A series of Prussian blue analogs (PBAs) having a range of crystal structures and compositions was investigated as heterogeneous catalysts for the fixation of carbon dioxide (CO2) to glycidol. The morphology of PBAs was modified, as confirmed by structural characterization, by varying the precipitation method. Of the prepared catalysts, the cubic Zn(II)-Co(III) PBA exhibited the highest catalytic activity (turn-over frequency up to 763 h−1), selectivity (up to 94%), and recyclability for the cycloaddition of CO2 to glycidol. In addition, branched polycarbonate polyols having tunable branching degree (0.15–0.61) and linear polycarbonates of relatively high carbonate content (up to 64.2%) were produced via ring-opening (multibranching) copolymerization of CO2 and various epoxides using a highly amorphous Zn(II)-Co(III) double metal cyanide catalyst. Mechanistic pathways have been proposed by combining experimental results with computational studies.

This study introduced a durable oxygen carrier with surface enrichment of lanthanum on Co3O4 for chemical looping combustion. It employed the surface enrichment in order to optimize the usage of rare earth lanthanum with secured stability of oxygen carriers. The formation of LaCoO3 perovskite on the Co3O4 surface imparts strong durability and overcomes deactivation of Co3O4 while maintaining CO2 selectivity due to its enhanced sintering resistance. Lanthanum dopants were optimized at 10 wt%. Co3O4 with 10 wt% of lanthanum had 93.1% and 95.4% average CO2 selectivity and CH4 conversion at 800 °C for 50 cycles, respectively. The surface enrichment provides not only resistance to sintering but also high oxygen storage capacity for long-term cyclic chemical looping combustion.

As a polycrystalline polymer, isotactic polybutene-1 (iPB-1) will form different crystalline structures when it crystallizes under different conditions. In this work, we found a simple method to manipulate the cell structure of iPB-1 foams by controlling the annealing time of crystalline form II at room temperature and employing supercritical CO2 foaming. As the content of crystalline form II increases, the storage modulus (G′) and complex viscosity (|η * |) increase, and the solubility of CO2 in iPB-1 increases. Crystalline form II has a wider foaming temperature window compared to crystalline form I and exhibits a more uniform cell structure at temperatures between 95 °C and 125 °C. The average cell diameters of crystalline form II and I are 33.9 µm and 11.2 µm at 115 °C and 15 MPa CO2, respectively. A small amount of crystalline form I acts as a heterogeneous nucleation agent during the foaming process, resulting in the formation of a “petal-like” cell structure. During the foaming saturation process, the melted portion of iPB-1 with unstable crystalline form II transforms into crystalline form I′ under high-pressure CO2, while the unmelted portion transforms into crystalline form I. As the pressure increases, the cell structure of iPB-1 undergoes a transition from “petal-like” to bimodal cell structure, ultimately achieving a more uniform structure. Moreover, increasing foaming pressure can also change the cell structure of the foamed material from closed-cell to open-cell. The occurrence of bimodal melting peaks in the foamed samples is beneficial for the adhesion of beads during the molding process.

In this work, chromium(III) Salophen complexes bearing tertiary dimethyl or diethyl amino substituents were synthesized and tested as homogeneous co-catalysts associated with n-Bu4NBr for the cycloaddition of CO2 on styrene epoxide under 11 bar of CO2. Full conversion of styrene oxide into styrene carbonate was obtained after 23 h reaction at 50 °C using Salophen-Me2N-Cr. These results emphasized that tertiary amine groups born by the aromatic cycles of Salophen clearly enhanced the co-catalytic activity of the corresponding Cr(III) complex. The direct conversion of styrene into styrene carbonate was then conducted at 80 °C with O2 and CO2 either under a single set of conditions (reactants and catalysts together) or using a two-steps transformation. The latter was based on the prior epoxidation of styrene in the presence of isobutyraldehyde and O2 (3.5 bar) with a delayed addition of the cycloaddition catalysts (n-Bu4NBr and Salophen-Me2N-Cr) and CO2 (11 bar). Using these conditions, the maximum yield of styrene carbonate, obtained after 3 h of epoxidation and 20 h of cycloaddition (with Salophen-Me2N-Cr), was 31 % at 80 °C. This work demonstrates that the key-point to afford a high styrene carbonate global yield with that system was related to the implementation of a two-step protocol, since it allowed to minimize the amounts of undesired by-products.

