Performance For CO2 Conversion Research Articles

Rationally design and in-situ fabrication of ultrasmall pomegranate-like CdIn2S4/ZnIn2S4 Z-scheme heterojunction with abundant vacancies for improving CO2 reduction and water splitting

Exploring efficient and robust CO2 photoreduction and water splitting photocatalysts are critical for closing the anthropogenic carbon cycle and developing H2 energy source. Herein, ultrasmall pomegranate-like Z-scheme CdIn2S4/ZnIn2S4 heterojunctions with abundant vacancies were rationally designed and in-situ constructed though L-cysteine assisted solvothermal method with precipitation conversion strategy. The obtained CdIn2S4/ZnIn2S4-3 photocatalyst displays the highest performance in the photocatalytic conversion of CO2 and H2O into CO and H2 with yields of 1194.5 and 475.7 μmolg−1h−1, respectively, which increase respectively by 62.2% and 123.1% compared to CdIn2S4 under the visible light irradiation. In addition, CdIn2S4/ZnIn2S4-4 hybrid exhibits excellent stability and activity during the 23-hour continuous HER, the average yield of H2 in 23-hour is up to 10286.6 μmolg−1h−1. This study provides a practical method for in-situ fabrication of ultrasmall pomegranate-like Z-scheme nano-heterostructures with abundant vacancies, which are valuable for efficient and robust implementation in a wide range of environmental and energy applications.

Boosting CO2 methanation on ceria supported transition metal catalysts via chelation coupled wetness impregnation

The incipient wetness impregnation (IWI) method is widely used in the preparation of supported transition metal catalysts for its high throughput and cost-effective synthesis, yet suffers from poor metal-support interaction, restricting its further application at an industrial scale. Herein, a universal strategy of chelation coupled impregnation (CCI) is presented. The as-prepared Ni/CeO2(CCI) showed superior catalytic performance for CO2 conversion (84.3%) and CH4 selectivity (100%) under the experimental conditions (WGHSV = 24,000 mL g−1 h−1 and H2/CO2 = 4:1) even at low temperatures (T = 275 °C). The surface characterization results confirmed that the agglomeration of metal active sites in Ni/CeO2(CCI) was restricted and more surface oxygen vacancies were generated on CeO2. Further, the in-situ diffuse reflectance infrared Fourier transform spectroscopy (in-situ DRIFTS) analysis suggested that the surface oxygen vacancies that served as active sites could facilitate the direct dissociation of CO2 more favorably than the associative route, thus significantly promoting CO2 methanation activity.

Ag@Pd bimetallic structures for enhanced electrocatalytic CO2 conversion to CO: an interplay between the strain effect and ligand effect.

Electrochemical CO2 reduction reactions provide a promising path to effectively convert CO2 into valuable chemicals and fuels for industries. Among the many CO2 conversion catalysts, Pd stands out as a promising catalyst for effective CO2 to CO conversion. Here, using the misfit strain strategy, Ag@Pd bimetallic nanoparticles with different Pd overlayer contents were prepared as CO2 reduction catalysts. By varying the Pd overlayer content, all the Ag@Pd bimetallic nanoparticles exhibited superior CO2 conversion performance over their Pd and Ag nanoparticle counterparts. An optimal Pd-to-Ag ratio of 1.5 : 1 yielded the highest CO faradaic efficiency of 94.3% at -0.65 V vs. RHE with a high CO specific current density of 3.9 mA cm-2. It was found that the Pd content can substantially affect the interplay between the strain effect and ligand effect, resulting in optimized binding properties of the reaction intermediates on the catalyst surface, thereby enhancing the CO2 reduction performance.

Sustained CO2-photoreduction activity and high selectivity over Mn, C-codoped ZnO core-triple shell hollow spheres

Solar conversion of CO2 into energy-rich products is one of the sustainable solutions to lessen the global energy shortage and environmental crisis. Pitifully, it is still challenging to attain reliable and affordable CO2 conversion. Herein, we demonstrate a facile one-pot approach to design core-triple shell Mn, C-codoped ZnO hollow spheres as efficient photocatalysts for CO2 reduction. The Mn ions, with switchable valence states, function as “ionized cocatalyst” to promote the CO2 adsorption and light harvesting of the system. Besides, they can capture photogenerated electrons from the conduction band of ZnO and provide the electrons for CO2 reduction. This process is continuous due to the switchable valence states of Mn ions. Benefiting from such unique features, the prepared photocatalysts demonstrated fairly good CO2 conversion performance. This work is endeavoured to shed light on the role of ionized cocatalyst towards sustainable energy production.

