Can we afford to waste carbon dioxide? Carbon dioxide as a valuable source of carbon for the production of light olefins

Zn promoted GaZrOx Ternary Solid Solution Oxide Combined with SAPO-34 Effectively Converts CO2 to Light Olefins with Low CO Selectivity

We proposed a new strategy for CO2 hydrogenation to prepare light olefins by introducing Zn into GaZrOx to construct ZnGaZrOx ternary oxides, which was combined with SAPO-34 to prepare a high-performance ZnGaZrOx/SAPO-34 tandem catalyst for CO2 hydrogenation to light olefins. By optimizing the Zn doping content, the ratio and mode of the two-phase composite, and the process conditions, the 3.5 %ZnGaZrOx/SAPO-34 tandem catalyst showed excellent catalytic performance and good high-temperature inhibition of the reverse water-gas shift (RWGS) reaction. The catalyst achieved 26.6 % CO2 conversion, 82.1 % C2 =-C4 = selectivity and 11.8 % light olefins yield. The ZnGaZrOx formed by introducing an appropriate amount of Zn into GaZrOx significantly enhanced the spillover H2 effect and also induced the generation of abundant oxygen vacancies to effectively promote the activation of CO2. Importantly, the RWGS reaction was also significantly suppressed at high temperatures, with the CO selectivity being only 46.1 % at 390 °C.

Recent Developments in Reversible CO2 Hydrogenation and Formic Acid Dehydrogenation over Molecular Catalysts

Carbon dioxide (CO2), a valuable feedstock, can be reutilized as a hydrogen carrier by hydrogenating CO2 to formic acid (FA) and releasing hydrogen by FA dehydrogenation in a reversible manner. Notably, FA is liquid at room temperature and can be stored and transported considerably more safely than hydrogen gas. Herein, we extensively reviewed transition-metal-based molecular catalysts explored for reversible CO2 hydrogenation and FA dehydrogenation. This Review describes different approaches explored for carbon-neutral hydrogen storage and release by applying CO2 hydrogenation to FA/formate and the subsequent release of H2 by the dehydrogenation of FA over a wide range of molecular catalysts based on noble and non-noble metals. Emphasis is also placed on the specific catalyst-to-substrate interaction by highlighting the specific role of the catalyst in the CO2 hydrogenation-FA dehydrogenation pathway.

Structure Sensitivity of CO2 Hydrogenation on Ni Revisited

Despite the large number of studies on the catalytic hydrogenation of CO2 to CO and hydrocarbons by metal nanoparticles, the nature of the active sites and the reaction mechanism have remained unresolved. This hampers the development of effective catalysts relevant to energy storage. By investigating the structure sensitivity of CO2 hydrogenation on a set of silica-supported Ni nanoparticle catalysts (2-12 nm), we found that the active sites responsible for the conversion of CO2 to CO are different from those for the subsequent hydrogenation of CO to CH4. While the former reaction step is weakly dependent on the nanoparticle size, the latter is strongly structure sensitive with particles below 5 nm losing their methanation activity. Operando X-ray diffraction and X-ray absorption spectroscopy results showed that significant oxidation or restructuring, which could be responsible for the observed differences in CO2 hydrogenation rates, was absent. Instead, the decreased methanation activity and the related higher CO selectivity on small nanoparticles was linked to a lower availability of step edges that are active for CO dissociation. Operando infrared spectroscopy coupled with (isotopic) transient experiments revealed the dynamics of surface species on the Ni surface during CO2 hydrogenation and demonstrated that direct dissociation of CO2 to CO is followed by the conversion of strongly bonded carbonyls to CH4. These findings provide essential insights into the much debated structure sensitivity of CO2 hydrogenation reactions and are key for the knowledge-driven design of highly active and selective catalysts.

