Performance For CO2 Conversion Research Articles

Investigation of highly efficient CO2 hydrogenation at ambient conditions using dielectric barrier discharge plasma

The increasing utilization of CO2 for synthesizing high-value fuels or essential chemicals is a potentially effective approach to mitigating global warming and climate change. Compared to thermal catalytic CO2 conversion under hash operating conditions (400–500°C, 10 ​MPa), non-thermal plasma can overcome kinetic barriers and trigger reactions beyond thermal equilibrium at ambient temperature and pressure. In this study, the effects of operating conditions (discharge frequency, input power, and gas flow rate) and geometrical parameters (discharge length, discharge gap, and dielectric materials) have been extensively analyzed using typical cylindrical dielectric barrier discharge (DBD) plasma. The discharge characteristics changed by operating conditions (including waveforms of applied voltage and current) are compared, indicating higher applied voltage and lower gas flow rate can strengthen the filamentary discharges. The results demonstrate CO2 conversion rate increases with the increase of applied voltage and the decrease of CO2/H2 ratio, achieving its maximum value of 43.0% at 20 ​mL/min. The highest energy efficiency of 3771.9 ​μg/kJ for CO generation is obtained at the applied voltage of 5.5 ​kV and gas flow rate of 40 ​mL/min, respectively. Besides, the constructure of plasma reactor also impacts the performance of CO2 conversion. On the one hand, the discharge gap has a significant role in the variation of CO2 conversion and product selectivity, which is attributed to the electric field density and corresponding electron-induced reaction. On the other hand, the circulating water-cooling jacket was used to find out the influence of reaction temperature, which switched the product from CO to CH4. This work will pave the way for a sustainable alternative towards future CO2 conversion and utilization.

Unraveling the roles of atomically-dispersed Au in boosting photocatalytic CO2 reduction and aryl alcohol oxidation

Atomically-dispersed metal-based materials represent an emerging class of photocatalysts attributed to their high catalytic activity, abundant surface active sites, and efficient charge separation. Nevertheless, the roles of different forms of atomically-dispersed metals (i.e., single-atoms and atomic clusters) in photocatalytic reactions remain ambiguous. Herein, we developed an ethylenediamine (EDA)-assisted reduction method to controllably synthesize atomically dispersed Au in the forms of Au single atoms (AuSA), Au clusters (AuC), and a mixed-phase of AuSA and AuC (AuSA+C) on CdS. In addition, we elucidate the synergistic effect of AuSA and AuC in enhancing the photocatalytic performance of CdS substrates for simultaneous CO2 reduction and aryl alcohol oxidation. Specifically, AuSA can effectively lower the energy barrier for the CO2→*COOH conversion, while AuC can enhance the adsorption of alcohols and reduce the energy barrier for dehydrogenation. As a result, the AuSA and AuC co-loaded CdS show impressive overall photocatalytic CO2 conversion performance, achieving remarkable CO and BAD production rates of 4.43 and 4.71 mmol g−1 h−1, with the selectivities of 93% and 99%, respectively. More importantly, the solar-to-chemical conversion efficiency of AuSA+C/CdS reaches 0.57%, which is over fivefold higher than the typical solar-to-biomass conversion efficiency found in nature (ca. 0.1%). This study comprehensively describes the roles of different forms of atomically-dispersed metals and their synergistic effects in photocatalytic reactions, which is anticipated to pave a new avenue in energy and environmental applications.

In Situ Oxidative Ring-Opening of Calix[8]arene to Construct Stable Bismuth-Oxo Clusters with Exposed Catalytic Sites for Specific Electroreduction of CO2 to HCOOH.

