Journal of CO2 Utilization最新文献

The influence of the support on catalytic activity and stability of supported 2Cr-Fe bimetallic catalysts for the CO₂-assisted dehydrogenation (DH) of n-octane has been investigated. Four MgO modified supports viz; MgO-CeO₂ (MgCe), MgO-ZrO₂ (MgZr), MgO-CeO₂-ZrO₂ (MgCeZr) and MgO-SiO₂ (MgSi) were synthesized by the sol-gel combustion technique. The supported catalysts were in turn prepared by vacuum impregnation and thereafter tested for the CO_2-assisted DH of n-octane. The catalysts were characterized by inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray diffraction (XRD), N₂-physisorption, Raman spectroscopy, transmission electron microscopy (TEM), electron dispersive x-ray (EDX), temperature programmed desorption of CO₂ (CO₂-TPD), temperature programmed reduction and oxidation (H₂-TPR and CO₂-TPO), electron paramagnetic resonance (EPR) and thermal gravimetric analysis (TGA) techniques. Raman results showed that the CrO_x is stabilized as mono- and/or polynuclear Cr(VI) species over the 2Cr-Fe/MgCe catalyst, which are reduced to lower oxidation state species during the DH reaction. The 2Cr-Fe/MgZr, 2Cr-Fe/MgCeZr and 2Cr-Fe/MgSi catalysts stabilized the CrO_x as polymerized species, forming the more active Cr-O-Fe polymer units on the catalysts’ surface. XRD, TEM and EDX results showed that the ZrO₂-containing supports have smaller particles and stabilized the active metal oxides in a more dispersed amorphous state. The CO₂-TPO of the pre-reduced catalysts and EPR of the used catalysts indicated that the 2Cr-Fe/MgCeZr undergoes significant re-oxidation by CO₂ during the catalytic process. The 2Cr-Fe/MgCe was the least active, while the 2Cr-Fe/MgZr catalyst showed the best performance and stability over three regeneration cycles. Selectivity to C8 products (octenes and aromatics) was found to strongly depend on the surface basicity of the catalysts. Deactivation of the catalysts was found to follow first order kinetics and coke deposition was identified as the major cause.

Reducing atmospheric CO₂ levels to combat global warming is a pressing concern today. Numerous methods have been employed to capture CO₂ from flue gases. One particularly promising approach is the use of carbonic anhydrases (CAs) as biocatalysts for the rapid conversion of CO₂ to H₂CO₃. However, the widespread application of CAs for CO₂ capture has been hampered by their inherent instability under real-world conditions. In this study, we have successfully engineered a chimeric carbonic anhydrase with vastly improved physicochemical properties, particularly with respect to its resilience to high temperatures, alkaline pH, and saline environments. Using computational design, we created various hybrid CAs with enhanced resistance to elevated temperatures. Among them, a chimeric CA known as SPS, generated by domain exchange between SazCA and PmCA, exhibited superior heat stability compared to its parent CAs. SPS showed 10 % higher enzymatic activity and retained 80–13 % of its activity during a period of 3 h to 24 h of incubation at 100℃. SPS's apparent k_cat and K_m values were 4.84 × 10⁸ s⁻¹ and 13.7 mM, respectively. Structural analysis revealed that SPS forms dimers, which contributes to its robustness. Furthermore, we introduced modifications in the form of SPS_1 and SPS_2 variants by incorporating one or two loop sequences from the halotolerant dCAII into SPS. These modifications significantly improved the stability of the CA in alkaline and saline conditions. In particular, SPS showed remarkable efficiency in hydrating CO₂ in seawater. Given these compelling results, we propose that hybrid CAs such as SPS, SPS_1, and SPS_2 hold great promise for facilitating CO₂ hydration in a wide range of applications.

Synopsis

Greenhouse gas sequestration is an immediate need. This study reports an engineered and highly stable carbonic anhydrase for CO₂ sequestration and greenhouse gas reduction.