Catalysis for e-Chemistry: Need and Gaps for a Future De-Fossilized Chemical Production, with Focus on the Role of Complex (Direct) Syntheses by Electrocatalysis

The prospects, needs and limits in current approaches in catalysis to accelerate the transition to e-chemistry, where this term indicates a fossil fuel-free chemical production, are discussed. It is suggested that e-chemistry is a necessary element of the transformation to meet the targets of net zero emissions by year 2050 and that this conversion from the current petrochemistry is feasible. However, the acceleration of the development of catalytic technologies based on the use of renewable energy sources (indicated as reactive catalysis) is necessary, evidencing that these are part of a system of changes and thus should be assessed from this perspective. However, it is perceived that the current studies in the area are not properly addressing the needs to develop the catalytic technologies required for e-chemistry, presenting a series of relevant aspects and directions in which research should be focused to develop the framework system transformation necessary to implement e-chemistry.

Reuse of CO2 in energy intensive process industries

Closing the carbon cycle and enabling a carbon circular economy in energy intensive industries (iron and steel, cement, refineries, petrochemistry and fertilizers) are topics of increasing interest to meet the demanding target of defossilizing the production. The focus of this perspective contribution is on CO₂ reuse technologies in this context. While this is a topic with abundant literature, the analysis of applying CO₂ reuse technologies evidences the need to go beyond those receiving most of the attention today, such as conversion of CO₂ to methanol. Depending on the specific context, different scenarios are expected. Some examples illustrating the search for novel solutions are provided, such as those starting from the efficient conversion of CO₂ to CO. Once CO is produced from CO₂ many bio-chemical and catalytic conversion routes open up next to direct uses of CO in the steel and chemical sector.

Coupling of propane with CO2 to propylene over Zn-promoted In/HZSM-5 catalyst

The ZnIn/HZSM-5 catalyst was prepared by the wetness impregnation method, and the structure of catalyst was characterized by XRD, SEM, TEM, H2-TPR, NH3-TPD, XPS, TG, and N2 adsorption–desorption and then investigated in the coupling of propane with CO2 to propylene. It is found that the addition of Zn species is beneficial to the dispersion of In2O3 over HZSM-5, which plays an important role in propene formation, and adjusts the acidity distribution of In/HZSM-5 catalyst, as well as significantly improves the activity of In/HZSM-5 catalyst. The selectivity of propylene is 68.21% in the coupling of propane with CO2 over ZnIn/HZSM-5 catalyst when the time on stream (TOS) is 2 h, reaction temperature is 580 °C, reaction pressure is 0.3 MPa, C3H6:CO2:N2 = 1:4:5, catalyst mass is 0.2 g, and space velocity is 6000 mL gcat−1 h−1. However, the selectivity of propylene is only 63.33% and 0.25% in the propane dehydrogenation or CO2 hydrogenation reaction, respectively. The ZnIn/HZSM-5 catalyst showed a higher stability with only 0.80% conversion drop after three cycles.

Carbon Dioxide Hydrogenation to Formate Catalyzed by a Bench-Stable, Non-Pincer-Type Mn(I) Alkylcarbonyl Complex

The catalytic reduction of carbon dioxide is a process of growing interest for the use of this simple and abundant molecule as a renewable building block in C1-chemical synthesis and for hydrogen storage. The well-defined, bench-stable alkylcarbonyl Mn(I) bis(phosphine) complex fac-[Mn(CH₂CH₂CH₃)(dippe)(CO)₃] [dippe = 1,2-bis(diisopropylphosphino)ethane] was tested as an efficient and selective non-precious-metal precatalyst for the hydrogenation of CO₂ to formate under mild conditions (75 bar total pressure, 80 °C), in the presence of a Lewis acid co-catalyst (LiOTf) and a base (DBU). Mechanistic insight into the catalytic reaction is provided by means of density functional theory (DFT) calculations.

