CO2 Conversion Processes Research Articles

Tuning Sb Atoms on Cu‐Based Catalysts for Electrochemical Conversion of CO2 to Syngas

AbstractThe electrochemical CO2RR into syngas provides an attractive way to produce raw materials for synthesizing various value‐added chemicals. However, a wide range of tunable syngas ratio of CO/H2 is hard to achieve during the electrochemical CO2 conversion process. Herein, we propose a facile electrodeposition method for the preparation of Sb modified Cu‐based catalysts with a high activity for the ratio‐tunable production of syngas. The Cu10Sb1 catalyst reaches a high FE of 71% for CO at a potential of −1.09 V versus RHE with the tunable CO/H2 ratio of syngas from ∼0.6 to ∼7.8 at the applied potentials from −0.78 V to −1.09 V. Theoretical calculations reveal the tuning effect of Sb atoms on Cu‐based catalyst for the electrochemical conversion of CO2 to syngas, in which the formation of CO on Sb modified Cu‐based catalyst possesses lower energy barrier in potential‐limiting steps during CO2RR. Meanwhile, the robust charge interaction between COOH* species and the surface of Sb modified Cu‐based catalyst enhances the activity of COOH* species, thus improving FE and current density for conversion into syngas products. This work brings a new strategy for the synthesis of low‐cost syngas catalyst and the tuning effect of metal atom on Cu‐based catalyst for CO2RR.

Photovoltaic Cells and Scintillators Towards Carbon Footprint Reduction: Advantages and Challenges for Ecological Safety

The main goal of this review paper is to show the advantages and challenges of photovoltaic cells/modules/panels and scintillators towards carbon footprint reduction for ecological safety. Briefly, the various types of solar-driven CO2 conversion processes are shown as a new concept of CO2 reduction. The health toxicity and environmental effects of scintillators, along with risks associated with use and disposal, are presented, taking into consideration inorganic and organic materials. Factors affecting the durability and lifespan of scintillators and the carbon footprint of solar cell production are analysed, considering CO2 emission. Moreover, the technology of recycling photovoltaic modules and scintillators, along with a SWOT analysis of scintillation material toxicity, is presented to find the best solutions for clean technology and ecological safety. Finally, we offer recommendations for the areas where the most significant reductions in CO2 emissions are expected to be implemented in the future of green energy in industry, including ESG strategies.

Conversion of CO2 into Synthetic Motor Fuels

The process of CO2 conversion into synthetic hydrocarbons including the stages of synthesis gas production on the catalyst NIAP 06-06 and hydrocarbon synthesis by the Fischer-Tropsch method on a bifunctional zeolite-containing catalyst has been investigated. Experimental studies of the process of catalytic conversion of CO2 into synthesis gas were carried out in order to obtain gas with the ratio of H2/CO close to the required ratio for Fischer-Tropsch synthesis. The possibility of obtaining gasoline and diesel fractions of hydrocarbons with a high content of isomeric structures that increase the performance characteristics of motor fuels has been shown. The yield of hydrocarbons C5+ with 1 m3 of initial CO2 and H2 at the synthesis temperature of 220 °C is found to be 44.5 g.

Exploring the CO2 conversion activated by the dielectric barrier discharge plasma assisted with photocatalyst via machine learning

DBD plasma assisted with halide perovskite photocatalysts is very attractive for the conversion of CO2 into high value-added products under mild conditions. However, it is still challenging to further effectively improve the corresponding CO2 conversion efficiency due to the consumption of time, materials, equipments via traditional experimental approach. In this paper, we simulate the CO2 conversion process under the DBD plasma assisted with different photocatalysts by machine learning. The process conditions and material parameters were selected as the feature variables of the machine learning model, and all the features were screened by combining Pearson's correlation coefficient and MIR ranking. The regression algorithms were evaluated using K-fold cross-validation combined with the coefficient of determination (R2), while SVR and BPANN with the best prediction performance for CO2 conversion ratio and energy efficiency were selected to establish the prediction models. In order to increase the accuracy of predictions, the hyperparameters of these two base models were improved using genetic algorithm, particle swarm optimization and Bayesian optimization. The R2 of the GA-SVR-CO2 and Bayesian-BPANN-EE reached 0.8960 and 0.9679 for the testing sets, respectively, and their practical applications were successfully verified. In addition, the effects of feature parameters on the conversion efficiency were revealed by SHAP. SEI scatter plots and Spearman correlation coefficient have been used for correlation analysis to better explore the correlation between machine learning models and experiments. This work brings new insights into the contributions of multiple parameters in the plasma system assisted with photocatalyst for efficient conversion of CO2.

