good solvent has a high reactivity with the dissolved gas during absorption and a low regeneration energy, hence the advantage of mixtures of two amines. Here we study an aqueous solution of a small amount of piperazine (PZ) added to methyldiethanolamine (MDEA). PZ reacts faster with CO2 than MDEA, and the major reaction product with CO2 is the hydrogen carbonate ion HCO3-, which lowers the solvent regeneration duty. This work aims at characterising the kinetics of the absorption of CO2 in an aqueous solution of MDEA-PZ. Indeed, no consensus has been found on the reaction mechanism of CO2 in this amine mixture; the synergies between MDEA and PZ observed in the literature remain poorly explained. However, its knowledge is essential to optimize solvent formulation and industrial unit design.

Reaction Mechanism of CO2 with Choline-Amino Acid Ionic Liquids: A Computational Study.

Carbon capture and sequestration are the major applied techniques for mitigating CO2 emission. The marked affinity of carbon dioxide to react with amino groups is well known, and the amine scrubbing process is the most widespread technology. Among various compounds and solutions containing amine groups, in biodegradability and biocompatibility perspectives, amino acid ionic liquids (AAILs) are a very promising class of materials having good CO2 absorption capacity. The reaction of amines with CO2 follows a multi-step mechanism where the initial pathway is the formation of the C-N bond between the NH2 group and CO2. The added product has a zwitterionic character and can rearrange to give a carbamic derivative. These steps of the mechanism have been investigated in the present study by quantum mechanical methods by considering three ILs where amino acid anions are coupled with choline cations. Glycinate, L-phenylalanilate and L-prolinate anions have been compared with the aim of examining if different local structural properties of the amine group can affect some fundamental steps of the CO2 absorption mechanism. All reaction pathways have been studied by DFT methods considering, first, isolated anions in a vacuum as well as in a liquid continuum environment. Subsequently, the role of specific interactions of the anion with a choline cation has been investigated, analyzing the mechanism of the amine-CO2 reaction, including different coupling anion-cation structures. The overall reaction is exothermic for the three anions in all models adopted; however, the presence of the solvent, described by a continuum medium as well as by models, including specific cation- -anion interactions, modifies the values of the reaction energies of each step. In particular, both reaction steps, the addition of CO2 to form the zwitterionic complex and its subsequent rearrangement, are affected by the presence of the solvent. The reaction enthalpies for the three systems are indeed found comparable in the models, including solvent effects.

Photocatalytic reduction of CO2 on BiOX： Effect of halogen element type and surface oxygen vacancy mediated mechanism

Photo-chemical conversion of CO2 into solar fuels by photocatalysts has attracted significant attention. However, poor reaction efficiency remains a huge obstacle. Deep insight into the reaction mechanism of CO2, especially the active site of photocatalyst could provide scientific basis for the development of more efficient photocatalyst. The high inertness of CO2 and the multi-electron reduction feature on a photocatalyst determine high complexity of the reaction for the study. Here, pure Bismuth oxyhalides (BiOX, where X = F, CI, Br, I) with the layered structure, which were synthesized by both hydrothermal method and chemical precipitation method, were selected as model photocatalysts. The photocatalytic behaviors of the samples were evaluated by the CO2 reduction with H2O without the additional photosensitizer and sacrificial agent. The as-prepared BiOBr was observed to exhibit the best CO2 photoreduction performance under the simulated sunlight. The evolution rates of CO and CH4 are 21.6 μmol g−1 h−1 and 1.2 μmol g−1 h−1, respectively. The effects of water dosage, light intensity and irradiation time on the efficiency of CO2 photoreduction were investigated systematically. Interestingly, the reduction selectivity of CO2 to CO almost reaches 100% in the case of high light intensity. By combination with isotopic tracing method, electron spin-paramagnetic resonance (ESR), in-situ Fourier transform infrared (FTIR) characterization, positron annihilation lifetime (PAL) spectra, and Density functional theory (DFT) calculation, the oxygen vacancy mediated mechanism of photoreduction CO2 was suggested for BiOX. This work provides new information and insights to deepen the understanding for defect photocatalysis on CO2 reduction of semiconductor.

Influencing factors and reaction mechanism for catalytic CO2 gasification of sawdust char using K-modified transition metal composite catalysts: Experimental and DFT studies

Gasification of renewable biomass, sawdust char in this study, was carried out with CO2 to observe the effect of the gasification temperature, CO2 adsorption, and K-modified transition metal composite catalysts; this was known as the Boudouard reaction. The catalysts were characterized using inductively coupled plasma-optical emission spectrometry, X-ray photoelectron spectroscopy, X-ray diffraction analysis, BET surface area analysis, and scanning electron microscopy. The reaction mechanism of the catalytic gasification was investigated using thermogravimetry and density functional theory. The results showed that temperature was one of the most important operating variables for char gasification, and carbon conversion increased 2.55 times within 40 min when the temperature increased from 750 °C to 800 °C. Composite catalysts effectively improved the char conversion at low temperatures, and the order of catalytic performance was KCo > KNi > KFe > KCe. The catalytic CO2 gasification activity depended not only on the CO2 quantity adsorbed, but also on the CO2 decomposition activity on the catalyst surfaces. The CO2 reaction mechanism over Co, Ni, and Fe surfaces can be written as follows: M + CO2 → M-Oads + CO, M-Oads + C* → M + CO. Over CeO2 surface, the reaction mechanism was the following: CeO2 + C* → CeO2vacO + CO, CeO2vacO + CO2 → CeO2 + CO. These results can aid in the CO2 catalytic gasification mechanism and provide further theoretical guidance to improve the industrialization of biomass gasification.