Nanocluster catalysts typically face challenges in balancing stability with catalytic efficiency. This study introduces a unique bismuth-oxo cluster, solely protected by two ring-opened calixarenes, which demonstrates not only enhanced structural stability but also superior catalytic performance in the sustained conversion of CO2 to HCOOH via electrocatalysis. For the first time, we reveal that under specific solvothermal conditions, tert-butylcalix[8]arene (TBC[8]) can undergo in situ oxidative cleavage of its C-C bond, leading to ring-opened polyphenolic molecules. These molecules serve as protective ligands for the bismuth-oxo cluster, bestowing exceptional structural stability and offering a more flexible and diverse configuration compared to intact TBC[8]. This adaptability promotes the exposure of active bismuth sites on the cluster surface, enhancing catalytic efficiency. Notably, the Bi10 cluster, featuring a monobismuth active site, achieves an exceptional formate production efficiency of 98.79% at -1.25 V vs RHE while maintaining superb durability over 8 h. The stability and catalytic processes of Bi10 surpass those of the Bi13 cluster, which is structurally reinforced by two intact TBC[8] molecules and stabilized by four benzoic ligands. Through in situ infrared spectroscopy and density functional theory calculations, we demonstrate that the monobismuth active site in Bi10 more effectively stabilizes the *OCHO intermediate, thereby promoting the electrocatalytic reduction of CO2 to HCOOH compared to Bi13. This comparative performance underscores the potential of ring-opened calixarene ligands in enhancing the functionality of nanocluster catalysts.

Molecular Engineering of Poly(Ionic Liquid) for Direct and Continuous Production of Pure Formic Acid from Flue Gas.

Electrochemical CO2 reduction reaction (CO2RR) offers a promising approach to close the carbon cycle and reduce reliance on fossil fuels. However, traditional decoupled CO2RR processes involve energy-intensive CO2 capture, conversion, and product separation, which increases operational costs. Here, we report the development of a bismuth-poly(ionic liquid) (Bi-PIL) hybrid catalyst that exhibits exceptional electrocatalytic performance for CO2 conversion to formate. The Bi-PIL catalyst achieves over 90% Faradaic efficiency for formate over a wide potential range, even at low 15% v/v CO2 concentrations typical of industrial flue gas. The biphenyl in PIL backbone affords hydrophobicity while maintaining high ionic conductivity, effectively mitigating the flooding issues. The PIL layer plays a crucial role as a CO2 concentrator and co-catalyst that accelerates the CO2RR kinetics. Furthermore, we demonstrate the potential of Bi-PIL catalysts in a solid-state electrolyte (SSE) electrolyzer for the continuous and direct production of pure formic acid solutions from flue gas. Techno-economic analysis suggests that this integrated process can produce formic acid at a significantly reduced cost compared to the traditional decoupled approaches. This work presents a promising strategy to overcome the challenges associated with low-concentration CO2 utilization and streamline the production of valuable liquid fuels and chemicals from CO2.

Constructing type II heterojunction of 2D/1D Pg-C3N4/Ag3VO4 nanocomposite with high interfacial charge separation for boosting photocatalytic CO2 reduction under solar energy

The well-designed, template-free synthesis of 2D protonated g-C3N4 nanosheets (Pg-C3N4) coupled with novel 1D Ag3VO4 nanorods has been investigated to construct 2D/1D interface heterostructures with strong electrostatic interactions between the positively charged 2D Pg-C3N4 nanosheets and the negatively charged 1D Ag3VO4 nanorods. The coupling of Pg-C3N4 and Ag3VO4 with desirable characteristics resulted in a 2D/1D interface heterojunction with a type II charge carrier transfer mechanism, effectively maintaining and utilizing charge carriers. The 2D/1D Pg-C3N4/Ag3VO4 exhibited remarkable photocatalytic performance for CO2 conversion with H2O, resulting in maximum CH4 and dimethyl ether (DME) production of 352.3 and 130.9 µmol/g-cat, respectively. A quantum yield of 0.23 % for CH4 generation was achieved over the 2D/1D Pg-C3N4/Ag3VO4, which was 2.9 and 1.4 times higher than that of the Pg-C3N4 and Ag3VO4 samples, respectively. The improvement in photocatalytic performance primarily stems from the effective interaction between Pg-C3N4 and ternary Ag3VO4, leading to enhanced transfer and separation of photoinduced charge carriers through the creation of a type II heterojunction. The findings of this study are useful in designing template-free heterojunctions for photocatalytic CO2 conversion and other solar energy applications.