To achieve carbon capture and utilization, low-energy-consumption CO2 recovery and conversion technologies are required. However, the majority of previous studies on CO2 capture and conversion have been conducted independently. Therefore, we developed a local carbon recycling system that links these two technologies. In this system, CO2 is recovered from combustion exhaust gases by physical adsorption, the recovered CO2 is converted to CH4 by methanation, and the produced CH4 is used as a fuel. During conversion of the recovered CO2 into CH4, the recovered gas can contain a mixture of CO2 and H2; thus, H2 can be supplied during the desorption process to lower the CO2 partial pressure in the CO2 adsorber (hereafter referred to as H2 sweep). In addition, methanation is an exothermic reaction that can supply heat to the CO2 adsorber. In this study, focusing on the energy consumption of the CO2 adsorber, the effect of combining these two approaches with the conventional vacuum temperature swing adsorption process was investigated. Since this system requires the effective use of the methanation reaction heat, a shell-and-tube CO2 adsorber containing zeolite 13X was constructed. By combining these two approaches for an exhaust gas with a CO2 concentration of 9.6%, a CO2 recovery ratio of 90% was achieved with an energy consumption of 0.9 GJ/t-CO2. Moreover, a superior CO2 recovery ratio of 99% was achieved with an energy consumption of 1.4 GJ/t-CO2, thereby constituting a higher CO2 recovery ratio with a lower energy consumption compared with conventional CO2 adsorption systems.

CO2 sequestration is among the most anticipated methods to mitigate the already detrimental concentrations of CO2 in the atmosphere. Among sequestration methods, CO2 injection into oceans is of great significance due to the oceans’ large sequestration capacity. However, there are concerns about the changes in water pH as CO2 is injected into oceans. Previous studies in conditions representative of CCS in the ocean are scarce. In the current study, we experimentally measure the pH and solubility at pressures up to 400 atm, temperatures between 283 and 298 K, and different aqueous solutions in a high-pressure autoclave reactor. The results indicated that increasing pressure increases the solubility of CO2 in aqueous solutions, resulting in lower pH values. In contrast, increasing salinity and temperature lowers the solubility and, as a result, increases the system's pH. Among all the tested aqueous solutions, the synthetic seawater mimicked that of a potential injection point in the South China sea, exhibiting the highest salting-out effect and, therefore, the lowest solubility (i.e., the highest pH). The experimental dataset of this study was fed to a machine learning algorithm, Group modeling data handling(GMDH), to develop an explainable, white-box solubility model. The model could predict the pH as a function of solubility, temperature, pressure, and salinity with an accuracy of 0.87. The pH values from the model were compared to those from previous studies, and a good agreement among the values was found. Lastly, a parameter importance analysis was conducted to shed further light on the model's performance. Pressure and temperature were found to be the most and the least influential factors, respectively. As the implantation of the technology is currently being considered in China, the current study can pave the way to better understand the interactions and mechanisms involved in conditions representative of ocean sequestration before large-scale operations.

CO2 utilization is a key technology for carbon neutrality and is in high demand worldwide; however, many challenges need to be overcome. Composite catalysts consisting of zirconia-based catalysts for CO2 hydrogenation and zeolite-based solid acid catalysts for methanol-to-olefins reaction have been realized one-pass synthesis of olefins from CO2. High selectivity for olefins is essential for utilizing this promising process, and in this work, we precisely tuned the properties of MOR-type zeolites using multiple-step post-synthetic treatments. Miniaturization by milling and recrystallization helped realize the optimization of the zeolite composition related to the acid strength as well as enhance gas diffusion. Defect-healing treatment recently developed by us was applied, and the defects generated in the framework during these processes were successfully removed. Finally, the optimized sample showed high catalytic activity in sequential CO2 hydrogenation to hydrocarbons with the olefin selectivity with an improvement in the olefin/paraffin ratio from 0.69 to 1.4.