Sustainable Valorization of CO2 through Nuclear Power-to-X Pathways

Some of the issues concerning energy security and climate change can be addressed by employing nuclear power (NP) to supply the energy required for the conversion of carbon dioxide (CO2) into chemicals, products, and materials. Nuclear energy represents a neutral carbon source that can be generated sustainably, reliably, and consistently. Nuclear power plants (NPPs) could supply energy in the form of heat, electricity, and ionizing radiation to drive CO2 chemical reactions underpinning NP-to-X type of pathways. CO2 conversion processes are either commercially available or emerging technologies at different developmental maturity stages. This work reviews the published literature (articles and patents) that reports R&D results and the understanding and development of chemical reactions and processes, as well as the efforts in integrating NPPs and chemical processes (CPs). As will be made evident, a new industrial era for the manufacturing of decarbonized chemicals, products, and materials will be possible by developing and implementing new (more energy- and carbon-efficient) processes responding to the NP-to-X pathways. This new decarbonizing platform not only contributes to achieving net zero goals but also broadens the NPP product beyond electricity.

Emerging ZnO Semiconductors for Photocatalytic CO2 Reduction to Methanol.

Carbon recycling is poised to emerge as a prominent trend for mitigating severe climate change and meeting the rising demand for energy. Converting carbon dioxide (CO2) into green energy and valuable feedstocks through photocatalytic CO2 reduction (PCCR) offers a promising solution to global warming and energy needs. Among all semiconductors, zinc oxide (ZnO) has garnered considerable interest due to its ecofriendly nature, biocompatibility, abundance, exceptional semiconducting and optical properties, cost-effectiveness, easy synthesis, and durability. This review thoroughly discusses recent advances in mechanistic insights, fundamental principles, experimental parameters, and modulation of ZnO catalysts for direct PCCR to C1 products (methanol). Various ZnO modification techniques are explored, including atomic size regulation, synthesis strategies, morphology manipulation, doping with cocatalysts, defect engineering, incorporation of plasmonic metals, and single atom modulation to boost its photocatalytic performance. Additionally, the review highlights the importance of photoreactor design, reactor types, geometries, operating modes, and phases. Future research endeavors should prioritize the development of cost-effective catalyst immobilization methods for solid-liquid separation and catalyst recycling, while emphasizing the use of abundant and non-toxic materials to ensure environmental sustainability and economic viability. Finally, the review outlines key challenges and proposes novel directions for further enhancing ZnO-based photocatalytic CO2 conversion processes.

Mild one-pot production of glycerol carbonate from CO2 with separation from ionic liquid catalyst

Carbon capture and utilization stands as way forward in the minimization of CO2 emissions. It complements the search for clean and effective energy, as it is challenging to achieve zero to negative CO2 net emissions. The glycerol carbonate product opens a new strategy based on a double-residue approach (glycerol and CO2) to contribute, together with ionic liquids (ILs), drafting a new one-pot concept (intensified three phase reactor) at mild conditions and using homogeneous catalysts. In this work, the catalytic activity of [P666,14][Br] in the cycloaddition of CO2 to glycidol has been demonstrated to be highly effective under mild conditions of 45 °C and 5 bar. In addition, liquid–liquid extraction approach is found to be an efficient separation strategy for carbonate product and IL catalyst. 1-Decanol (DOH) is selected as efficient extracting solvent, due to its almost complete immiscibility with glycerol carbonate, as well as the high distribution ratio of the IL catalyst in DOH rich phase. It implies an easy product separation and, simultaneously, an easy catalyst recovery. A preliminary kinetic validation of the three-phase reactor performance has been properly described, enabling the intensified concept. Finally, combining COSMO/Aspen simulation and life cycle assessment (LCA) methodologies, low energy consumption (avoiding heating) and low GWP scenarios for the CO2 conversion process have been concluded. This work enables a new concept together with concluding the path to developing this CCU technology in the search of zero to negative CO2 emissions to sustainably capture and convert CO2 into value-added products.