Photocatalytic performance of metal poly(heptazine imide) for carbon dioxide reduction

Poly(heptazine imide) (PHI), a carbon nitride polymer, is a highly efficient visible-light-driven photocatalytic material. We aimed to improve its photocatalytic performance for CO2 conversion. We prepared M-PHIs by encapsulating different metals (M = K, Li, Rb, and Na) and H-PHIs, in which the metal of each M-PHI was ion-exchanged with a proton. We evaluated their photocatalytic activities for CO2 conversion and found that Na-PHI and H-PHI, prepared from Na-PHI (H-PHI(NaCl)), showed more than twice the CO production efficiency of melon and other PHIs.The high CO production efficiency of Na-PHI and H-PHI(NaCl) was attributed to their extremely smaller particle size compared with those of the other PHIs. By closely examining the synthesis conditions of Na-PHI, we have identified a method to intentionally synthesize M-PHI with small particle size. These results provide a new strategy for highly efficient CO2 conversion using PHI.

High-performance photocatalytic reduction of CO2 to CO by defective g-C3N4/CeO2 under sacrificial agent-free conditions☆

Solar energy can be used to convert CO2 into valuable chemical compounds. However, the low activity of photocatalysts has hindered their development. By using defective g-C3N4/CeO2 heterojunctions, CO2 was successfully photo-reduced with high performance under ambient water vapor conditions without adding additives. g-C3N4 in this system has a significant impact on CO2 conversion efficiency, with 5 wt% g-C3N4/CeO2 exhibiting competitive performance, achieving 45.66 μmol/g CO in 6 h with nearly 100% selectivity. Photoactivity is attributed to the formation of g-C3N4/CeO2 heterojunctions, which provide excellent electron transport and electron-hole separation. Additionally, light enhances the CO2 adsorption capacity of the catalyst, thereby improving reaction properties. The photogenerated electrons generated under light excitation can quickly gather at the surface and defective parts of the sample, facilitating effective CO2 adsorption and promoting the formation of *COOH, thus promoting the photoreduction process of CO2. Cycle tests also demonstrate long-term stability. Highly efficient charge separation and reduced free energy of CO2 reduction both promote CO2 conversion performance. This work can provide an important idea for designing CeO2-based CO2 photocatalysts.

Modified TiO2/In2O3 heterojunction with efficient charge separation for visible-light-driven photocatalytic CO2 reduction to C2 product

Utilizing sunlight to convert CO2 into chemical fuels could address the greenhouse effect and fossil fuel crisis. Heterojunction structure catalysts with oxygen vacancy are attractive in the field of photocatalytic CO2 conversion. Herein, a modified TiO2/In2O3 (R-P25/In2O3−x) type II heterojunction composite with oxygen vacancies is designed for photocatalytic CO2 reduction, which exhibits excellent CO2 reduction activity, with a C2 selectivity of 56.66% (in terms of Relectron). In situ Fourier-transform infrared spectroscopy (DRIFTS) and time-resolved photoluminescence (TR-PL) spectroscopy are used to reveal the intermediate formation of the photocatalytic mechanism and photogenerated electron lifetime, respectively. The experimental characterizations reveal that the R-P25/In2O3−x composite shows a remarkable behavior for coupling C–C bonds. Besides, efficient charge separation contributes to the improved CO2 conversion performance of photocatalysts. This work introduces a type II heterojunction composite photocatalyst, which promotes understanding the CO2 reduction mechanisms on heterojunction composites and is valuable for the development of photocatalysts.

UiO-n-membrane regulate bifunctional catalysts GaZrOx/SAPO-34@UiO-n improving CO2 conversion to light olefins

Assembling synergistic-functional nanocatalysts is an effective strategy to achieve highly both active and selective conversion of CO2 into light olefins. Herein, the bifunctional GaZrOx/SAPO-34@UIO-n (n = 66, 66-NH2, 67, 67-NH2, 68, 69) catalyst, UiO-n membrane encapsulating monodispersed SAPO-34 zeolite to get the core-shell SAPO-34@UiO-n (S@Un) and then mixed with GaZrOx, is assembled for CO2 hydrogenation to light olefins. The GaZrOx/SAPO-34 shows C2=-C4= selectivity of only 62.1 %, but the selectivity to C2=-C4= reaches 81.8–85.4 % for the GaZrOx/S@Un. Optimizing UiO-n membrane, the GaZrOx/S@U68 exhibits excellent performance for CO2 conversion into light olefins. The selectivity to C2=-C4= reaches 85.4 % at 19.4 % CO2 conversion and 48.1 % CO selectivity. DOS calculations indicates that GaZrOx can effectively promote CO2 hydrogenation. The results reveal the UiO-n membrane-encapsulating-SAPO-34 synergy-enhancing CO2 conversion to light olefins besides the good catalytic matching of GaZrOx to SAPO-34 in the bifunctional catalyst component.

