The direct conversion of carbon dioxide (CO2) using green hydrogen is a sustainable approach to jet fuel production. However, achieving a high level of performance remains a formidable challenge due ...to the inertness of CO2 and its low activity for subsequent C–C bond formation. In this study, we prepared a Na-modified CoFe alloy catalyst using layered double-hydroxide precursors that directly transforms CO2 to a jet fuel composed of C8–C16 jet-fuel-range hydrocarbons with very high selectivity. At a temperature of 240°C and pressure of 3 MPa, the catalyst achieves an unprecedentedly high C8–C16 selectivity of 63.5% with 10.2% CO2 conversion and a low combined selectivity of less than 22% toward undesired CO and CH4. Spectroscopic and computational studies show that the promotion of the coupling reaction between the carbon species and inhibition of the undesired CO2 methanation occur mainly due to the utilization of the CoFe alloy structure and addition of the Na promoter. This study provides a viable technique for the highly selective synthesis of eco-friendly and carbon-neutral jet fuel from CO2.
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•An alloy is developed for the direct CO2 hydrogenation to jet-fuel-range hydrocarbons•The selectivity of the hydrocarbons (63.5%) exceeds the theoretical maximum value•The CoFe alloy is the active phase in the coupling reaction between surface carbons•The CoFe alloy is a highly efficient catalyst in the presence of a sodium promoter
A series of CuO-Fe2O3-CeO2 catalysts with various CeO2 doping were prepared via the homogeneous precipitation method, characterized and mechanically mixed with HZSM-5. Their feasibility and ...performance for the synthesis of dimethyl ether (DME) via CO2 hydrogenation in a one-step process were evaluated. The formed stable solid solution after the CuO-Fe2O3 catalyst modified with CeO2 promoted the CuO dispersion, reduced the CuO crystallite size, decreased the reduction temperature of highly dispersed CuO, modified the specific surface area of the CuO-Fe2O3-CeO2 catalyst, and improved the catalytic activity of the CuO-Fe2O3-CeO2 catalyst. The addition of CeO2 to CuO-Fe2O3 catalyst increased the amount of Lewis acid sites and Brønsted acid sites, and enhanced the acid intensity of the weak acid sites, which in turn promoted the catalytic performance of CO2 hydrogenation to DME. The optimal introduced amount of Ce in the catalyst was determined to be3.0 wt%. The CO2 conversion and DME selectivity were 20.9%, and 63.1%, respectively, when the CO2 hydrogenation to DME was carried out at 260°C, and 3.0MPa with a gaseous hourly space velocity of 1500mLgcat−1h−1.
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•CuO-Fe2O3 catalyst modified with different amounts of CeO2 were prepared.•Addition of CeO2 led to the formation of a stable Cu-O-Ce solid solution.•CeO2 can modify the amount of acid sites and acid type of CuO-Fe2O3 catalyst.•Cu-Fe-Ce/HZSM-5 catalyst with 3.0wt% CeO2 showed the optimal catalytic activity.
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•Bifunctional catalysts containing ZnZrOx and MOR-type zeolite were prepared.•The catalysts hydrogenate CO2 to lower olefins in a single stage.•The objective was to develop an optimal ...mixing method of the ZnZrOx and zeolites.•Mixing ZnZrOx with the zeolites in close proximity led to the high olefin yield.•This study will expand the field of bifunctional catalysts using MOR-type zeolites.
In recent years, the issue of global warming caused by CO2 emissions has become a critical problem and poses a worldwide challenge. To address this issue, we have developed a bifunctional catalyst that can convert CO2 to lower olefins in a single stage. Our bifunctional catalysts are a combination of two catalysts, a CO2-to-methanol hydrogenation catalyst (Zn-doped ZrO2, named ZnZrOx) and a methanol-to-olefin catalyst (MOR-type zeolite, named MOR104). In this research, we examined the impact of various mixing modes of the two catalysts on product distribution. We tested four different mixing modes using a down-flow fixed bed reactor: (a) ZnZrOx in the upper layer and MOR104 in the lower layer, (b) catalysts were mixed randomly after being pelletized separately, (c) MOR104 in the upper layer and ZnZrOx in the lower layer, and (d) granulated catalyst produced by physically mixing both catalyst powders. Our findings indicated that the best performance was achieved with catalyst (d), where the two catalysts were mixed in close proximity. This proximity resulted in efficient supply of methanol produced on ZnZrOx to MOR104. In other words, the MTO reaction in MOR104 efficiently consumed methanol molecules produced via equilibrium-limited CO2-to-methanol hydrogenation. When ZnZrOx and MOR104 were thoroughly mixed, the conversion of CO2 to methanol shifted towards the product side, resulting in a greater overall utilization of CO2. Furthermore, the bifunctional catalyst we developed was stable for six hours. Since there have been few studies of bifunctional catalysts containing zeolites other than ZSM-5 and SAPO-34, this study opens up new opportunities for bifunctional catalysts specialized for one-pass hydrocarbon synthesis through CO2 hydrogenation.