Ru Single Atom Dispersed Cu Nanoparticle with Dual Sites Enables Outstanding Photocatalytic CO2 Reduction.

Cu-based catalysts are promising candidates for CO2 reduction owing to the favorable energetics of Cu sites for CO2 adsorption and transformation. However, CO2 reduction involving insurmountable activation barriers and various byproducts remains a significant challenge to achieve high activity and selectivity. Herein, a photocatalyst constructed with single-Ru-site-on-Cu-nanoparticle on Bi4Ti3O12 exhibits exceptional activity and selectivity for CO2 conversion to CO. The experimental and theoretical results consistently reveal that the Ru-Cu dual sites allow the rapid transfer of photogenerated carriers for closely interacting with CO2 molecules. Importantly, the Ru-Cu dual sites exhibit extremely strong CO2 adsorption ability, and the Gibbs free energy of the rate-determining step (*CO2 to *COOH) has been significantly reduced, synergistically enhancing the entire CO2 conversion process. The optimal BTOCu2Ru0.5 photocatalyst manifests a high performance for selective reduction of CO2 to CO, yielding 10.84 μmol over 15 mg of photocatalyst in 4 h (180.67 μmol·g-1·h-1) under a 300 W Xe lamp without any photosensitizer and sacrificial reagent, outperforming all bismuth-based materials and being one of the best photocatalysts ever reported under similar reaction conditions. This work presents a strategy for the rational design of multiple metal sites toward efficient photocatalytic reduction of CO2.

Surface-Integrating Oxygen Vacancy and CuxO Nanodots Enabling Synergistic Electric Field and Dual Catalytic Sites Boosting CO2 Photoreduction.

High carrier separation efficiency and rapid surface catalytic reaction are crucial for enhancing catalytic CO2 photoreduction reaction. Herein, integrated surface decoration strategy with oxygen vacancies (Ov) and anchoring CuxO (1 < x < 2) nanodots below 10nm is realized on Bi2MoO6 for promoting CO2 photoreduction performance. The charge interaction between Ov and anchored CuxO enables the formation of enhanced internal electric field, which provides a strong driving force for accelerating the separation of photocharge carriers on the surface of Bi2MoO6 (ηsurf ≈71%). They can also cooperatively reduce the surface work function of Bi2MoO6, facilitating the migration of carrier to the surface. Meanwhile, surface-integrated Ov and CuxO nanodots allowing dual catalytic sites strengthens the adsorption and activation CO2 into *CO2 over Bi2MoO6, considerably boosting the progression of CO2 conversion process. In the absence of co-catalyst or sacrificial agent, Bi2MoO6 with Ov and CuxO nanodots achieves a photocatalytic CO generation rate of 12.75µmol g-1 h-1, a remarkable increase of over ≈15 times that of the original counterpart. This work provides a new idea for governing charge movement behaviors and catalytic reaction thermodynamics on the basis of synergistic improvement of electric field and active sites by coupling of the internal defects and external species.

Potential of eNose Technology for Monitoring Biological CO2 Conversion Processes

Potential of eNose Technology for Monitoring Biological CO2 Conversion Processes

Sorption-enhanced ethanol steam reforming coupled with in-situ CO2 capture and conversion

The impacts of climate change and the issue of greenhouse gas emissions have sparked research into renewable energy alternatives to fossil fuels. Hydrogen has gained attention as a clean, renewable and environmentally friendly energy source. Enhanced-ethanol steam reforming has been proposed as a promising method for blue hydrogen production, addressing greenhouse gas emission issues. The use of catalysts enhances the adsorption of ethanol and water molecules on the surface, promoting the reaction rate. This study systematically explored the effects of different Fe loading and CaO addition ratios on the ethanol steam reforming and CO2 conversion processes to optimize catalyst performance. The experimental results showed that Fe/SiC catalysts effectively promoted the conversion of ethanol and generated high-purity hydrogen, exhibiting excellent catalytic activity. Specifically, a catalyst with 10 % Fe loading and mixed with 0.3g CaO significantly increased the hydrogen yield to 64.4 mmol/g, which was 2.88 times higher than that without the catalyst.