Ultrafast electron transfer at the In2O3/Nb2O5 S-scheme interface for CO2 photoreduction

Constructing S-scheme heterojunctions proves proficient in achieving the spatial separation of potent photogenerated charge carriers for their participation in photoreactions. Nonetheless, the restricted contact areas between two phases within S-scheme heterostructures lead to inefficient interfacial charge transport, resulting in low photocatalytic efficiency from a kinetic perspective. Here, In2O3/Nb2O5 S-scheme heterojunctions are fabricated through a straightforward one-step electrospinning technique, enabling intimate contact between the two phases and thereby fostering ultrafast interfacial electron transfer (<10 ps), as analyzed via femtosecond transient absorption spectroscopy. As a result, powerful photo-electrons and holes accumulate in the Nb2O5 conduction band and In2O3 valence band, respectively, exhibiting extended long lifetimes and facilitating their involvement in subsequent photoreactions. Combined with the efficient chemisorption and activation of stable CO2 on the Nb2O5, the resulting In2O3/Nb2O5 hybrid nanofibers demonstrate improved photocatalytic performance for CO2 conversion.

Mechanism study on CO2 hydrogenation to methanol on Cu5/TiO2 catalyst

Copper clusters supported on TiO2 have demonstrated exceptional performance in catalyzing the reduction of CO2. However, there is a lack of detailed studies on the underlying mechanism. In this study, we employ first-principles thermodynamics and kinetic calculations to unveil the catalytic reduction mechanism of CO2 to C1 product on the Cu5/TiO2 catalyst. Our calculations reveal that the interaction between the cluster and the support significantly enhances the chemical adsorption of CO2 and lowers the dissociation barrier of H2, creating favorable conditions for hydrogenation reduction of CO2. Additionally, our findings suggest that the Cu5 cluster also significantly enhances the adsorption of *CO intermediates, resulting in a preference for the RWGS pathway over the formate pathway for CO2 reduction. The rate-determining barrier for CH3OH formation is considerably lower than that for CH4 formation, indicating that Cu5/TiO2 exhibits remarkable CO2 conversion performance with nearly 100 % selectivity towards CH3OH production.

Effective CO2 photoreduction to methane over Bi2MoO6/ Ni, N co-doped TiO2 nano-photocatalyst

Bi2MoO6/Ni–N co-doped TiO2 (BM/Ni–N-T) composite was prepared by a hydrothermal, and subsequently a solvothermal method and used for CO2 photocatalytic conversion under visible light irradiation. The effect of nickel concentration in TiO2 on the photocatalytic properties and the effect of nitrogen-nickel co-doping in TiO2 structure on methane production were investigated. Furthermore, the effect of constructing a heterojunction structure between modified TiO2 and Bi2MoO6 semiconductors on the photocatalytic performance was investigated. The morphological and structural properties of the samples were characterized by X-ray diffraction, nitrogen adsorption, field emission scanning electron microscopy, Raman spectroscopy, and photoluminescence spectroscopy. Doping nickel with different concentrations in TiO2 structure could result in a narrowing of the bandgap and increase the light absorption capacity in comparison to an undoped TiO2 sample. The results reveal that modification of TiO2 with both of nickel and nitrogen elements leads to higher surface area and narrower bandgap than pure TiO2. Incorporation of nickel and, or nitrogen into TiO2 structure suppresses the CO2 absorption on the catalyst surface and results in enhanced electron-hole separation efficiency compared to pure TiO2. The 3Ni-T sample with 3 wt% nickel shows the optimum methane production among single-doped TiO2 samples. The Ni–N co-doped TiO2 sample exhibits a good response in CO2 conversion, which was nine times higher than that of undoped TiO2. The BM/Ni–N-T photocatalyst exhibits excellent photocatalytic performance for CO2 conversion (67.9 μmol/g), which is several times higher than that of pure TiO2 (3.2 μmol/g). The enhanced composite photocatalytic performance is mainly attributed to nitrogen and nickel co-doping in TiO2 and heterojunction structure, which improves light absorption capacity and charge carrier separation efficiency.