Unique Z-scheme carbonized polymer dots/Bi4O5Br2 hybrids for efficiently boosting photocatalytic CO2 reduction

Constructing heterojunctions with matched band semiconductor is regarded as effective strategy to promote high-efficiency photocatalytic CO2 reduction. Herein, 0D/2D direct Z-scheme heterojunction involving carbonized polymer dots and Bi4O5Br2 nanosheets (CPDs/Bi4O5Br2) is designed and fabricated, which effectively facilitate migration and separation efficiency of photogenerated carriers and retain more negative electron reduction potential of CPDs and more positive hole oxidation potential of Bi4O5Br2. Moreover, CPDs promote adsorption of CO2 and intermediate COOH* as well as desorption of product CO. The direct Z-scheme mechanism of CPDs/Bi4O5Br2 is collaboratively confirmed by theory calculation, X-ray photoelectron spectroscopy and time-resolved transient absorption spectroscopy. The 8 wt% CPDs/Bi4O5Br2 exhibits the maximal CO production of 132.42 μmol h−1g−1 under Xe lamp irradiation, 5.43 fold higher than that of Bi4O5Br2 nanosheets. The CPDs with up-conversion properties can broaden light utilization range, so that composite material also show better CO2 conversion performance when excitation wavelength is greater than 580 nm.

Atomic iridium species anchored on porous carbon network support: An outstanding electrocatalyst for CO2 conversion to CO

Converting CO2 into valuable chemicals using electrocatalysis is an attractive approach for sustainable energy storage and artificial carbon cycle. In this study, atomically dispersed Ir species (Ad-Ir) that are supported on three-dimensional (3D) porous carbon networks are proposed as electrocatalysts for highly efficient CO2 conversion. The resulting catalysts can preferentially and rapidly produce CO with a high Faradaic efficiency of 95.6 % and a very high turnover frequency (TOF) value of 33,365 h−1. Furthermore, it shows no obvious decay in both FE for CO and current density over 20 h of continuous operation. Based on detailed experimental studies and density functional theory (DFT) calculations, such outstanding catalytic performance for CO2 conversion to CO production can be attributed to the structural advantages of 3D network of porous carbon and atomically dispersed Ir species on the 3D carbon support.

Low-Dimensional Nanostructured Photocatalysts for Efficient CO2 Conversion into Solar Fuels

The ongoing energy crisis and global warming caused by the massive usage of fossil fuels and emission of CO2 into atmosphere continue to motivate researchers to investigate possible solutions. The conversion of CO2 into value-added solar fuels by photocatalysts has been suggested as an intriguing solution to simultaneously mitigate global warming and provide a source of energy in an environmentally friendly manner. There has been considerable effort for nearly four decades investigating the performance of CO2 conversion by photocatalysts, much of which has focused on structure or materials modification. In particular, the application of low-dimensional structures for photocatalysts is a promising pathway. Depending on the materials and fabrication methods, low-dimensional nanomaterials can be formed in zero dimensional structures such as quantum dots, one-dimensional structures such as nanowires, nanotubes, nanobelts, and nanorods, and two-dimensional structures such as nanosheets and thin films. These nanostructures increase the effective surface area and possess unique electrical and optical properties, including the quantum confinement effect in semiconductors or the localized surface plasmon resonance effect in noble metals at the nanoscale. These unique properties can play a vital role in enhancing the performance of photocatalytic CO2 conversion into solar fuels by engineering the nanostructures. In this review, we provide an overview of photocatalytic CO2 conversion and especially focus on nanostructured photocatalysts. The fundamental mechanism of photocatalytic CO2 conversion is discussed and recent progresses of low-dimensional photocatalysts for efficient conversion of CO2 into solar fuels are presented.

CO2 conversion promoted by potassium intercalated g-C3N4 catalyst in DBD plasma system