Carbon dioxide electrochemical reduction by copper nanoparticles/ionic liquid-based catalytic inks

The development of copper nanoparticle (CuNP)-based catalysts for the electrochemical reduction of carbon dioxide (ECO2-R) offers a promising approach to enhance its transformation into other industrially significant compounds. This study reports ECO2-R at −1.3 V vs RHE using CuNPs and catalytic inks composed of CuNPs and ionic liquids (ILs), observing significant differences in the selectivity of each catalyst. Specifically, CuNPs alone show a preference for producing ethylene and aqueous products, such as formic acid, ethanol, and formaldehyde. In contrast, the addition of ILs to the catalytic system redirects selectivity toward gaseous products, with methane being the main product. These findings highlight the potential to optimize catalyst composition to tailor the selectivity of CO2 conversion processes. ILs modify the catalytic environment and influence reaction pathways, enabling the selection of specific products.

Inhibiting salt precipitation on the gas diffusion electrode surface in gas-phase CO2 electroreduction to formate by using an acidic anolyte

The gas-phase CO2 electroreduction to formate represents one of the most promising CO2 conversion processes due to its scalability, as the product concentration surpasses 30 % wt. However, the use of alkaline media anolytes, intended to improve the efficiency and selectivity of formate production, causes the carbonate and bicarbonate salts to precipitate over the Gas Diffusion Electrode (GDE). This precipitation clogs the porous structure, leading to a rapid loss of electrode stability. In this work, we address this issue by proposing the use of acid anolytes, based on K2SO4, to mitigate the precipitation of insoluble salt on the GDE structure, thereby achieving longer and more stable GDE operation times. Various anolyte concentrations and pHs are evaluated, with 0.3 M K2SO4 at pH 1, adjusted using H2SO4, providing the best compromise. This condition inhibited potassium carbonate and bicarbonate precipitation, as observed through XRD, SEM, and EDS analysis, while maintaining high CO2 electroreduction to formate performance, with a concentration of 69 g L−1, and a Faradaic Efficiency of 33 %. Furthermore, the anolyte flowrate per geometric area is optimized to maximize the system performance. At a flowrate of 0.85 mL min−1 cm−2, enhanced concentration of 88 g L−1 and a Faradaic Efficiency of 42 % are reached. Besides, long-term experiments demonstrated that GDEs used with alkaline conditions exhibit a larger deactivation constant (0.7652) compared to the GDEs used with acid anolytes (0.3891). This indicates that salt precipitation more rapidly reduces GDE performance under alkaline conditions. These results represent a promising advance in obtaining longer-lasting GDEs, which are crucial to successfully scaling up the CO2 electroreduction to formate.

Solid Oxide Cell Reactor Model for Transient and Stationary Electrochemical H2O and CO2 Conversion Process Studies

The ability of high-temperature solid oxide cell (SOC) electrochemical reactors to efficiently convert atmospheric carbon to high value chemicals for industrial and energy storage applications via CO2 and co-electrolysis makes them a key technology for active carbon utilisation. However, due to additional operational risks from thermochemical reactions on thermal management, limited experimental capacity, and relative novelty, CO2 and co-electrolysis lag behind steam electrolysis in large-scale adoption. Here, a 1D+1D SOC model based on fundamental first principles considering three-dimensional heat transfer was improved via a unique method for representing co-electrolysis electrochemistry, solving with low computational effort. Validation against experimental data for two compositions and pressures, showed high levels of accuracy with respect to characteristic cell voltages, temperatures, and outlet compositions. The model also showed CO2 reduction during co-electrolysis mainly occurred via reverse water gas shift, while CO2 electrolysis still accounted for up to 35% of the total share. Pressurised co-electrolysis operation promotes exothermic methanation, causing pronounced heating of the reactor, consequently reducing the isothermal current density. Therefore, low to moderate pressurisation is likely most suited for coupling with downstream synthesis processes to avoid the installation of unnecessarily large systems and associated high costs.

