Recent Advances Hydrogenation of Carbon Dioxide to Light Olefins over Iron-Based Catalysts via the Fischer-Tropsch Synthesis

The massive burning of fossil fuels has been important for economic and social development, but the increase in the CO2 concentration has seriously affected environmental sustainability. In industrial and agricultural production, light olefins are one of the most important feedstocks. Therefore, the preparation of light olefins by CO2 hydrogenation has been intensively studied, especially for the development of efficient catalysts and for the application in industrial production. Fe-based catalysts are widely used in Fischer-Tropsch synthesis due to their high stability and activity, and they also exhibit excellent catalytic CO2 hydrogenation to light olefins. This paper systematically summarizes and analyzes the reaction mechanism of Fe-based catalysts, alkali and transition metal modifications, interactions between active sites and carriers, the synthesis process, and the effect of the byproduct H2O on catalyst performance. Meanwhile, the challenges to the development of CO2 hydrogenation for light olefin synthesis are presented, and future development opportunities are envisioned.

Synergistic effect of K and Zn on Fe-based catalysts for efficient CO2 hydrogenation

Excessive emission of CO2 into the atmosphere has severely impacted the global ecological environment. Converting CO2 into valuable chemicals and fuels is of great significance for sustainable development. However, low activity and undesirable selectivity often result from the inherent inertness of CO2. Herein, K- or/and Zn-modified Fe-based catalysts were prepared by an incipient-wetness impregnation method for CO2 hydrogenation via a cascade reaction. The results indicate that K species exist as K2O while Zn species exist as ZnFe2O4. In the CO2 hydrogenation pathway, K2O facilitates the adsorption of CO2 and restrains the adsorption of H2, accelerating the transformation of CO2 into C2-C4 olefins rather than paraffins while Zn species promote the dispersion of Fe species, leading to improved activity. Synergistically, a K- and Zn-modified Fe-based catalyst (2Zn-10K-Fe/Al) shows excellent catalytic CO2 hydrogenation activity, achieving a CO2 conversion of 77% which is 1.8 times that (42%) of the unmodified Fe-based catalyst (Fe/Al). Our catalyst also shows a significantly promoted selectivity to C2-C4 olefins of 17% in comparison with the Fe/Al catalyst (0%). It is envisioned that such a binary effect of elements might contribute to the low-cost and industrial production of Fe-based catalysts for selective CO2 conversion.

High-yield production of liquid fuels in CO2 hydrogenation on a zeolite-free Fe-based catalyst

Catalytic conversion of CO₂ to long-chain hydrocarbons with high activity and selectivity is appealing but hugely challenging. For conventional bifunctional catalysts with zeolite, poor coordination among catalytic activity, CO selectivity and target product selectivity often limit the long-chain hydrocarbon yield. Herein, we constructed a singly cobalt-modified iron-based catalyst achieving 57.8% C₅₊ selectivity at a CO₂ conversion of 50.2%. The C₅₊ yield reaches 26.7%, which is a record-breaking value. Co promotes the reduction and strengthens the interaction between raw CO₂ molecules and iron species. In addition to the carbide mechanism path, the existence of Co₃Fe₇ sites can also provide sufficient O-containing intermediate species (CO*, HCOO*, CO₃ ²*, and ) for subsequent chain propagation reaction via the oxygenate mechanism path. Reinforced cascade reactions between the reverse water gas shift (RWGS) reaction and chain propagation are achieved. The improved catalytic performance indicates that the KZFe-5.0Co catalyst could be an ideal candidate for industrial CO₂ hydrogenation catalysts in the future.

A Review on Green Hydrogen Valorization by Heterogeneous Catalytic Hydrogenation of Captured CO2 into Value-Added Products

The catalytic hydrogenation of captured CO2 by different industrial processes allows obtaining liquid biofuels and some chemical products that not only present the interest of being obtained from a very low-cost raw material (CO2) that indeed constitutes an environmental pollution problem but also constitute an energy vector, which can facilitate the storage and transport of very diverse renewable energies. Thus, the combined use of green H2 and captured CO2 to obtain chemical products and biofuels has become attractive for different processes such as power-to-liquids (P2L) and power-to-gas (P2G), which use any renewable power to convert carbon dioxide and water into value-added, synthetic renewable E-fuels and renewable platform molecules, also contributing in an important way to CO2 mitigation. In this regard, there has been an extraordinary increase in the study of supported metal catalysts capable of converting CO2 into synthetic natural gas, according to the Sabatier reaction, or in dimethyl ether, as in power-to-gas processes, as well as in liquid hydrocarbons by the Fischer-Tropsch process, and especially in producing methanol by P2L processes. As a result, the current review aims to provide an overall picture of the most recent research, focusing on the last five years, when research in this field has increased dramatically.