Capture and Reuse of Carbon Dioxide (CO2) for a Plastics Circular Economy: A Review

Plastic production has been increasing at enormous rates. Particularly, the socioenvironmental problems resulting from the linear economy model have been widely discussed, especially regarding plastic pieces intended for single use and disposed improperly in the environment. Nonetheless, greenhouse gas emissions caused by inappropriate disposal or recycling and by the many production stages have not been discussed thoroughly. Regarding the manufacturing processes, carbon dioxide is produced mainly through heating of process streams and intrinsic chemical transformations, explaining why first-generation petrochemical industries are among the top five most greenhouse gas (GHG)-polluting businesses. Consequently, the plastics market must pursue full integration with the circular economy approach, promoting the simultaneous recycling of plastic wastes and sequestration and reuse of CO2 through carbon capture and utilization (CCU) strategies, which can be employed for the manufacture of olefins (among other process streams) and reduction of fossil-fuel demands and environmental impacts. Considering the previous remarks, the present manuscript’s purpose is to provide a review regarding CO2 emissions, capture, and utilization in the plastics industry. A detailed bibliometric review of both the scientific and the patent literature available is presented, including the description of key players and critical discussions and suggestions about the main technologies. As shown throughout the text, the number of documents has grown steadily, illustrating the increasing importance of CCU strategies in the field of plastics manufacture.

Cyclic Carbonate Formation from Epoxides and CO2 Catalyzed by Sustainable Alkali Halide-Glycol Complexes: A DFT Study to Elucidate Reaction Mechanism and Catalytic Activity

We provide a comprehensive DFT investigation of the mechanistic details of CO2 fixation into styrene oxide to form styrene carbonate, catalyzed by potassium iodide-tetraethylene glycol complex. A detailed view on the intermediate steps of the overall reaction clarifies the role of hydroxyl substances as co-catalysts for the alkali halide-catalyzed cycloaddition. The increase of iodide nucleophilicity in presence of tetraethylene glycol is examined and rationalized by NBO and Hirshfeld charge analysis, and bond distances. We explore how different alkali metal salts and glycols affect the catalytic performance. Our results provide important hints on the synthesis of cyclic carbonates from CO2 and epoxides promoted by alkali halides and glycol complexes, allowing the development of more efficient catalysts.

Catalytic Conversion of Carbon Dioxide Using Binuclear Double-Stranded Helicates: Cyclic Carbonate from Epoxides and Diol

The construction of sophisticated molecular architectures from chemical subunits requires careful selection of the spacers, precise synthetic strategies, and substantial efforts. Here, we report a series of binuclear double-stranded helicates synthesized from different combinations of pyridyl hydrazone-based multidentate ligands (H₂ 1, H₂ 2, H₂ 3) by increasing the methylene spacer and transition metals (Co, Ni, and Zn). The ligands H₂ 1 (N'1,N'3-bis((E)-pyridin-2-ylmethylene)malonohydrazide), H₂ 2 (N'1,N'4-bis((E)-pyridin-2-ylmethylene)succinohydrazide), and H₂ 3 (N'1,N'5-bis((E)-pyridin-2-ylmethylene)glutarohydrazide) and their respective complexes with Co, Ni, and Zn were obtained. Single-crystal X-ray diffraction studies of these binuclear metallohelicates confirm the double-stranded helical structure of the complexes derived from H₂ 2. The set of helicates Co-1, Co-2, and Co-3; Ni-1, Ni-2, and Ni-3; and Zn-1, Zn-2, and Zn-3 were investigated for its catalytic activity in the cyclic carbonate formation reaction. Intriguingly, among the synthesized catalyst, Co-1 was found to be better in terms of conversions with the calculated TOF (turnover frequency) of 128/h. The catalytic performance was significantly improved by adding 0.2 mmol of tetrabutylammonium bromide by achieving 76% conversion in 30 min, with the observed TOF of 15,934 h^-1/molecule and 7967 h^-1/Co center. The results obtained herein show that the double-stranded helicates are effective catalysts for converting both terminal and non-terminal epoxides into their corresponding cyclic carbonates. The striking feature of this catalytic protocol lies in demonstrating the catalytic activity for the conversion of diol to cyclic carbonate, and the detailed kinetic experiments tempted us to propose a tentative reaction mechanism for this conversion.