The reverse water gas shift (RWGS) reaction converts carbon dioxide (CO2) and hydrogen (H2) to syngas, which is used to produce various high-added-value chemicals. This process has attracted great ...interest from researchers as a way of mitigating the potential environmental impacts of this greenhouse gas, with emphasis on global warming. This work aims to model and simulate an industrial catalytic reactor using kinetic data for the RWGS reaction. The simulation was carried out in Aspen Plus® v10. The thermodynamic analysis showed that the appropriate conditions for the reaction are feed molar ratio (H2/CO2) of 0.8:1, 750 °C, and 20 bar. The RWGS process proceeds in a multi-tubular fixed bed reactor with 36.26% CO2 conversion and 96.41% CO selectivity, at residence times in the order of 2.7 s. These results are at near-equilibrium CO2 conversion with higher CO selectivity.
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•A multi-tubular fixed bed reactor was modeled for the RWGS reaction.•A laboratory-scale catalyst kinetic model has been adjusted for commercial use.•CH4 production was reduced at 750 °C, 20 bar, and 0.8 H2/CO2 molar feed ratio.•36.26% CO2 conversion and 96.41% CO selectivity were achieved.
•We model two emission-to-fuel processes which convert CO2 to fuels.•We optimize the heat exchanger networks for the two processes.•We compare the two processes in terms of energy requirement and ...climate impact.•The process based on CO2 electrolysis is more energy efficient.•Both of the processes can reduce CO2 emissions if renewable energies are used.
Emerging emission-to-liquid (eTL) technologies that produce liquid fuels from CO2 are a possible solution for both the global issues of greenhouse gas emissions and fossil fuel depletion. Among those technologies, CO2 hydrogenation and high-temperature CO2 electrolysis are two promising options suitable for large-scale applications. In this study, two CO2-to-methanol conversion processes, i.e., production of methanol by CO2 hydrogenation and production of methanol based on high-temperature CO2 electrolysis, are simulated using Aspen HYSYS. With Aspen Energy Analyzer, heat exchanger networks are optimized and minimal energy requirements are determined for the two different processes. The two processes are compared in terms of energy requirement and climate impact. It is found that the methanol production based on CO2 electrolysis has an energy efficiency of 41%, almost double that of the CO2 hydrogenation process provided that the required hydrogen is sourced from water electrolysis. The hydrogenation process produces more CO2 when fossil fuel energy sources are used, but can result in more negative CO2 emissions with renewable energies. The study reveals that both of the eTL processes can outperform the conventional fossil-fuel-based methanol production process in climate impacts as long as the renewable energy sources are implemented.
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•Zincian malachite is formed at the low pH and hydrotalcite is produced at pH≥8.0.•With increasing pH, the dCu first increases until pH 9.0 and then decreases.•The catalysts via HTlcs ...show smaller dCu and stronger interaction among Cu and ZnO.•The activity is related to dCu and the synergistic interaction among Cu and ZnO.•The Cu–Zn–Al–Zr catalyst via HTlcs prepared at pH 9.0 shows the best performance.
A series of Cu–Zn–Al–Zr precursor materials are prepared by coprecipitation at different pH values (6.0–11.0) and treated under hydrothermal condition. Zincian malachite is formed as the main phase at the low pH of 6.0 and 7.0, and is replaced by hydrotalcite-like phases with increasing the pH. After calcination and reduction of precursors, Cu/ZnO/Al2O3/ZrO2 catalysts are obtained and tested for methanol synthesis from CO2 hydrogenation at the reaction temperature of 463K. With increasing pH, the Cu particle size first increases until pH 9.0 and then decreases. Compared with the sample resulting from well-crystallized zincian malachite (pH 7.0), the catalysts derived from phase-pure hydrotalcite-like precursors (pH≥9.0) exhibit lower BET specific surface area and lower specific Cu surface area. In addition, due to the smaller of Cu particle size and the stronger interaction among Cu and ZnO, the catalytic activity for the Cu/ZnO/Al2O3/ZrO2 catalysts via the hydrotalcite-like precursors is higher than that for the catalysts derived from zincian malachite precursors at low reaction temperature. A maximum CH3OH yield of 0.087ggcat−1h−1 with the CO2 conversion of 10.7% and the CH3OH selectivity of 81.8% at 463K and 5.0MPa is obtained over the Cu/ZnO/Al2O3/ZrO2 catalyst prepared at pH 9.0.