Strategic design and facile synthesis of porous hyper-cross-linked phosphonium bromide microspheres for catalyzing CO2 conversion to cyclic carbonates

Heterogeneous ionic liquid (IL) catalysts with multiple active sites can be considered as the highly efficient catalyst for CO2 conversion to cyclic carbonates. It is extremely challenging to achieve the strategic design and precise control of multi-site polymeric ILs’ morphology and properties. In this work, we developed a novel and facile polymerization-ionization method employing flexible brominated monomers as raw materials (e.g. 4‑bromo-1-butene) to successfully synthesize porous hyper-cross-linked phosphonium bromide-microspheres (PBr-microspheres), in order to break through the drawbacks of multi-step preparation and difficulty in microsphere forming. Compared with conventional bromine spheres of the same size, the specific surface area of the new synthetic bromine sphere is 16 times, and the average pore size is one-eighth, with 3-times CO2 adsorption capacity, with rich microporous structure and exposed active sites, excellent CO2 adsorption capacity and thermal stability. PBr-microspheres can achieve synergistic effect of physical adsorption and chemical interaction for CO2, thus enhancing the catalytic performance in CO2 conversion process, affording propylene oxide conversion of 99.7 % and propylene carbonate selectivity of 99.9 %, while the catalytic activity did not decrease significantly after reusing 8 runs. This facile controllable synthesis of PBr-microspheres with excellent catalytic performance provides a new idea for heterogeneous ILs-catalyzed CO2 utilization.

High-efficient acetylene synthesis by selective electrochemical formation of CO2-derived CaC2

Acetylene can be used as feedstock for various chemical products, but its raw material has been a fossil fuel, which poses an environmental challenge. One way to address the challenge is to form CaC2 from CO2, which reacts with water to form acetylene. This study demonstrated the selective formation of CaC2 from CO2 by an electrochemical process in NaCl-KCl-CaCl2-CaO melt at 823 K to produce C2H2 with high current efficiency. The CaC2 was formed through two reactions: the carbon electrodeposition from CO2-derived CO32− (Step 1) and the electrochemical reduction of Ca(II) ion on the carbon (Step 2). These two reactions could be controlled by conducting potentiostatic electrolysis under CO2 and Ar atmospheres, resulting in acetylene synthesis with a maximum current efficiency of 92 %. Each electrochemical reaction agreed with the thermodynamic electrode potential. The electrolysis on carbon electrodes revealed that the higher the crystallinity of carbon, the more selectively CaC2 was formed. The CaC2 formation was induced by the reduction of Ca(II) ions on the basal plane of the graphite layer rather than the edge plane. The unique interfacial phenomenon between high-temperature melt and a carbon electrode surface will contribute to realizing a highly efficient CO2 conversion process to acetylene.

Advancing CO2 hydrogenation to formic Acid: DFT insights into Frustrated Lewis Pair−Functionalized UiO−67 catalysts

In this study, we explore the potential of metal–organic frameworks (MOFs) as catalysts for converting CO2 into valuable chemicals. The focus is on integrating frustrated Lewis pairs (FLPs) within the UiO−67 framework. We investigated 12 distinct functionalized FLP moieties (X = −BF2, −BCl2, −BBr2, −BH2, −B(CH3)2, −B(CF3)2, −B(CN)2, −B(NO2)2, −B(OH)2, −B(NH2)2, −B(OCH3)2, and −B(N(CH3)2)2 to determine their ability to activate small molecules within heterogeneous catalysis using density functional theory (DFT). This study reveals two critical stages in the CO2 conversion process with H2 in UiO−67−X. First, the initial heterolytic cleavage of H2 at the FLP site, and second, the subsequent hydrogenation of CO2. The latter involves the addition of a hydride and a proton. Our findings demonstrate that these modifications facilitate efficient dissociation of H2 into Hδ− and Hδ+ with energy barriers ranging from 0.12 to 0.87 eV and CO2 hydrogenation barriers spanning from 0.61 to 1.90 eV. Notably, the −B(CH3)2 functional group exhibited superior effectiveness in CO2 hydrogenation to formic acid (HCOOH; FA). This enhanced activity correlates directly with FLP acidity and the Gibbs free energy changes in H2 dissociation reaction. It highlights the significant influence of FLP−assisted heterolytic dissociation of H2 in the CO2 conversion process. The results of this study do more than introduce metal-free heterogeneous FLPs within MOFs. They also establish a clear link between the functional group composition, FLP acidity, and catalytic efficiency. These insights offer a valuable theoretical foundation for the design of advanced UiO−67−X catalysts. They open up possibilities for transforming greenhouse gases into valuable chemical products, contributing to sustainable chemical synthesis.