Photocatalytic N-formylation of amines with CO2 is a promising strategy to convert CO2 into value-added chemicals sustainably. In this work, a black TiO2-supported Cu photocatalyst is prepared through a solvothermal method for the N-formylation of N-methylaniline with NaBH4 as the reducing agent. Cu nanoparticles and oxygen vacancies are formed on the surface of the photocatalyst after reduction with H2, which decreases the band-gap energy and promotes the separation of photogenerated electrons and holes, thereby improving the photocatalytic activity remarkably. A 100 % conversion is achieved after 9 h radiation, and the yield of N-methylformanilide reaches 81 %. Both the amount of NaBH4 and the pressure of CO2 show important influences on the activity and selectivity of the photocatalytic process, and the carbon and hydrogen in the aldehyde group are from CO2 and NaBH4, respectively. The photocatalyst also shows promising cycling durability.

Biogenic dendritic fibrous Dy2Sn2O7 (Dy2Sn2O7 BDF) were greenly generated in the attendance of Desulfovibrio alaskensis G20 from tin(IV) chloride pentahydrate and Dy(NO3)3·5 H2O as Sn and Dy sources. The anatomical analysis of the specimen verified the generation of Dy2Sn2O7 BDF in the scope of 300 nm. Specimens created with a Desulfovibrio alaskensis G20 was investigated by employing different approaches. The properties of Dy2Sn2O7 BDF as a nanocatalyst were determined by EDS, TGA, TEM, XRD, and SEM. Due to the high ionic internal character, high mechanical and thermal sustainability, and persistent colloidal stability, the system can be deemed as an ideal nanocatalyst by deploying the host-guest method. Carbon dioxide was converted to dimethyl carbonate products. The products were effortlessly separated from the green medium, and Dy2Sn2O7 BDF was reutilized for several runs without a notable drop in catalytic selectivity and activity.

In addition to the climate crisis’s looming dangers, Europe was recently affected by profoundly volatile energy markets, entailing soaring inflation and political uncertainty. Power-to-Liquid processes have the potential to curb global warming by valorizing CO2 to produce synthetic fuels and platform chemicals while simultaneously substituting fossil energy imports. The impact of the CO2 source, i.e., cement production, biogas upgrading and solid biomass combustion, on Power-to-Liquid plants was evaluated by implementing the designed configuration, including CO2 capture, solid-oxide electrolyzer, Fischer-Tropsch synthesis and steam reforming, in IPSEpro, a stationary equation-based process simulation tool. Maximum Power-to-Liquid efficiency of 63.8% and maximum carbon efficiency of 88.6% were obtained by exploiting CO2 emitted by a biogas upgrading unit. Solid-oxide electrolyzers ranging from 23 MWel. (biogas) to 504 MWel. (cement) are required to process CO2 streams from 4.5 to 100 t/h. In addition, the mass and energy balances of the three considered configurations were determined and embedded in a process flow diagram. The presented study aims to facilitate future decisions concerning carbon capture and utilization policy by assessing the CO2 source’s influence on Power-to-Liquid plants’ key performance indicators. Furthermore, the underlying work supports a sustainable realization of Power-to-Liquid plants by offering a framework for exploiting CO2 sources.

Electrochemical carbon dioxide (CO2) reduction has attracted attention for converting CO2 into value-added products at room temperature. Conventional electrochemical CO2 reduction methods require external energy because of the high overpotential of the oxygen evolution reaction (OER). To overcome the limitation of the OER, we propose a gaseous CO2 reduction system that uses an aqueous hydrazine (N2H4) oxidation reaction. In this study, the N2H4-CO2 fuel cell is proposed for the simultaneous generation of electricity with CO2 conversion. During the operation of the aqueous N2H4/gas-feeding CO2 fuel cell, a power density of 20.31 mW/cm2 was obtained and 49.20 % of CO2 was converted to CO at the Ag cathode. We also evaluated the correlation between the flow rate of the anolyte and the hydrophobicity of the Ag cathode in terms of cell performance.