The direct conversion of CO2 to CO and O2 has attracted extensive attention as CO is a key C1 feedstock for chemical synthesis. The CO2 conversion promoted by γ-Al2O3 supported potassium intercalated g-C3N4 (KuCN/AO) catalyst in a packed-bed dielectric barrier discharge (DBD) plasma system was investigated. A coaxial cylinder DBD plasma reactor was used with Cu powder as the high voltage electrode. Reactor temperature showed converse effect on CO2 conversion. As the reactor temperature decreased from 120 ℃ to 50 ℃, CO2 conversion rate and energy efficiency both increased by ca. 50%. After the catalyst was filled into the discharge area, the discharge mode changed from filamentary discharge to the combination of filamentary-surface discharge. The morphology and structure of KuCN was characterized by SEM, XRD, FTIR and XPS. KuCN kept a porous structure and K element distributed uniformly between CN interlayer spacing. In KuCN/AO assisted DBD plasma system, the highest CO2 conversion rate, CO yield and energy efficiency were increased from 11.1%, 10.0% and 9.41% to 19.3%, 18.1% and 20.6% compared with pure DBD/γ-Al2O3 system, respectively. The main mechanism of KuCN assisted enhancing CO2 conversion in packed-bed DBD reactor was analyzed. The larger specific surface area, layers bridging and charge redistribution enabled KuCN/AO to obtain good plasma-catalytic CO2 conversion performance.

Surface hydroxyls mediated CO2 methanation at ambient pressure over attapulgite-loaded Ni-TiO2 composite catalysts with high activity and reuse ability

Here we report a Ni/TiO2 loaded on attapulgite (ATP) composite catalyst with fairly good CO2 conversion performance amd outstanding reusability (up to 80 h re-use circles) at ambient pressure. The composite was prepared by sol-gel method using ATP powder as the matrix to load TiO2 and Ni nanocrystals in an equivalent impregnation process. Catalytic activity of the newly synthesized catalysts was investigated towards hydrogenation of CO2 at atmospheric pressure in varied temperature between 200 and 450 °C. And in the reaction process, the flow rate of CO2 gas was 2.5 mL/min and the concentration ratio of H2 : CO2 is always 4. The GHSV was 30,000 h−1. Among the investigated catalysts, the 8 % Ni-TiO2-ATP catalyst showed preferable activity at 450 ℃. Improved activity and reducibility were found when adding 8 % Ni due to the enhanced CO2 activation compared with the pure TiO2 or ATP matrix, as well as with the other Ni dosages. These improvements were obtained probably due to its higher surface area than TiO2 catalyst, more surface hydroxyls, and better dispersion on the ATP matrix.

Ionic liquid-based electrolytes for CO2 electroreduction and CO2 electroorganic transformation.

CO2 is an abundant and renewable C1 feedstock. Electrochemical transformation of CO2 can integrate CO2 fixation with renewable electricity storage, providing an avenue to close the anthropogenic carbon cycle. As a new type of green and chemically tailorable solvent, ionic liquids (ILs) have been proposed as highly promising alternatives for conventional electrolytes in electrochemical CO2 conversion. This review summarizes major advances in the electrochemical transformation of CO2 into value-added carbonic fuels and chemicals in IL-based media in the past several years. Both the direct CO2 electroreduction (CO2ER) and CO2-involved electroorganic transformation (CO2EOT) are discussed, focusing on the effect of electrocatalysts, IL components, reactor configurations and operating conditions on catalytic activity, selectivity and reusability. The reasons for the enhanced CO2 conversion performance by ILs are also discussed, providing guidance for the rational design of novel IL-based electrochemical processes for CO2 conversion. Finally, the critical challenges remaining in this research area and promising directions for future research are proposed.

Construction of BiO2−x/Bi2O2.75 heterojunction for highly efficient photocatalytic CO2 reduction

Nowadays, using solar energy to convert CO2 into hydrocarbon fuels such as CO and methanol is considered as an attractive approach to alleviate environmental pollution and the energy crisis. However, the easy recombination of photo-generated carriers and holes of photocatalyst is still the main factor that inhibits photocatalytic performance for CO2 conversion. In this study, the BiO[Formula: see text]/Bi2O[Formula: see text] heterojunction complex was successfully synthesized via a facile hydrothermal method. The BiO[Formula: see text]/Bi2O[Formula: see text] heterogeneous catalyst shows greatly improved photocatalytic performance for CO2 reduction, and the CO and CH4 yields obtained on BiO[Formula: see text]/Bi2O[Formula: see text] are 6.8 and 16 times compared with pure BiO[Formula: see text]. The improved photocatalytic performance can be ascribed to the rapid charge separation on BiO[Formula: see text]/Bi2O[Formula: see text] interface, thereby providing a favorable surface with suitable electronic structure for CO2 reduction. Subsequently, a possible photocatalytic mechanism was proposed to explain the improved performance of photocatalytic CO2 reduction.

Charge separation in hybrid metal–organic framework films for enhanced catalytic CO2 conversion

A three-dimensional porous metal–organic framework-based hybrid film is prepared through a solid conversion process, demonstrating high photocatalytic performance for CO2 conversion under mild conditions.