Installing active metal species in a covalent triazine framework for highly efficient and selective photocatalytic CO2 reduction

A phenanthroline-containing covalent triazine framework metalated with Ni sites (Ni-PT-CTF) has been rationally designed and synthesized, which shows excellent photocatalytic performance for CO2 conversion into CO under visible light irradiation.

Synthesis of “all-in-one” hypercrosslinked organic polymers: experimental and kinetic models for CO2 chemical fixation and iodine adsorption

A series of “all-in-one” hypercrosslinked polymers have been constructed by Friedel–Crafts alkylation and quaternization reactions, which exhibit superior CO2 conversion performance and effective iodine adsorption capacity.

Porous organic polymer containing Tröger’s base skeleton and crown ether for cycloaddition of CO2 and efficient iodine vapor adsorption

A wide range of templating reagents containing crown ether-based Tröger's base structure and coordinating of various co-catalysts were synthesized by polymerization, and characterized using various analytic techniques. Their catalytic performance for CO2 conversion and adsorption properties for iodine vapor were examined. Delightfully, after CETB-X recognized with HBr, all exhibited excellent catalytic activity in the presence of cetyltrimethylammonium bromide. The best-performing catalyst could convert CO2 into cyclic carbonate with a yield of 93.1% under optimal reaction conditions. Furthermore, CETB-C16Br/C16N+Br- possessed excellent stability and substrate suitability with six times without any significant loss of catalytic activity. A preliminary kinetic study was investigated using CETB-C16Br/C16N+Br- and the activation energy has been calculated to be 41.51 kJ/mol. All of these polymers also exhibited iodine adsorption capacities above 3.0 g/g, with the most powerful adsorption reaching 4.68 g/g. Through kinetic simulations, the adsorption process was simulated as a pseudo-first-order kinetic model.

Interfacial Mo-S bond-reinforced hierarchical S-scheme heterostructure of Bi2MoO6@ZnIn2S4 for highly-selective and efficient CO2 photoreduction into CO

Developing highly-selective and efficient photocatalysts for converting CO2 into carbon-based fuels by solar energy is desirable, whereas it is still a severe challenge. Herein, we present a unique interfacial Mo-S bond-bridged hierarchical S-scheme heterostructured photocatalysts, prepared by in-situ loading ZnIn2S4 nanoflakes (ZIS-NFs) on the Bi2MoO6 porous micro-spheres (BMO-PMs) assembled from numerous nanosheets. The interfacial Mo-S bonds can reinforce the separation and migration of photoinduced charge carriers via the S-scheme mechanism in the BMO@ZIS heterostructure. Besides, its hierarchical heterostructure can improve the visible-light response ability, and afford plenty of active sites so as to benefit the CO2 adsorption and activation. Specifically, the combined results of experiment and density functional theory (DFT) calculations indicate that the fine heterostructure can not only convert the endoergic rate-determining step of bare ZIS (namely, CO2* hydrogenation to form COOH*) to an exoergic reaction process and lower the overall activation energy barrier, but also boost the desorption of CO* from the ZIS surface. As a result, in existence of H2O vapor without any sacrificial agents, the optimum photocatalyst (BMO@ZIS-0.4) manifests the outstanding CO2 photoreduction activity, with a CO yield and selectivity of 23.11 μmol g−1h−1 and 93.1 %, respectively, higher than those of the most reported photocatalysts. This work offers an in-depth insight for fabricating the interfacial chemical bond-modulated hierarchical S-scheme heterostructure with a remarkable performance of CO2 conversion.