Modified fischer-tropsch synthesis: A review of highly selective catalysts for yielding olefins and higher hydrocarbons

Global warming, fossil fuel depletion, climate change, as well as a sudden increase in fuel price have motivated scientists to search for methods of storage and reduction of greenhouse gases, especially CO2. Therefore, the conversion of CO2 by hydrogenation into higher hydrocarbons through the modified Fischer–Tropsch Synthesis (FTS) has become an important topic of current research and will be discussed in this review. In this process, CO2 is converted into carbon monoxide by the reverse water-gas-shift reaction, which subsequently follows the regular FTS pathway for hydrocarbon formation. Generally, the nature of the catalyst is the main factor significantly influencing product selectivity and activity. Thus, a detailed discussion will focus on recent developments in Fe-based, Co-based, and bimetallic catalysts in this review. Moreover, the effects of adding promoters such as K, Na, or Mn on the performance of catalysts concerning the selectivity of olefins and higher hydrocarbons are assessed.

Hydrogenation of Carbon Dioxide to Value-Added Liquid Fuels and Aromatics over Fe-Based Catalysts Based on the Fischer–Tropsch Synthesis Route

Hydrogenation of CO2 to value-added chemicals and fuels not only effectively alleviates climate change but also reduces over-dependence on fossil fuels. Therefore, much attention has been paid to the chemical conversion of CO2 to value-added products, such as liquid fuels and aromatics. Recently, efficient catalysts have been developed to face the challenge of the chemical inertness of CO2 and the difficulty of C–C coupling. Considering the lack of a detailed summary on hydrogenation of CO2 to liquid fuels and aromatics via the Fischer–Tropsch synthesis (FTS) route, we conducted a comprehensive and systematic review of the research progress on the development of efficient catalysts for hydrogenation of CO2 to liquid fuels and aromatics. In this work, we summarized the factors influencing the catalytic activity and stability of various catalysts, the strategies for optimizing catalytic performance and product distribution, the effects of reaction conditions on catalytic performance, and possible reaction mechanisms for CO2 hydrogenation via the FTS route. Furthermore, we also provided an overview of the challenges and opportunities for future research associated with hydrogenation of CO2 to liquid fuels and aromatics.

High C2-C4 selectivity in CO2 hydrogenation by particle size control of Co-Fe alloy nanoparticles wrapped on N-doped graphitic carbon

A catalyst based on first-row Fe and Co with a record of 51% selectivity to C₂-C₄ hydrocarbons at 36% CO₂ conversion is disclosed. The factors responsible for the C₂₊ selectivity are a narrow Co-Fe particle size distribution of about 10 nm and embedment in N-doped graphitic matrix. These hydrogenation catalysts convert CO₂ into C₂-C₄ hydrocarbons, including ethane, propane, n-butane, ethylene and propylene together with methane, CO. Selectivity varies depending on the catalyst, CO₂ conversion, and the operation conditions. Operating with an H₂/CO₂ ratio of 4 at 300°C and pressure on 5 bar, a remarkable combined 30% of ethylene and propylene at 34% CO₂ conversion was achieved. The present results open the way to develop an economically attractive process for CO₂ reduction leading to products of higher added value and longer life cycles with a substantial selectivity.

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Co-Fe nanoparticles wrapped on N-doped graphitic carbon catalyzes CO₂ hydrogenation

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Co-Fe@(N)Carbon affords 51% selectivity to C₂-C₄ hydrocarbons at 36% CO₂ conversion

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At H₂/CO₂ 4, 300°C and 5 bar, a combined 30% of CH₂ = CH₂ and MeCH = CH₂ is achieved

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Particle size (10 nm) and N-doping are crucial to achieve high C₂₊ selectivity

Catalytic Hydrogenation of CO2 to Methanol: A Review

High-efficiency utilization of CO2 facilitates the reduction of CO2 concentration in the global atmosphere and hence the alleviation of the greenhouse effect. The catalytic hydrogenation of CO2 to produce value-added chemicals exhibits attractive prospects by potentially building energy recycling loops. Particularly, methanol is one of the practically important objective products, and the catalytic hydrogenation of CO2 to synthesize methanol has been extensively studied. In this review, we focus on some basic concepts on CO2 activation, the recent research advances in the catalytic hydrogenation of CO2 to methanol, the development of high-performance catalysts, and microscopic insight into the reaction mechanisms. Finally, some thinking on the present research and possible future trend is presented.