A Well-Defined Core-Shell-Structured Capsule Catalyst for Direct Conversion of CO2 into Liquefied Petroleum Gas

A Pd/SiO₂ @S1@H-ZSM-5 capsule catalyst (Pd/SiO₂ -SZ) is fabricated through a dual-layer crystal growth method with an auxiliary hydrothermal reaction. The catalyst exhibits excellent selectivity to liquefied petroleum gas (LPG) in CO₂ hydrogenation reactions, which is attributed to the tandem reactions of methanol synthesis on the Pd/SiO₂ core catalyst and methanol dehydration to hydrocarbons on the H-ZSM-5 shell. The Pd/SiO₂ -SZ capsule catalyst has a similar mesoporous structure, narrow range of Pd particles size distribution, and consistent reduction characteristics to the Pd/SiO₂ core catalyst. It maintains the physical and chemical properties of the core catalyst throughout the H-ZSM-5 shell synthesis process. Energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy results reveal that the H-ZSM-5 zeolite shell completely encapsulates the Pd/SiO₂ core catalyst. Compared with the crushed capsule catalyst (Pd/SiO₂ -SZP), the well-defined-structured Pd/SiO₂ -SZ catalyst has a much higher LPG selectivity of 33.6 %, owing to the well-matched reactions at the Pd/SiO₂ core and H-ZSM-5 shell.

Design and Performance Comparison of Methanol Production Processes with Carbon Dioxide Utilization

Carbon dioxide recycling is one of the possible contributions to CO2 mitigation and provides an opportunity to use a low-cost carbon source. Methanol is a commodity chemical that serves as an important basic chemical and energy feedstock with growing demand. For each of the four types of industrial methanol production processes from natural gas (methane), i.e., steam reforming (SR), autothermal reforming (ATR), combined reforming (CR), and two-step reforming (TSR), CO2 utilization cases of (A) no utilization, (B) as reforming step feedstock, and (C) as methanol synthesis step feedstock were designed based on common industrial operation conditions and analyzed for energy consumption, exergy loss (EXloss), net CO2 reduction (NCR) and internal rate of return (IRR). The utilization of CO2 can reduce energy consumption. The processes with the lowest and the highest EXloss are SR and ATR, respectively. All SR processes give negative NCR. All the B-type processes are positive in NCR except B-SR. The highest NCR is obtained from the B-ATR process with a value of 0.23 kg CO2/kg methanol. All the processes are profitable with positive IRR results and the highest IRR of 41% can be obtained from B-ATR. The utilization of CO2 in the industrial methanol process can realize substantial carbon reduction and is beneficial to process economics.

A Critical Look at Direct Catalytic Hydrogenation of Carbon Dioxide to Olefins

One of the main initiatives for fighting climate change is to use carbon dioxide as a resource instead of waste. In this respect, thermocatalytic carbon dioxide hydrogenation to high-added-value chemicals is a promising process. Among the products of this reaction (alcohols, alkanes, olefins, or aromatics), light olefins are interesting because they are building blocks for making polymers, as well as other important chemicals. Olefins are mainly produced from fossil fuel sources, but the increasing demand of plastics boosts the need to develop more sustainable synthetic routes. This review gives a critical overview of the most recent achievements in direct carbon dioxide hydrogenation to light olefins, which can take place through two competitive routes: the modified Fischer-Tropsch synthesis and methanol-mediated synthesis. Both routes are compared in terms of catalyst development, reaction performance, and reaction mechanisms. Furthermore, practical aspects of the commercialization of this reaction, such as renewable hydrogen production and carbon dioxide capture, compression, and transport, are discussed. It is concluded that, to date, the catalysts used in the carbon dioxide hydrogenation reaction give a wide product distribution, which reduces the specific selectivity to lower olefins. More efforts are needed to reach better control of the C/H surface ratio and interactions within the functionalities of the catalyst, as well as understanding the reaction mechanism and avoiding deactivation. Renewable H₂ production and carbon dioxide capture and transport technologies are being developed, although they are currently still too expensive for industrial application.