In this study, the performance of a packed bed membrane reactor (PBMR) based on carbon molecular sieve membranes for the one-step CO2 conversion to dimethyl ether (DME) is experimentally compared to that of a conventional packed bed reactor (PBR) using a CuO-ZnO-Al2O3/HZSM-5 bifunctional catalyst. The PBMR outperforms the PBR in most of the experimental conditions. The benefits were greater at lower GHSV (i.e., conditions that approach thermodynamic equilibrium and water formation is more severe), with both XCO2 and YDME improvements of +35–40 % and +16–27 %, respectively. Larger sweep gas-to-feed (SW) ratios increase the extent of water removal (ca. 80 % at SW=5), and thus the performance of the PBMR. Nevertheless, alongside the removal of water, a considerably amount of all products are removed as well, leading to a greater improvement in the CO yield (+122 %) than the DME yield (+66 %). Higher temperatures selectively improve the rWGS reaction, leading to a lower YDME with respect to the PBR at 260 °C, due to the significant loss of methanol. Furthermore, larger transmembrane pressures (∆P) were not beneficial for the performance of the PBMR due to the excess reactant loss (i.e., 98–99 % at ∆P = 3 bar). Finally, the reactor models developed in our previous studies accurately describe the performance of both the PBR and PBMR in the range of tested conditions. This result is of high relevance, since the reactor models could be used for further optimization studies and to simulate conditions which were not explored experimentally.

Climate change and global warming are among of the most important environmental issues and require adequate and immediate global action to preserve the planet for future generations. One of the essential technologies used to reduce CO2 emissions and mitigate the worst effects of climate change is carbon capture technology. Many efforts have been made by scientists, industrial sectors, and policy-makers in looking for new technology to reduce greenhouse gas emissions and achieve net-zero emission goals. Research and development in creating new technology involve complex processes and require a digital system to optimize big data prediction as well as to reduce production time. A mathematical and statistical approach such as machine learning plays an important role in solving research problems, whereby this approach provides fast results in predicting big data and cost-efficient tools. In this study, a systematic review and bibliometric analysis were used to analyze the research trend, particularly on the keywords, number of publications, citations, countries, and authorship. This information is important for future research directions for researchers who venture into this area. In this study, the bibliometric analysis focuses on 2 main categories: co-authorship (countries and organizations) and keywords (author keyword). Based on the research trend, the United States (USA), China, Iran, Canada, and the United Kingdom are the leading countries contributing to this field since they have the highest publications and citations. Furthermore, the most common keywords used in the selected articles ranked according to the highest link strength. The top 6 keyword list includes machine learning, artificial neural network, CO2 capture, CO2 solubility, metal-organic frameworks (MOFs) and carbon capture and storage. The findings from this study can be used to open a wider spectrum for the research communities by providing global research trends, current innovations and current technology on machine learning in carbon capture application, identifying the active research areas or hot topics and future research direction to help fight climate change issue using smart advanced technology.

Thermoplastic polyurethane (TPU) foams have exhibited promising prospect in many industries such as automobile, sportswear and packaging, due to their outstanding mechanical properties. However, the application of TPU foams prepared by microcellular foaming with CO2 as blowing agents is still limited, due to the serious shrinkage after foaming. Herein, in this study microcellular foaming with mixed CO2 and N2 as co-blowing agents was used to control the shrinking behavior of hexamethylene diisocyanate (HDI)-based TPU foams, and further, the effects of shrinkage, expansion ratio, and cell size on the mechanical properties of TPU foams were decoupled. The results show that the stretching degree of the molecular chain and the solubility of co-blowing agents play a vital role in stabilizing TPU foams. Foams with an expansion ratio of up to 16-fold can be prepared with both pure CO2 and co-blowing agents. The shrinkage ratio of TPU foams prepared with co-blowing agents is 6.3 %, while that of foams prepared with pure CO2 is 37.8 %. Moreover, it is also found that the mechanical properties of TPU foams with a smaller shrinkage ratio are much higher than those with a larger initial expansion ratio and a similar final expansion ratio.