The vast chemical and structural tunability of metal–organic frameworks (MOFs) are beginning to be harnessed as functional supports for catalytic nanoparticles spanning a range of applications. ...However, a lack of straightforward methods for producing nanoparticle‐encapsulated MOFs as efficient heterogeneous catalysts limits their usage. Herein, a mixed‐metal MOF, NiMg‐MOF‐74, is utilized as a template to disperse small Ni nanoclusters throughout the parent MOF. By exploiting the difference in NiO and MgO coordination bond strength, Ni2+ is selectively reduced to form highly dispersed Ni nanoclusters constrained by the parent MOF pore diameter, while Mg2+ remains coordinated in the framework. By varying the ratio of Ni to Mg in the parent MOF, accessible surface area and crystallinity can be tuned upon thermal treatment, influencing CO2 adsorption capacity and hydrogenation selectivity. The resulting Ni nanoclusters prove to be an active catalyst for CO2 methanation and are examined using extended X‐ray absorption fine structure and X‐ray photoelectron spectroscopy. By preserving a segment of the Mg2+‐containing MOF framework, the composite system retains a portion of its CO2 adsorption capacity while continuing to deliver catalytic activity. The approach is thus critical for designing materials that can bridge the gap between carbon capture and CO2 utilization.
The thermal treatment of mixed‐metal metal–organic frameworks (MOFs) is harnessed to bridge the gap between direct air capture and CO2 methanation with one material. Ni2+ is selectively reduced within the MOF to form highly dispersed Ni nanoclusters active for CO2 hydrogenation. Over 70% of the CO2 adsorption capacity is preserved for the best‐performing catalysts, highlighting the dual functionality of the nanoparticle‐MOF structure.
The use of fossil resources has lead to great increase in concentration of carbon dioxide (CO2) in the atmosphere beyond sustainable limits, which causes environmental issues such as greenhouse gas ...effect, climate change and extreme weather events and threats the human life. Thus, several researches have been focused on mitigate this problem. Possible strategies involve implementing technologies of carbon capture storage and utilization. Among them, integrated processes for carbon dioxide capture and its conversion into value-added products have gained attention. Carbon dioxide hydrogenation is among the most developed technologies for its conversion, but requires an external hydrogen (H2) source. Since the conversion of carbon dioxide is highly energy-demanding, assessing its overall process sustainability requires a comprehensive study on the whole system, including its raw material sources (carbon dioxide and hydrogen). Thus, this work proposes a multi-criteria framework to select suitable sources of carbon dioxide and hydrogen to be used in the conversion of carbon dioxide. Potential sources of carbon dioxide (from power plants to ethanol fermentation) and hydrogen (from dedicated production to by-product hydrogen) were evaluated considering environmental, economic, and technical aspects associated with the usage of each source. The Technique of Order Preference Similarity to the Ideal Solution (TOPSIS) is the multi-criteria decision analysis method used to aggregate the criteria and to rank each source individually and further in a pair-wise assessment to identify potential synergic combinations between carbon dioxide and hydrogen sources. Results suggested that using carbon dioxide from natural gas steam reforming, iron and steel industries, ethylene oxide and other high concentration point sources may be the ideal choice for sustainability. The analysis also indicated that hydrogen may be more sustainable if it is a process by-product or is produced by low-cost wind-powered electrolysis. It is important to consider that the analysis is based on several specific data inputs and assumptions, and that a lower score does not mean that the source is not worth investing in.
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•Using environmental, economic and technical indicators for hydrogen and carbon dioxide sources evaluation.•Multi-criteria decision analysis is used to assess the sustainability of individual sources and their combinations.•By-product hydrogen from steam crackers and coke oven gas showed good sustainability performance.•Using by-product hydrogen or wind-electrolysis with on-site/nearby available CO2 could result in a more sustainable process.
Hydrogenation of CO2 to produce formic acid/formate is a significant pathway for future energy storage and utilization. The development of heterogeneous catalysts with high activity and stability for ...this process is still a challenge. In this work, the in-situ N-doped hierarchical porous carbon derived from distiller's grains was used as a support for Pd-based catalysts (Pd/NC) to convert CO2 into valuable chemicals while making high-value use of waste biomass. The optimum catalyst, Pd/NC-800, shown exceptional catalytic performance, achieving a turnover frequency (TOF) of 2060 h−1 at 100℃, 4 MPa in the catalytic CO2 hydrogenation to formate reaction. Comprehensive experimental results and density functional theory calculations indicate that the electronic effect between the pyridine N in the support and the Pd nanoparticles (NPs) can make the Pd surface reach the state of electron enrichment and enhance the metal-support interaction. Moreover, the synthesized material has hierarchical pore structure, which provides abundant Pd anchor location sites and improves mass transfer efficiency. The results not only provide a feasible strategy for the preparation of efficient CO2 hydrogenation catalysts, but also break a new and effective avenue for the resource utilization of distiller's grains.
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•Facile synthesis of N-doped porous carbons from waste distiller's grains.•Pd/NC-800 exhibits outstanding activity with a TOF value of 2060 h−1 at 373 K.•The electronic state of Pd NPs is influenced by pyridine N.•The synthesized biomass carbon contains abundant hierarchical pore structure.
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