Plasma-induced black bismuth tungstate as a photon harvester for photocatalytic carbon dioxide conversion

The Bi QDs are reduced in situ on the surface of black Bi2WO6 nanosheets using a novel plasma treatment, which shows a superior CO2 conversion performance.

Efficient Electrochemical Reduction of CO2 to CO in Ionic Liquid/Propylene Carbonate Electrolyte on Ag Electrode

The electrochemical reduction of CO2 is a promising way to recycle it to produce value-added chemicals and fuels. However, the requirement of high overpotential and the low solubility of CO2 in water severely limit their efficient conversion. To overcome these problems, in this work, a new type of electrolyte solution constituted by ionic liquids and propylene carbonate was used as the cathodic solution, to study the conversion of CO2 on an Ag electrode. The linear sweep voltammetry (LSV), Tafel characterization and electrochemical impedance spectroscopy (EIS) were used to study the catalytic effect and the mechanism of ionic liquids in electrochemical reduction of CO2. The LSV and Tafel characterization indicated that the chain length of 1-alkyl-3-methyl imidazolium cation had strong influences on the catalytic performance for CO2 conversion. The EIS analysis showed that the imidazolium cation that absorbed on the Ag electrode surface could stabilize the anion radical (CO2•−), leading to the enhanced efficiency of CO2 conversion. At last, the catalytic performance was also evaluated, and the results showed that Faradaic efficiency for CO as high as 98.5% and current density of 8.2 mA/cm2 could be achieved at −1.9 V (vs. Fc/Fc+).

Robust route to highly porous graphitic carbon nitride microtubes with preferred adsorption ability via rational design of one-dimension supramolecular precursors for efficient photocatalytic CO2 conversion

Abstract The ability to create well-ordered graphitic carbon nitride (g-C3N4) assemblies with good surface adsorption for CO2 represents an important endeavor towards achieving high photocatalytic CO2 reduction activity that yet remains a significant challenge. Herein, a simple yet robust double-solvent-induced self-assembly strategy is, for the first time, developed to yield supramolecular precursors using a single monomer for crafting one-dimensional (1D), highly porous g-C3N4 microtubes that possess remarkable photocatalytic CO2 conversion performance. Intriguingly, the introduction of water and isopropanol triggers the self-assembly of dicyandiamide under hydrothermal conditions to form a melamine-cyanaurate-like complex (MCC) composed of 1D hexagon-shaped, micron-sized crystals with outstanding thermal stability. Subsequent thermal pyrolysis converts these pillar-like crystals into 1D mesoporous g-C3N4 microtubes (denoted MCNM) comprising well-packed nano-leaf-like frameworks (i.e., hierarchical structure). Such unique microtubes are oxygen-doped g-C3N4 and mechanically stable, exhibiting improved visible-light harvesting ability, enhanced charge transfer, increased active sites, and preferred adsorption and activation for CO2, as revealed by a suite of characterization techniques. Consequently, in sharp contrast to bulk g-C3N4, the MCNM manifests a markedly improved photocatalytic activity with a CO evolution rate of 45.16 μmolh−1, reflecting an 11.0-fold enhancement and an apparent quantum efficiency of 2.55% at 420 nm. As such, the double-solvent-induced self-assembly may stand out an effective route to organized supramolecular precursors for preparing hierarchically structured g-C3N4 for efficient photocatalysis.

Porous organic polymers containing zinc porphyrin and phosphonium bromide as bifunctional catalysts for conversion of carbon dioxide

Cycloaddition reaction using CO2 as a starting material to form a cyclic carbonate has been applied to chemical fixation of CO2. In order to further increase the reaction efficiency, herein, a bifunctional catalyst (CPBrs) containing metalloporphyrin and quaternary phosphonium salt groups was prepared, and the related catalytic performance for CO2 conversion was also studied. The catalytic system possesses multiple active sites of zinc porphyrin (Lewis acids) and quaternary phosphonium bromide salts (nucleophilic reagents), which can cooperatively work together to enhance the efficiency of cycloaddition reaction. At the same time, CPBrs (CPBr-1 and CPBr-2) are microporous polymers with permanent microporous pore structure and high specific surface areas (342–370 m2 g−1). Their moderate capacities (5.76 and 8.81% at 1 bar/273 K) to capture carbon dioxide were also beneficial for CO2 conversion. The activity of the bifunctional catalyst is higher than that of the catalyst with a single component. The corresponding highest yield to catalyze cycloaddition reaction between methyl substituented propylene oxide and CO2 is up to 95% (2.5 MPa, 90 °C). What is more, the porous nature of catalysts provides the recoverability of the catalyst, and the efficiency of the catalyst CPBr-2 remains high (above 90% yield) after five catalytic recycle.