Synthesis and Characterization of Degradation‐Resistant Cu@CuPd Nanowire Catalysts for the Efficient Production of Formate and CO from CO2

AbstractNot only are the product selectivity and the activity of electrocatalysts important aspects for the evaluation of their overall performance, but also their stability and resistance against structural and compositional degradation during the electrocatalytic reaction. Palladium nanoparticles (Pd‐NPs) have already been identified as superior electrocatalysts for the electrochemical conversion of CO2 into formate at extremely low overpotentials and into carbon monoxide (CO) at medium overpotentials. However, these catalysts suffer from fast degradation, owing to irreversible CO poisoning of Pd reaction sites. Herein, we report on nanoparticulate bimetallic Pd45Cu55 catalysts, demonstrating a similar selectivity and activity to the pure Pd‐NPs, but showing additional superior degradation stability and resistance against CO poisoning. Pd45Cu55 catalysts were synthesized by means of a galvanic displacement reaction using copper nanowires (Cu‐NWs) as the starting material (template) for the galvanic displacement reaction, which leaves a surface‐confined alloy film and respective nanoparticles on the Cu‐NW template (denoted as Cu@CuPd‐NWs). A faradaic efficiency (FE) up to FEformate ≈80 % can be achieved at −0.3 V vs. RHE, thus clearly proving that the ‘anomalous’ CO2 reaction mechanism via the CO2 hydrogenation pathway, discussed for pure Pd‐NPs, can also be transferred to Pd‐based bimetallic systems. At medium overpotentials, the product selectivity changes from selective formate to predominant CO formation with a maximum faradaic efficiency of FECO=86 %. Extended CO2 electrolyses demonstrate, for both formate and CO production, superior degradation stability, for example, FECO remains at 85 %±5 % for the duration of 20 h. For the first time, identical location high‐angle annular dark‐field scanning transmission electron microscopy (IL‐HAADF‐STEM) in combination with energy‐dispersive X‐ray spectrometry and identical location scanning electron microscopy (IL‐SEM) were applied to demonstrate the compositional and structural stability of the bimetallic catalyst under CO2 reduction conditions.

Insight into gliding arc (GA) plasma reduction of CO2 with H2: GA characteristics and reaction mechanism

As an intermedia between cold and thermal plasmas, warm plasma generated by gliding arc (GA) discharge possesses high conversions and high energy efficiencies for CO2 conversion. However, there is little understanding for the arc characteristics in CO2-based atmosphere and reaction mechanism of CO2 in GA plasma from experimental approach. For this purpose, a magnetically driven GA plasma with a constant length of arc is designed to study GA characteristics and reaction mechanism by changing H2/CO2 molar ratio (from pure CO2 to pure H2). In the entire range of H2/CO2 ratio, the arc channel shows a glow-like feature. The plasma parameters are arc temperature of 2200–3600 K, electron density of ~1.6 × 1014 cm−3 and electron temperature of ~3 eV. From pure CO2 to pure H2, arc diameter decreases from 1.3 to 0.6 mm, whereas rotational frequency increases from 20 to 64 Hz. Based upon the optical emission spectra of CO, OH, H and O species, chemluminescence spectra of CO and O recombination and CO production rate detected online by gas chromatographs, the reaction mechanism at low and high H2/CO2 molar ratios is disclosed.

Absorption of CO2 into novel aqueous bis(3-aminopropyl)amine and enhancement of CO2 absorption into its blends with N-methyldiethanolamine

A study towards the kinetics of carbon dioxide (CO2) absorption into a novel aqueous solution of bis(3-aminopropyle)amine (APA) was carried out at 303, 308, 313 and 323K over a concentration range of 0.1–0.5kmolm−3 and different CO2 partial pressure. The reaction mechanism of CO2 with primary and secondary amines (zwitterionic mechanism) is described and based on this, experimentally obtained kinetic data are interpreted. A qualitative nuclear magnetic resonance [NMR (1D and 2D)] spectroscopy method has been applied to develop the reaction scheme for novel aqueous APA with CO2. The kinetic rate parameters were investigated according to the pseudo-first-order condition. The values of second-order rate constant, k2-APA and reaction rate with CO2 reported in this study were higher than piperazine (PZ), 2-(1-piperazinl)-ethylamine (PZEA), etc. Furthermore, enhancement factor increases significantly in comparison to aqueous MDEA solutions when the APA concentrations in the blends with MDEA varied from 0 to 0.5kmolm−3.