Aerogels based on natural polymers are of increasing interest in the biomedical field due to their biocompatibility, bioactivity, biodegradability and, in certain cases, extracellular matrix biomimicry. However, sterility has been a critical quality attribute limiting the use of aerogels in biomedicine. This work introduces a new and environmental-friendly technique based on the use of CO₂ called in situ sterilization that enables the manufacturing of sterile aerogel in a one-pot process. Starch aerogel cylinders and alginate aerogel beads enclosed within sterilization pouches were produced using this approach. The study involved the redesign of the flow diagram for aerogel production and the study of the effect of key parameters in the process (additive type and content, agitation, CO₂ flow regime type and duration) on the resulting material. The obtained materials were evaluated regarding their texture (helium pycnometry, N₂ adsorption-desorption analysis, SEM) and their sterility against three standardized bioindicators. Finally, the sterile aerogel materials were put in contact with NIH-3T3 cells assessing their cytocompatibility. Under the optimal operating conditions with 4.5 h of processing time, the aerogels were sterile, cytocompatible and had a porosity of ca. 80 % and a specific surface area of ca. 80 m²/g and 200 m²/g, for starch and alginate aerogels, respectively. Results allowed to identify the feasible operating region as well as the optimum processing values to obtain the typical nanostructure of aerogels, whilst ensuring suitable regulatory sterilization levels for aerogel implantation and cytocompatibility of the sterile material with fibroblastic cells.

Surface functional groups (SFGs) play a key role in adsorption of any target molecule and CO₂ is no exception. In fact, due to its quadrupole nature, different SFGs may attract either the oxygen or the carbon atoms to facilitate improved sorption characteristics in porous materials, hence the proliferation of this approach in the context of carbon capture via solid adsorbents. However, actual processes involve CO₂ capture/removal from a mixed gas stream that may have a non-negligible water content. The presence of humidity significantly hampers the sorption properties of classical physisorbents. To overcome this, the surface of the adsorbent can be modified to include hydrophobic/hydrophilic SFGs making the materials more resilient to moisture. However, the mechanisms behind H₂O-tolerance depend greatly on the characteristics of SFGs themselves. Herein, a multitude of hydrophobic and hydrophilic SFGs (e.g. carbonyls, halogens, hydroxyls, nitro groups, phenyls, various alkyl chains and etc.) for physical CO₂ adsorption are reviewed within the context of their separation performance in a humid environment, highlighting their merits and limitations as well as their impact on cooperative or competitive H₂O – CO₂ adsorption.

This study explores the combined effects of coal fly ash (FA) and CO₂ curing on the flexural strength, compressive strength, and water resistance of magnesium potassium phosphate cement (MKPC). Additionally, the hydration products and microstructure of MKPC and MKPC-FA blends are examined using X-ray diffraction (XRD), thermogravimetric analysis (TGA), mercury injection porosity (MIP), and scanning electron microscopy (SEM). The results demonstrate that carbonation curing effectively improves the mechanical strength and water resistance of MKPC-FA blends by refining the pore structure and reducing porosity. Incorporating fly ash into magnesium phosphate cement leads to a longer setting time and appropriate enhancement in the water resistance of MKPC-FA blends. It should be mentioned that the mechanical strength of MKPC-FA blends declines with increasing fly ash content, and carbonation curing can partially ameliorate these negative effects. Therefore, both incorporating fly ash and storing carbon dioxide have positive effects on the durability and environmental sustainability aspects associated with MKPC preparation.

Dual function materials (DFMs) are key for the integrated capture of CO₂ from waste gas streams and its valorisation to valuable chemicals, such as syngas. To be able to function in commercial applications, DFMs require both high capture capacity and catalytic activity, achieved by optimising the synergistic interactions among the catalytic metals, support and adsorbent components. To obtain increased interaction, the dry milling process can be used as a sustainable, solvent free, green synthesis method. In this work, we report the performance of RuNi bimetallic DFMs supported on CeO₂-Al₂O₃ and promoted with CaO and Na₂O, synthesised by a mild-energy mechanochemical process. The materials show generally comparable, and sometimes superior, capture capacity and increased activity in Reverse Water-Gas Shift (RWGS) reaction for CO production at 650 °C compared to their counterpart prepared by a conventional impregnation method, underlining the potential of the synthesis method for highly functional DFMs. Remarkably, high activity and stability are also maintained when O₂ is present in the capture step, indicating potential for real exhaust-gases capture applications. Also, direct air capture of CO₂ is reported, further underlining the benefits of the dry milling approach for creating versatile DFMs.

This study proposed mixing HNO₃ solution with low-lime calcium silicate cement (CSC) to enhance the CO₂ capture and mechanical properties after CO₂-curing by increasing Ca²⁺ leaching at the initial stage. To clarify the influences of HNO₃ and the reaction mechanisms, various molar concentrations of HNO₃ (0, 0.01, 0.05, 0.1, 0.2, 0.5, and 1.0 M) were homogenized with CSC using a liquid-to-solid ratio (L/S) of 0.4 and CO₂-cured in a pressurized chamber for 24 h. The impact of HNO₃ on the initial reaction kinetics, Ca²⁺ leaching, phase composition after curing, CO₂ fixation capability, and mechanical performance were investigated. The findings revealed that the incorporation of HNO₃ had a pronounced influence on the degree of reaction, CO₂ fixation, and mechanical performance of CSC pastes. Nevertheless, the excessive incorporation of HNO₃ had a notable adverse impact on the reaction.