High-efficiency CuCe(rod) catalysts for CO2 hydrogenation with high Cu content

Cu catalysts have been widely used in CO2 utilization due to their low reduction temperature and excellent CO2 hydrogenation performance. It is important to well design Cu catalyst with high efficiency and durability for CO2 hydrogenation. In this work, CuCe(rod) catalysts with various Cu contents were prepared. The physicochemical properties of the CuCe(rod) catalysts were described by XRD, TEM, N2-physisorption and H2-TPR.The effect of Cu content on catalytic performance of CO2 hydrogenation with CuCe(rod) catalysts was also studied. Results showed that a high Cu content enhanced CO2 conversion. The 40CuCe(rod) catalyst exhibited the best CO2 conversion performance. At the reaction temperature of 400 °C, the CO production rate (CO2 conversion) and CO selectivity based on the 40CuCe(rod) catalyst could reach 1.69 mol/gcat/h (41.1%) and nearly 100%, respectively. The analysis of kinetic measurements revealed that the activation energy of the 40CuCe(rod) catalyst was lower than that of other catalysts with different Cu contents during a reverse water–gas shift reaction. The lower activation energy and the interface structure of Cu-Ox-Ce were closely related to CO2 hydrogenation activity and remarkable stability for 96 h with minimal loss of CO2 conversion activities.

Control of the pH for marine microalgae polycultures: A key point for CO2 fixation improvement in intensive cultures

Recently, CO2 recycling for the production of valuable microalgae has acquired substantial interest. Most studies investigating CO2 conversion efficiency in algal cultures were based on single species, although a stabilising effect of algal diversity on biomass production was recently highlighted. However, addition of CO2 into polyalgal cultures requires a careful control of pH; performance of CO2 conversion, growth and carbon biomass production are affected by pH differently, depending on the species of microalgae. This study investigates the efficiency of CO2 conversion by natural marine algal assemblage cultivated in open, land-based raceways (4.5 m3, 10 m2), working as high rate algal ponds (HRAP). Ponds were enriched with nitrogen and phosphate, pure CO2 was added and algal cultures were grown under three different fixed pH levels: pH 6, 7 and 8. The highest conversion of photosynthetically fixed CO2 into carbon biomass (40 %) was reached at pH 7, an intermediate level, due to the partial CO2 asphyxiation of algal predators (copepods, ciliates), while being under the suboptimal conditions for the development of marine amoebae. Under this pH, the theoretical maximal biological conversion of available CO2 into carbon biomass was estimated to be 60 % in naturally inoculated open ponds.

Effective Driving of Ag-Loaded and Al-Doped SrTiO3 under Irradiation at λ > 300 nm for the Photocatalytic Conversion of CO2 by H2O

Al-doped strontium titanite (Al–SrTiO3) containing numerous stepwise edges on the surface was found to exhibit an excellent performance in the photocatalytic conversion of CO2 by H2O as an electron...

B-O Bonds in Ultrathin Boron Nitride Nanosheets to Promote Photocatalytic Carbon Dioxide Conversion.

Limited by the chemical inertness of CO2 and the high dissociation energy of the C═O bond, photocatalytic CO2 conversion is highly challenging. Herein, we prepare ultrathin oxygen-modified h-BN (O/BN) nanosheets containing B-O bonds. On the O/BN surface, CO2 can be chemically captured and is bonded with the B-O bond, leading to the formation of an O-B-O bond. This new chemical bond acting as an electron-delivery channel strengthens the interaction between CO2 and the surface. Thus, the reactants can continuously obtain electrons from the surface through this channel. Therefore, the majority of gaseous CO2 directly converts into carbon active species that are detected by in situ DRIFTS over O/BN. Moreover, the activated energies of CO2 conversion are significantly reduced with the introduction of the B-O bond evidenced by DFT calculations. As a result, O/BN nanosheets present an enhanced photocatalytic CO2 conversion performance with the H2 and CO generation rates of 3.3 and 12.5 μmol g-1 h-1, respectively. This work could help in realizing the effects of nonmetal chemical bonds in the CO2 photoreduction reaction for designing efficient photocatalysts.