Thermogravimetric analysis of the water vapor addition during the CaO carbonation process at moderate temperatures (40–70 °C)

Experiments were performed on calcium oxide, using water vapor with N2 or CO2 as carrier gases, between 40 and 70 °C. A initial experiment was performed with water vapor in the presence of N2 to elucidate the possible hydroxylation process produced by water vapor exclusively. On the other hand, when CO2 was used as carrier gas the CaO reactivity changed, producing different hydrated, hydroxylated, and carbonated phases. On the basis of these results and the fact that under dry conditions CO2 is not absorbed on CaO at T < 70 °C, a possible CaO–H2O–CO2 reaction mechanism was proposed, where CaO superficial hydroxylation process seems to play a very important role during the CO2 capture. Finally, a kinetic analysis was produced to compare the temperature and humidity relative influence on the whole process.

Kinetics of absorption of carbon dioxide into aqueous potassium salt of proline

The absorption of carbon dioxide (CO2) into aqueous solution of potassium prolinate (KPr) are studied at 303, 313, and 323K within the salt concentration range of 0.5–3.0kmolm−3 using a wetted wall column absorber. The experimental results are used to interpret the kinetics of the reaction of CO2 with KPr for the above mentioned concentration and temperature range. Following the reaction mechanism of CO2 with primary and secondary alkanolamies, the reaction of CO2 with KPr is also described using zwitterionic mechanism. Based on the pseudo-first-order condition for the CO2 absorption, the reaction rate parameters are determined from the kinetic measurements and presented at each experimental condition. The reaction order is found to be in between 1.36 and 1.40 with respect to KPr for the above mentioned concentration range. The second-order rate constants, k2, are obtained as 118,914, 203,851, and 317,625m3kmol−1s−1 at 303, 313, and 323K, respectively with activation energy of 36.5kJmol−1. The second-order rate constants are much higher than for alkanolamines and some other salt of amino acids.

Influence of operating temperature on CO2-NH3 reaction in an aqueous solution

Although aqueous ammonia solution has been focused on the removal of CO2 from flue gas, there have been very few reports regarding the underlying analysis of the reaction between CO2 and NH3. In this work, we explored the reaction of CO2-NH3-H2O system at various operating temperatures: 40 °C, 20 °C, and 5 °C. The CO2 removal efficiency and the loss of ammonia were influenced by the operating temperatures. Also, infrared spectroscopy measurement was used in order to understand the formation mechanism of ion species in absorbent, such as NH2COO−, HCO3−, CO32−, and NH4+, during CO2, NH3, and H2O reaction. The reactions of CO2-NH3-H2O system at 20 °C and 40 °C have similar reaction routes. However, a different reaction route was observed at 5 °C compared to the other operating temperatures, showing the solid products of ammonium bicarbonates, relatively. The CO2 removal efficiency and the formation of carbamate and bicarbonate were strongly influenced by the operating temperatures. In particular, the analysis of the formation carbamate and bicarbonate by infrared spectroscopy measurement provides useful information on the reaction mechanism of CO2 in an aqueous ammonia solution.

Toward Understanding the Effect of Water Sorption on Lithium Zirconate (Li2ZrO3) during Its Carbonation Process at Low Temperatures

Lithium metazirconate with and without potassium were synthesized by solid-state reaction. Different water vapor sorption experiments were performed in the presence and absence of CO2 to elucidate the different physicochemical processes produced. In the absence of CO2, initial results showed that potassium addition enhances significantly the water sorption on the Li2ZrO3 ceramic. Then, it was shown that water vapor is trapped by two different mechanisms on Li2ZrO3, adsorption and absorption. When CO2 was added to water vapor flow the Li2ZrO3 reactivity increased significantly. On the basis of these results, a possible K−Li2ZrO3−H2O−CO2 reaction mechanism was proposed; as a first step Li2ZrO3 and H2O must react producing some Li−OH and Zr−OH species. Then, CO2 must react with hydroxyl species (mainly Li−OH), producing lithium carbonate. Finally, the presence of this new specie must favor a higher water adsorption.

Analysis of the CO2 and NH3 Reaction in an Aqueous Solution by 2D IR COS: Formation of Bicarbonate and Carbamate

The two-dimensional (2D) infrared correlation spectra obtained from the reaction time- and concentration-dependent IR spectra elucidates the reaction of CO2 and NH3 in an aqueous solution for CO2 absorption. In the synchronous 2D correlation spectra, the interrelation of the proton with carbamate and bicarbonate indicates that the pH level affected the formation reactions of the two products. Furthermore, the interrelation of carbamate with bicarbonate confirmed the conversion of carbamate into bicarbonate with the release of protons (or the decrease of the pH). From the experimental results including the asynchronous 2D correlation spectra, the reaction of the CO2 and aqueous ammonia proceeded through the following steps: formation of carbamate, formation of bicarbonate, release of protons, and conversion of carbamate into bicarbonate. The analysis of the formation of carbamate and bicarbonate by 2D infrared correlation spectroscopy provides useful information on the reaction mechanism of CO2 and NH3 in aqueous solutions.