The majority of conventional flame retardants are made by chemical processes using petroleum resources, which cause serious pollution and waste of resources in the ecological environment. In this paper, flame retardants such as L-aspartic acid, DL-serine, L-tyrosine, L-lysine, L-phenylalanine, L-histidine, L-tryptophan, and glycine were employed to finish poly-(ethylene terephthalate) (PET) fabrics with supercritical CO₂ fluid. Scanning electron microscope (SEM) and Energy dispersive spectroscopy (EDS) were used to examine. the microstructure and chemical composition of flame-retardant PET fabrics. The limiting oxygen index (LOI) test and the vertical combustion test were used to assess the flame-retardant qualities of PET fabrics. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to test and assess the thermal properties of PET fabrics. The strength test was used to assess the mechanical properties of PET fabrics. The results showed that the amino acid flame retardants were successfully finished on the PET fabrics by supercritical CO₂ (SC-CO₂) technology and improved the thermal stability of the PET fabric. In comparison to untreated PET fabric, the elongation at break was 13–15 % greater, and the breaking strength was not reduced. Among them, the PET fabrics treated with L-aspartic acid and L-lysine had better flame-retardant performance, there were no droplets, the LOI values were greater than 30 %, and the char length was less than 10 cm. After 45 minutes of soaping and 3 times of washing, the LOI values were still above 28 %, and there were no droplets. Therefore, the PET fibers treated with amino acids using SC-CO₂ technology effectively improved the flame-retardant performance of PET fabrics.

This study introduces a straightforward synthesis method for producing a hybrid material composed of halloysite and kojic acid, which catalyzes carbon dioxide (CO₂) conversion processes. Kojic acid, derived from malted rice fermentation, exhibits inherent chelating properties that facilitate the introduction of copper ions onto the material’s surface. Copper ions, an economically viable alternative to noble metals, catalyze CO₂ conversion reactions effectively. The hybrid catalyst was evaluated for two distinct CO₂ conversion pathways: photocatalytic methane production under simulated sunlight and CO₂ fixation into cyclic carbonates via epoxide reactions. The hybrid material demonstrates remarkable catalytic activity under mild conditions, achieving high conversion efficiencies at 45 °C for methane production and 70 °C for carbonate fixation at atmospheric pressure. Conversion of 31 % and 89 % were achieved for the photocatalytic CO₂ reduction and the carbonate fixation, respectively. FT-IR spectra confirmed the functionalization of the material. Additionally, its organic/inorganic hybrid nature is complemented by excellent thermal stability, as studied by TGA. It enables repeated utilization, maintaining a 25 % catalytic activity for methane production and 70 % for carbonate fixation after the fourth reuse. This research highlights the potential of using naturally derived materials for sustainable CO₂ mitigation.

Sector coupling plays a crucial role in reducing $C{O}_2$ emissions. The usage of renewable energies in Power-to-Liquid (PtL) processes is one option to link the energy, transport and chemical sectors. In addition to the sectors mentioned, other industries such as the cement industry need to be coupled for decarbonization. The BlueFire research project focuses on the investigation of an innovative process, plasma-based calcium looping. This process has the potential to serve as a fundamental component of a PtL plant by absorbing $C{O}_2$ from the environment and converting it into the syngas component carbon monoxide. It is furthermore an option for electrification of the important process of calcination in the cement industry. In this study, a techno-economic analysis is carried out to evaluate the potential of the plasma-based calcium looping. Integrated in a PtL plant to produce marine diesel, scenarios for the years 2020 and 2050 as well as different process schemes are defined in order to investigate the effects of different optimizations. In 2050, the integration of the plasma-based calcium looping is estimated to increase the PtL efficiency from 25 % to 32 %. This leads to net production costs ($\mathrm{NPC}$) of 2.5 EUR/L marine diesel. By illustrating the techno-economic potential, further development goals can be set to achieve $\mathrm{NPC}$ below 2.0 EUR/L. This can be achieved in the presented process setup with plasma efficiencies of 45 % at conversions of 65 %. The investigations allow statements regarding the system integration and the degree of optimization of the plasma-based calcium looping.