Dependence of copper particle size and interface on methanol and CO formation in CO2 hydrogenation over Cu@ZnO catalysts

The copper particle size and the interface of Cu and ZnO showed strong impacts on the formation of methanol and CO in CO2 hydrogenation over Cu@ZnO catalysts.

Direct conversion of CO2 to a jet fuel over CoFe alloy catalysts

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

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The selectivity of the hydrocarbons (63.5%) exceeds the theoretical maximum value

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The CoFe alloy is the active phase in the coupling reaction between surface carbons

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The CoFe alloy is a highly efficient catalyst in the presence of a sodium promoter

Catalysts for the Conversion of CO2 to Low Molecular Weight Olefins-A Review

There is a large worldwide demand for light olefins (C₂⁼-C₄⁼), which are needed for the production of high value-added chemicals and plastics. Light olefins can be produced by petroleum processing, direct/indirect conversion of synthesis gas (CO + H₂) and hydrogenation of CO₂. Among these methods, catalytic hydrogenation of CO₂ is the most recently studied because it could contribute to alleviating CO₂ emissions into the atmosphere. However, due to thermodynamic reasons, the design of catalysts for the selective production of light olefins from CO₂ presents different challenges. In this regard, the recent progress in the synthesis of nanomaterials with well-controlled morphologies and active phase dispersion has opened new perspectives for the production of light olefins. In this review, recent advances in catalyst design are presented, with emphasis on catalysts operating through the modified Fischer-Tropsch pathway. The advantages and disadvantages of olefin production from CO₂ via CO or methanol-mediated reaction routes were analyzed, as well as the prospects for the design of a single catalyst for direct olefin production. Conclusions were drawn on the prospect of a new catalyst design for the production of light olefins from CO₂.

Mechanistic and multiscale aspects of thermo-catalytic CO2 conversion to C1 products

The increasing environmental concerns due to anthropogenic CO2 emissions have called for an alternate sustainable source to fulfill rising chemical and energy demands and reduce environmental problems. The thermo-catalytic activation and conversion of abundantly available CO2, a thermodynamically stable and kinetically inert molecule, can significantly pave the way to sustainably produce chemicals and fuels and mitigate the additional CO2 load. This can be done through comprehensive knowledge and understanding of catalyst behavior, reaction kinetics, and reactor design. This review aims to catalog and summarize the advances in the experimental and theoretical approaches for CO2 activation and conversion to C1 products via heterogeneous catalytic routes. To this aim, we analyze the current literature works describing experimental analyses (e.g., catalyst characterization and kinetics measurement) as well as computational studies (e.g., microkinetic modeling and first-principles calculations). The catalytic reactions of CO2 activation and conversion reviewed in detail are: (i) reverse water-gas shift (RWGS), (ii) CO2 methanation, (iii) CO2 hydrogenation to methanol, and (iv) dry reforming of methane (DRM). This review is divided into six sections. The first section provides an overview of the energy and environmental problems of our society, in which promising strategies and possible pathways to utilize anthropogenic CO2 are highlighted. In the second section, the discussion follows with the description of materials and mechanisms of the available thermo-catalytic processes for CO2 utilization. In the third section, the process of catalyst deactivation by coking is presented, and possible solutions to the problem are recommended based on experimental and theoretical literature works. In the fourth section, kinetic models are reviewed. In the fifth section, reaction technologies associated with the conversion of CO2 are described, and, finally, in the sixth section, concluding remarks and future directions are provided.