Prospective life cycle assessment of CO2 conversion by photocatalytic reaction

CO2 conversion is gradually seen as a better way for society to effectively use carbon sources and avoid climate crisis associated with fossil CO2 emissions. And the decision to deploy CO2 technology scale should be relied on its environmental impact. In this work, life cycle assessment model evaluates the environmental performance of CO2 conversion by photocatalytic reaction process with two different catalysts (NiAl-LDH and Co-ZIF-9). Six impact categories considered in this analysis, including climate change, acidification potential, depletion of abiotic resources, eutrophication potential, ozone layer depletion potential, and photochemical oxidation potential. Results indicated that CO2 conversion with Co-ZIF-9 photocatalyst has a better environmental impact than the NiAl-LDH photocatalyst route. Moreover, the Co-ZIF-9 catalyst scenario also has a lower total environmental burden than the conventional CO production route. Sensitivity analysis shows that recycle performance of the catalyst is highly sensitive to the production process in two scenarios. This study could provide a framework for robust decisions in CO2 conversion by photocatalytic reaction, which is useful for policymakers to decide the feasibility of industrialization.

The influence of dielectric materials on CO2 conversion performance of pulsed micro-gap cylindrical dielectric barrier discharge reactor

Abstract Dielectric barrier discharge (DBD) is a non-thermal plasma technology that shows promise for CO2 conversion. However, its efficiency depends on plasma processing parameters, reactor design, and reactor material. This study focused on the effect of dielectric barrier material on the CO2 conversion performance of a pulsed micro-gap DBD reactor. The results of this study show that the DBD reactor with alumina dielectric produced better CO2 conversion performance than the quartz reactor, with a maximum CO2 conversion of 50.17% compared to 21.91% with the quartz reactor. The DBD reactor with alumina dielectric produced a greater current peak and a higher number of micro-discharges than the quartz reactor, which suggests that the number of micro-discharges plays a dominant role in the CO2 conversion performance of the DBD reactor. The use of high dielectric constant material with high surface roughness could enhance the CO2 conversion performance of pulsed micro-gap DBD reactors.

MXene‐Regulated Metal‐Oxide Interfaces with Modified Intermediate Configurations Realizing Nearly 100% CO2 Electrocatalytic Conversion

AbstractElectrocatalytic CO2 reduction via renewable electricity provides a sustainable way to produce valued chemicals, while it suffers from low activity and selectivity. Herein, we constructed a novel catalyst with unique Ti3C2Tx MXene‐regulated Ag−ZnO interfaces, undercoordinated surface sites, as well as mesoporous nanostructures. The designed Ag−ZnO/Ti3C2Tx catalyst achieves an outstanding CO2 conversion performance of a nearly 100% CO Faraday efficiency with high partial current density of 22.59 mA cm−2 at −0.87 V versus reversible hydrogen electrode. The electronic donation of Ag and up‐shifted d‐band center relative to Fermi level within MXene‐regulated Ag−ZnO interfaces contributes the high selectivity of CO. The CO2 conversion is highly correlated with the dominated linear‐bonded CO intermediate confirmed by in situ infrared spectroscopy. This work enlightens the rational design of unique metal‐oxide interfaces with the regulation of MXene for high‐performance electrocatalysis beyond CO2 reduction.

MXene-Regulated Metal-Oxide Interfaces with Modified Intermediate Configurations Realizing Nearly 100% CO2 Electrocatalytic Conversion.

Electrocatalytic CO2 reduction via renewable electricity provides a sustainable way to produce valued chemicals, while it suffers from low activity and selectivity. Herein, we constructed a novel catalyst with unique Ti3 C2 Tx MXene-regulated Ag-ZnO interfaces, undercoordinated surface sites, as well as mesoporous nanostructures. The designed Ag-ZnO/Ti3 C2 Tx catalyst achieves an outstanding CO2 conversion performance of a nearly 100% CO Faraday efficiency with high partial current density of 22.59 mA cm-2 at -0.87 V versus reversible hydrogen electrode. The electronic donation of Ag and up-shifted d-band center relative to Fermi level within MXene-regulated Ag-ZnO interfaces contributes the high selectivity of CO. The CO2 conversion is highly correlated with the dominated linear-bonded CO intermediate confirmed by in situ infrared spectroscopy. This work enlightens the rational design of unique metal-oxide interfaces with the regulation of MXene for high-performance electrocatalysis beyond CO2 reduction.