The reprocessing of polyurethane elastomers into foams using supercritical CO2 offers an interesting opportunity to increase interest in the recycling of polyurethane materials. The significance of the chemical structure of the starting polymers in supercritical foaming is not entirely understood, so it is important to thoroughly comprehend this process. For that reason, in the present work, the influence of the hard segment content on the foaming process using supercritical CO2 will be explored. To carry out this work, three films with different hard segment contents (23 wt%, 33 wt%, and 43 wt%) were synthesized, characterized, and foamed. After characterization, it was confirmed that no bands in the wavenumber corresponding with isocyanate (2250 cm−1) or thiol (2540 cm−1) appeared after reaction, corroborating that all reagents have reacted completely. In addition, during the chemical characterization, it was also observed a change in the intensity of the peaks related to nonbonded and H-bonded CO (1712 cm−1 and 1640 cm−1 respectively), which is related to an increase in the crystalline phase of the polymer with the increase in hard segment content. On the other side, once the foaming tests were performed, a shift in the temperature foaming window was seen with the increase in the hard segment content. In addition, it was also observed that there was a better compromise between the expansionability and shrinking after 24 h in the case of the polymer HS_43%, as despite the fact that this polymer achieved the lower values of expansion ratio, it was also the polymer with the lower values of shrinking. Finally, it is also remarkable that, in some cases (for example, HS_43% at 65 ºC and 10 and 15 MPa or HS_3% at 50 ºC and 15 MPa), it was possible to obtain foams with average cell sizes lower than 35 µm, which make them susceptible to being employed in insulation applications.

Commercial methanol catalysts based on Cu/ZnO/Al2O3 are less effective applied to direct hydrogenation of CO2 to methanol. The main reason is that the catalyst deactivation increases with the water pressure and temperature, and from stoichiometry, water formation is equal to the CO2 consumption. Here, the focus is on how the process can be designed to reduce this problem. Multi-stage reactor designs with inter-condensation of water and methanol will reduce the water pressure. Several optimal designs are generated with the use of a path optimization method to maximize the methanol production per pass with the use of the least possible reaction volume and hydrogen. Based on a published kinetic model, the optimal volume stage distribution, coolant temperature, and fluid mixing are found. Two configurations of the tail gas treatment are investigated, a once-though and a recycle configuration. A three-stage reactor design with recycling of the tail gas is found to be the better configuration. High CO2-conversion per pass and a low recycle ratio are obtained. Rigorous process simulations of the most promising designs are made to verify that the pressure drop, temperature peaks, and water pressure are good. The maximum water pressure is low. A shell and tube boiling water type reactor design is selected. For a 10 t h− 1 plant, all tubes of all three stages can be located in the same shell.

CO2 injection in coal causes permeability reduction, but also affects the microcrystalline structure. To quantify the different response of microcrystalline structure of anthracite after multi-phase CO2 injection, anthracite samples from the Qinshui basin, the samples were demineralized by HF-HCl before CO2 injection, then subjected dry, demineralized samples to CO2 injection experiments at 4 MPa (gaseous), 6 MPa (subcritical) and 8 MPa (supercritical) pressure, the microcrystalline quantification was obtained using X-ray diffraction and image analysis of HRTEM micrographs, the morphological characteristics of ultramicropore were quantitatively characterized by HRTEM image analysis. With increasing injection pressure, the interplanar spacing (d002) and aromaticity (fa) of the coal gradually increased, while the average number of aromatic layers (Nc) and unit stacking height (Lc) gradually decreased; the variation in the unit lateral size (La) also became more complex. Thus, the coal crystal structure was altered after CO2 treatment and the degree of damage increased with pressure. Further, the average length of coal lattice fringes becomes shorter with the increase of pressure, while the length, width and area of ultra-micropores in subcritical and supercritical SH and ZZ coal increase. In addition, the average curvature of the lattice fringes became larger, and the directional ordering decreased after CO2 intrusion. Thus, CO2 injection led to the transformations of crystal structure, generating intermolecular structural defects, and a reduction in order in the striation direction. This study presents the microcrystalline structure and ultra-micropore response of anthracite due to CO2 injection, which also helps with in-depth understanding of the impact of CO2-ECBM.