Recent In Situ/Operando Spectroscopy Studies of Heterogeneous Catalysis with Reducible Metal Oxides as Supports

For heterogeneous catalysis, the metal catalysts supported on reducible metal oxides, especially CeO2 and TiO2, have long been a research focus because of their excellent catalytic performance in a variety of catalytic reactions. Detailed understanding of the promotion effect of reducible metal oxides on catalytic reactions is beneficial to the rational design of new catalysts. The important catalytic roles of reducible metal oxides are attributed to their intimate interactions with the supported metals (e.g., strong metal-support interaction, electronic metal-support interaction) and unique support structures (e.g., oxygen vacancy, reversible valence change, surface hydroxyl). However, the structures of the catalysts and reaction mechanisms are strongly affected by environmental conditions. For this reason, in situ/operando spectroscopy studies under working conditions are necessary to obtain accurate information about the structure-activity relationship. In this review, the recent applications of the in situ/operando spectroscopy methodology on metal catalysts with reducible metal oxides as supports are summarized.

Kinetic Modeling of Catalytic Olefin Cracking and Methanol-to-Olefins (MTO) over Zeolites: A Review

The increasing demand for lower olefins requires new production routes besides steam cracking and fluid catalytic cracking (FCC). Furthermore, less energy consumption, more flexibility in feed and a higher influence on the product distribution are necessary. In this context, catalytic olefin cracking and methanol-to-olefins (MTO) gain in importance. Here, the undesired higher olefins can be catalytically converted and, for methanol, the possibility of a green synthesis route exists. Kinetic modeling of these processes is a helpful tool in understanding the reactivity and finding optimum operating points; however, it is also challenging because reaction networks for hydrocarbon interconversion are rather complex. This review analyzes different deterministic kinetic models published in the literature since 2000. After a presentation of the underlying chemistry and thermodynamics, the models are compared in terms of catalysts, reaction setups and operating conditions. Furthermore, the modeling methodology is shown; both lumped and microkinetic approaches can be found. Despite ZSM-5 being the most widely used catalyst for these processes, other catalysts such as SAPO-34, SAPO-18 and ZSM-23 are also discussed here. Finally, some general as well as reaction-specific recommendations for future work on modeling of complex reaction networks are given.

Highly Dispersed Metal Carbide on ZIF-Derived Pyridinic-N-Doped Carbon for CO2 Enrichment and Selective Hydrogenation

Catalytic conversion of CO₂ into chemicals is a critical issue for energy and environmental research. Among such reactions, converting CO₂ into CO has been regarded as a significant foundation to generate a liquid fuels and chemicals on a large scale. In this work, zeolitic imidazolate framework-derived N-doped carbon-supported metal carbide catalysts (M/ZIF-8-C; M=Ni, Fe, Co and Cu) with highly dispersed metal carbide were prepared for selective CO₂ hydrogenation. Under the same metal loadings, catalytic activity for CO₂ hydrogenation to CO follows the order: Ni/ZIF-8-C≈Fe/ZIF-8-C>Co/ZIF-8-C>Cu/ZIF-8-C. These catalysts are composed of carbide or metal supported on pyridinic N sites within the N-doped carbon structure. ZIF-8-derived pyridinic nitrogen and carbide effect CO₂ adsorption, whereas dispersed Ni or Fe carbide and metal species serve as an active site for CO₂ hydrogenation. The supported Ni catalyst exhibits extraordinary catalytic performance, which results from high dispersion of the metal and exposure of the carbide. Based on high-sensitivity low-energy ion scattering (HS-LEIS) and line scan results, density functional theory (DFT) was used to understand reaction mechanism of selective CO₂ hydrogenation over Ni/ZIF-8-C. The product CO is derived mainly from the direct cleavage of C-O bonds in CO₂ * rather than decomposition of COOH*. The CO* desorption energy on Ni/ZIF-8-C is lower than that for further hydrogenation and dissociation. Comparison of Ni/ZIF-8-C with ZIF-8-C indicates that the combined effects of the highly dispersed metal or carbide and weak CO adsorption result in high CO selectivity for CO₂ hydrogenation.