Enhancing CO2 Conversion to CO over Plasma-Deposited Composites Based on Mixed Co and Fe Oxides

The hydrogenation of CO2 to produce CO and H2O, known as reverse-water-gas shift reaction (RWGS) is considered to be an important CO2 valorization pathway. This work is aimed at proposing the thin-film catalysts based on iron and cobalt oxides for this purpose. A series of Fe–Co nanocomposites were prepared by the plasma-enhanced chemical vapor deposition (PECVD) from organic cobalt and iron precursors on a wire-mesh support. The catalysts were characterized by SEM/EDX, XPS, XRD, and Raman spectroscopy and studied for hydrogenation of CO2 in a tubular reactor operating in the temperature range of 250–400 °C and atmospheric pressure. The Co-based catalyst, containing crystalline CoO phase, exhibited high activity toward CH4, while the Fe-based catalyst, containing crystalline Fe2O3/Fe3O4 phases, was less active and converted CO2 mainly into CO. Regarding the Fe–Co nanocomposites (incl. Fe2O3/Fe3O4 and CoO), even a small fraction of iron dramatically inhibited the production of methane. With increasing the atomic fraction of iron in the Fe–Co systems, the efficiency of the RWGS reaction at 400 °C increased up to 95% selectivity to CO and 30% conversion of CO2, which significantly exceeded the conversion for pure iron–based films (approx. 9%). The superior performance of the Fe–Co nanocomposites compared to “pure” Co and Fe–based films was proposed to be explained by assuming changes in the electronic structure of the catalyst resulting from the formation of p–n junctions between nanoparticles of cobalt and iron oxides.

Optimizing Active Sites for High CO Selectivity during CO2 Hydrogenation over Supported Nickel Catalysts

Controlling the selectivity of CO₂ hydrogenation catalysts is a fundamental challenge. In this study, the selectivity of supported Ni catalysts prepared by the traditional impregnation method was found to change after a first CO₂ hydrogenation reaction cycle from 100 to 800 °C. The usually high CH₄ formation was suppressed leading to full selectivity toward CO. This behavior was also observed after the catalyst was treated under methane or propane atmospheres at elevated temperatures. In situ spectroscopic studies revealed that the accumulation of carbon species on the catalyst surface at high temperatures leads to a nickel carbide-like phase. The catalyst regains its high selectivity to CH₄ production after carbon depletion from the surface of the Ni particles by oxidation. However, the selectivity readily shifts back toward CO formation after exposing the catalysts to a new temperature-programmed CO₂ hydrogenation cycle. The fraction of weakly adsorbed CO species increases on the carbide-like surface when compared to a clean nickel surface, explaining the higher selectivity to CO. This easy protocol of changing the surface of a common Ni catalyst to gain selectivity represents an important step for the commercial use of CO₂ hydrogenation to CO processes toward high-added-value products.

Highly Selective Olefin Production from CO2 Hydrogenation on Iron Catalysts: A Subtle Synergy between Manganese and Sodium Additives

Mn and Na additives have been widely studied to improve the efficiency of CO₂ hydrogenation to valuable olefins on Fe catalysts, but their effects on the catalytic properties and mechanism are still under vigorous debate. This study shows that Fe-based catalysts with moderate Mn and Na contents are highly selective for CO₂ hydrogenation to olefins, together with low selectivities for both CO and CH₄ and much improved space-time olefin yields compared to state-of-the-art catalysts. Combined kinetic assessment and quasi in situ characterizations further unveil that the sole presence of Mn suppresses the activity of Fe catalysts because of the close contact between Fe and Mn, whereas the introduction of Na mediates the Fe-Mn interaction and provides strong basic sites. This subtle synergy between Na and Mn sheds light on the importance of the interplay of multiple additives that could bring an enabling strategy to improve catalytic activity and selectivity.

CO2 hydrogenation to high-value products via heterogeneous catalysis

Recently, carbon dioxide capture and conversion, along with hydrogen from renewable resources, provide an alternative approach to synthesis of useful fuels and chemicals. People are increasingly interested in developing innovative carbon dioxide hydrogenation catalysts, and the pace of progress in this area is accelerating. Accordingly, this perspective presents current state of the art and outlook in synthesis of light olefins, dimethyl ether, liquid fuels, and alcohols through two leading hydrogenation mechanisms: methanol reaction and Fischer-Tropsch based carbon dioxide hydrogenation. The future research directions for developing new heterogeneous catalysts with transformational technologies, including 3D printing and artificial intelligence, are provided.

Carbon dioxide (CO₂) capture and conversion provide an alternative approach to synthesis of useful fuels and chemicals. Here, Ye et al. give a comprehensive perspective on the current state of the art and outlook of CO₂ catalytic hydrogenation to the synthesis of light olefins, dimethyl ether, liquid fuels, and alcohols.