A step closer to sustainable CO2 conversion: Limonene carbonate production driven by ionic liquids

This work aims to advance the biocarbonate concept by developing the first process to produce limonene carbonate based on ionic liquids (ILs). Conventional petroleum-derived cyclic carbonates are recognized products partially composed of CO2 with the main drawback of the high energy consumption that imposes epoxide production. In contrast, natural epoxidable compounds, such as terpenes, stand out in the literature as a more sustainable open research line to enable CO2 conversion processes with better sustainable indicators. Limonene, an abundant natural compound, is identified as a key terpene in the aforementioned discussion. Ammonium-based ILs are experimentally selected and optimized, after covering massive anion and cation substituent tuning, achieving high selectivity and competitive yields to limonene carbonate. The reaction-extraction platform concept, which recovers the catalyst by liquid-liquid extraction, is envisioned and developed using a rational experimental-computational approach. The work concludes with a novel process to effectively produce limonene carbonate by using an IL catalyst and water as an extracting solvent. Ultimately, taking advance of the process simulation, a CO2 emissions assessment was conducted. Using renewable raw materials enhances the sustainability of CO2 conversion to cyclic carbonate, reducing global warming impact compared to fossil-based epoxides. However, limonene extraction and epoxidation have a tangible impact on the overall result of CO2 balance, turning efforts outside battery limits of the CO2 conversion process in the search of a limonene carbonate production line with negative neat CO2 emissions that may change the paradigm in the fixation of CO2 through cycloaddition reactions.

Addition of Imidazolium-Based Ionic Liquid to Improve Methanol Production in Polyamine-Assisted CO2 Capture and Conversion Systems Using Pincer Catalysts.

Ionic liquids have been studied as CO2 capture agents. However, they are rarely used in combined CO2 capture and conversion processes. Utilizing imidazolium-based ionic liquids, the conversion of CO2 to methanol was greatly improved in polyamine assisted systems catalyzed by homogeneous pincer catalysts with Ru and Mn metal centers. Among the ionic liquids tested, [BMIM]OAc was found to perform the best under the given reaction conditions. Among the polyamine tested, pentaethylenehexamine (PEHA) led to the highest conversion rates. Ru-Macho and Ru-Macho-BH were the most active catalysts. Direct air capture utilizing PEHA as the capture material was also demonstrated and produced an 86 % conversion of the captured CO2 to methanol in the presence of [BMIM]OAc.

CO2-Based Stable Porous Metal-Organic Frameworks for CO2 Utilization.

The transformation of carbon dioxide (CO2) into functional materials has garnered considerable worldwide interest. Metal-organic frameworks (MOFs), as a distinctive class of materials, have made great contributions to CO2 capture and conversion. However, facile conversion of CO2 to stable porous MOFs for CO2 utilization remains unexplored. Herein, we present a facile methodology of using CO2 to synthesize stable zirconium-based MOFs. Two zirconium-based MOFs CO2-Zr-DEP and CO2-Zr-DEDP with face-centered cubic topology were obtained via a sequential desilylation-carboxylation-coordination reaction. The MOFs exhibit excellent crystallinity, as verified through powder X-ray diffraction and high-resolution transmission electron microscopy analyses. They also have notable porosity with high surface area (SBET up to 3688 m2 g-1) and good CO2 adsorption capacity (up to 12.5 wt %). The resulting MOFs have abundant alkyne functional moieties, confirmed through 13C cross-polarization/magic angle spinning nuclear magnetic resonance and Fourier transform infrared spectra. Leveraging the catalytic prowess of Ag(I) in diverse CO2-involved reactions, we incorporated Ag(I) into zirconium-based MOFs, capitalizing on their interactions with carbon-carbon π-bonds of alkynes, thereby forming a heterogeneous catalyst. This catalyst demonstrates outstanding efficiency in catalyzing the conversion of CO2 and propargylic alcohols into cyclic carbonates, achieving >99% yield at room temperature and atmospheric pressure conditions. Thus, this work provides a dual CO2 utilization strategy, encompassing the synthesis of CO2-based MOFs (20-24 wt % from CO2) and their subsequent application in CO2 capture and conversion processes. This approach significantly enhances overall CO2 utilization.