Beyond Solar Fuels: Renewable Energy-Driven Chemistry

The future feasibility of decarbonized industrial chemical production based on the substitution of fossil feedstocks (FFs) with renewable energy (RE) sources is discussed. Indeed, the use of FFs as an energy source has the greatest impact on the greenhouse gas emissions of chemical production. This future scenario is indicated as "solar-driven" or "RE-driven" chemistry. Its possible implementation requires to go beyond the concept of solar fuels, in particular to address two key aspects: i) the use of RE-driven processes for the production of base raw materials, such as olefins, methanol, and ammonia, and ii) the development of novel RE-driven routes that simultaneously realize process and energy intensification, particularly in the direction of a significant reduction of the number of the process steps.

Kinetics of CO2 Hydrogenation to Hydrocarbons over Iron-Silica Catalysts

The conversion of CO₂ to hydrocarbons is increasingly seen as a potential alternative source of fuel and chemicals, while at the same time contributing to addressing global warming effects. An understanding of kinetics and mass transfer limitations is vital to both optimise catalyst performance and to scale up the whole process. In this work we report on a systematic investigation of the influence of the different process parameters, including pore size, catalyst support particle diameter, reaction temperature, pressure and reactant flow rate on conversion and selectivity of iron nanoparticle -silica catalysts. The results provided on activation energy and mass transfer limitations represent the basis to fully design a reactor system for the effective catalytic conversion of CO₂ to hydrocarbons.

New insights into the effect of sodium on Fe3O4- based nanocatalysts for CO2 hydrogenation to light olefins

Na-containing Fe₃O₄ nanocatalysts show improved performance in CO₂ hydrogenation due to enhanced surface basicity and carburization induced by residual Na.

A novel zinc based binary catalytic system for CO2utilization under mild conditions

A novel zinc based binary catalytic system for the synthesis of cyclic carbonates under mild and solvent-free conditions utilizing CO₂as a C1 building block is reported.

Recyclable Bifunctional Polystyrene and Silica Gel-Supported Organocatalyst for the Coupling of CO2 with Epoxides

A bifunctional ammonium salt covalently bound to a polystyrene or silica support proved to be an efficient and recyclable catalyst for the solvent-free synthesis of cyclic carbonates from epoxides and CO2 . The catalyst can be easily recovered by simple filtration after the reaction and reused in up to 13 consecutive runs with retention of high activity and selectivity even at 90 °C. The scope and limitations of the reaction has been evaluated in terms of reaction conditions and substrate scope.

Carbon cycle in advanced coal chemical engineering

This review summarizes how the carbon cycle occurs and how to reduce CO2 emissions in highly efficient carbon utilization from the most abundant carbon source, coal. Nowadays, more and more attention has been paid to CO2 emissions and its myriad of sources. Much research has been undertaken on fossil energy and renewable energy and current existing problems, challenges and opportunities in controlling and reducing CO2 emission with technologies of CO2 capture, utilization, and storage. The coal chemical industry is a crucial area in the (CO2 value chain) Carbon Cycle. The realization of clean and effective conversion of coal resources, improving the utilization and efficiency of resources, whilst reducing CO2 emissions is a key area for further development and investigation by the coal chemical industry. Under a weak carbon mitigation policy, the value and price of products from coal conversion are suggested in the carbon cycle.

Plasmon-enhanced reverse water gas shift reaction over oxide supported Au catalysts

Visible light driven plasmon-enhanced reverse water gas shift reaction over Au/TiO₂catalysts for CO₂conversion.

Carbon dioxide hydrogenation to methanol over Cu/ZrO2/CNTs: effect of carbon surface chemistry

The excellent catalytic performance of Cu/ZrO₂/CNTs is related to its H₂ and CO₂ adsorption capability, originating from nitrogen species on CNT.