The catalytic activity of 3D-printed metal monoliths loaded with iron impregnated ceria-zirconia mixed-oxide support on CO2 conversion to methane was investigated between 300 and 500 °C under 1 bar and 20 bar pressure. The catalyst was characterised using TPR, XRD, SEM-EDX and in-situ DRIFTS. At 400 °C and atmospheric pressure, the catalyst wash-coated monoliths increased the methane yield by 3.5 times and doubled the CO2 conversion compared to the same catalyst dispersed as a powder. Methane selectivity of 95.2% was obtained at 400 °C and 20 bars pressure. This is the highest methane selectivity recorded in the literature for CO2 methanation using an iron catalyst. The catalyst loaded monoliths were stable over a continuous operation of 100 h at 500 °C and 20 bar. Such increased methane selectivity and yield combined with a long duration stability as well as an economic and easier synthesis process vouches for the great potential of catalyst loaded 3D monoliths for industrial application.

Improvement of the CO2 conversion using a 2.45 GHz microwave plasma torch in reverse vortex configuration with cooled effluent channels at atmospheric pressure is reported. This configuration allows for fast gas quenching by efficient gas cooling of the effluent, which leads to conversion and energy efficiency results at 900 mbar that are very similar to the highest conversion and energy efficiency values typically obtained at lower pressures (100–200 mbar). The convective cooling in long cooled channels proved to be effective, particularly in the configuration with multiple channels, where the effective cooling surface was increased by a factor of 2.4. In comparison with the forward vortex the reverse configuration did not improve conversion, it did improve plasma stability, demonstrating that the observed effect can be attributed to the convective gas cooling in the effluent by gas-surface interaction. High specific energy inputs (> 5.5 eV/ molecule) were achieved in experiments where narrow gas inlets were used, resulting in 8 times higher inlet CO2 velocities that stabilised the plasma, allowing conversion values up to 57% at 900 mbar. The plasma stabilisation was most effective at low flow rates, where high gas velocity confined the plasma to the quartz tube centre and allowed coupling higher power to the plasma (high SEI). Additionally, experiments without a vacuum pump at atmospheric pressure were performed, yielding identical results as at 900 mbar, demonstrating that the vacuum pump is not needed to achieve high conversion rates with the use of the reverse vortex configuration with cooled effluent channels.

Different nano-engineered grazynes have been studied as possible membranes to separate methane (CH4) from carbon dioxide (CO2) by density functional theory (DFT) and molecular dynamics (MD) computational simulations. The study tackles the process thermodynamics, kinetics, and dynamical aspects associated to the diffusion rates and selectivities in the context of biogas upgrading while comparing to other materials available in the literature. Small adsorption energy values have been obtained for three semi-permeable grazynes, with low diffusion energy barriers which severely reduce as long as the grazyne pore increases. Selectivities towards CO2 permeation as large as 39 are found at high pressures for [1],[2]{2}-grazyne, closely followed by [1],[2]{(00),2}-grazyne, posing grazynes as excellent membranes for biogas upgrading with clear advantages compared to scrubbing materials in terms of much improved selectivity, continuous workflow and an order of magnitude larger quantity of separated CO2 per material gram. Present computational simulations reveal that grazynes could be able to upgrade biogas beyond 97 % (v/v) in methane, accomplishing standard worldwide government requirements.