State of the art and perspectives in catalytic processes for CO2 conversion into chemicals and fuels: The distinctive contribution of chemical catalysis and biotechnology

Selectivity controlled transformation of carbon dioxide into a versatile bi-functional multi-carbon oxygenate using a physically mixed ruthenium–iridium catalyst

The efficiency of supercritical CO₂ (scCO₂) as a reactant was successfully unfolded in the synthesis of a high-value C₂₊ oxygenate via hydrogenation and C–C bond formation under comparatively mild conditions.

Promising Catalytic Systems for CO2 Hydrogenation into CH4: A Review of Recent Studies

The increasing utilization of renewable sources for electricity production turns CO2 methanation into a key process in the future energy context, as this reaction allows storing the temporary renewable electricity surplus in the natural gas network (Power-to-Gas). This kind of chemical reaction requires the use of a catalyst and thus it has gained the attention of many researchers thriving to achieve active, selective and stable materials in a remarkable number of studies. The existing papers published in literature in the past few years about CO2 methanation tackled the catalysts composition and their related performances and mechanisms, which served as a basis for researchers to further extend their in-depth investigations in the reported systems. In summary, the focus was mainly in the enhancement of the synthesized materials that involved the active metal phase (i.e., boosting its dispersion), the different types of solid supports, and the frequent addition of a second metal oxide (usually behaving as a promoter). The current manuscript aims in recapping a huge number of trials and is divided based on the support nature: SiO2, Al2O3, CeO2, ZrO2, MgO, hydrotalcites, carbons and zeolites, and proposes the main properties to be kept for obtaining highly efficient carbon dioxide methanation catalysts.

Hydrogenation of Carbon Dioxide to Methanol over Non-Cu-based Heterogeneous Catalysts

The increasing atmospheric CO₂ level makes CO₂ reduction an urgent challenge facing the world. Catalytic transformation of CO₂ into chemicals and fuels utilizing renewable energy is one of the promising approaches toward alleviating CO₂ emissions. In particular, the selective hydrogenation of CO₂ to methanol utilizing renewable hydrogen potentially enables large scale transformation of CO₂ . The Cu-based catalysts have been extensively investigated in CO₂ hydrogenation. However, it is not only limited by long-term instability but also displays unsatisfactory catalytic performance. The supported metal-based catalysts (Pd, Pt, Au, and Ag) can achieve high methanol selectivity at low temperatures. The mixed oxide catalysts represented by M_a ZrO_x (M_a =Zn, Ga, and Cd) solid solution catalysts present high methanol selectivity and catalytic activity as well as excellent stability. This Review focuses on the recent advances in developing Non-Cu-based heterogeneous catalysts and current understandings of catalyst design and catalytic performance. First, the thermodynamics of CO₂ hydrogenation to methanol is discussed. Then, the progress in supported metal-based catalysts, bimetallic alloys or intermetallic compounds catalysts, and mixed oxide catalysts is discussed. Finally, a summary and a perspective are presented.

Engineering Heterostructured Nanocatalysts for CO2 Transformation Reactions: Advances and Perspectives

As a conceivable route to achieving anthropological carbon looping, carbon capture and utilization (CCU) technologies employ waste CO₂ as an accessible C1 building block to generate upgraded chemicals or fuels, thereby simultaneously remedying environmental issues and energy crises. However, efficient CO₂ conversion is disfavored by both its thermodynamics and its kinetics. Heterostructured materials with well-controlled interfaces have great potential for enhanced catalytic performance in various CO₂ transformation reactions, owing to the synergistic effects among components, numerous interfacial and/or surface active sites, increased CO₂ adsorption capacity, promoted charge transfer efficiency, and unique physicochemical properties. This Review highlights the state of the art in typical heterostructures, such as core-shell, yolk-shell, Janus, hierarchical (branched and hollow), and 2D/2D layered structures, applied for CO₂ conversion with various energy inputs (radiation, electricity, heat). Fabrication methods of different heterostructures and structure-composition-performance relationships are also discussed concisely. Finally, a brief summary and prospective research directions are provided. The motivation of this Review is to offer instructive information on the applicability of inorganic heterostructures for CO₂ transformation reactions, and it is hoped that further enlightening studies in this field could emerge in the future.

The Future of Carbon Dioxide Chemistry

The utilization of carbon dioxide as building block for chemicals or source of carbon for energy products has been explored for over 40 years now, with varying allure. In correspondence with oil-crises, the use of CO₂ has come into the spotlight, soon set aside when the crisis was over due to the low price of fossil carbon and the convenience of using established technologies. Nowadays, there is a continuous shift from fossil-C-based to perennial (solar, wind, geothermal, hydro-power) energy-driven processes that will also have a great potential to convert large amounts of carbon dioxide. The integration of biotechnology and catalysis will be a key player towards the utilization of CO₂ in several different applications, reducing both the extraction of fossil carbon and the carbon transfer to the atmosphere.

Silica-Related Catalysts for CO2 Transformation into Methanol and Dimethyl Ether

The climate situation that the planet is experiencing, mainly due to the emission of greenhouse gases, poses great challenges to mitigate it. Since CO2 is the most abundant greenhouse gas, it is essential to reduce its emissions or, failing that, to use it to obtain chemicals of industrial interest. In recent years, much research have focused on the use of CO2 to obtain methanol, which is a raw material for the synthesis of several important chemicals, and dimethyl ether, which is advertised as the cleanest and highest efficiency diesel substitute fuel. Given that the bibliography on these catalytic reactions is already beginning to be extensive, and due to the great variety of catalysts studied by the different research groups, this review aims to expose the most important catalytic characteristics to take into account in the design of silica-based catalysts for the conversion of carbon dioxide to methanol and dimethyl ether.

Construction of Thiazolo[5,4-d]thiazole-based Two-Dimensional Network for Efficient Photocatalytic CO2 Reduction

The efficient conversion of CO₂ to chemical fuels driven by solar energy is still a challenging research area in photosynthesis, in which the conversion efficiency greatly relies on photocatalytic coenzyme NADH regeneration. Herein, a photocatalyst/biocatalyst synergetic system based on a conjugated microporous polymer (CMP) was prepared for sustainable and highly selective photocatalytic reduction of CO₂ to methanol. Two thiazolo[5,4-d]thiazole-linked CMPs (TZTZ-TA and TZTZ-TP) were designed and synthesized as photocatalysts. Slight skeleton modification led to a great difference in their photocatalytic performance. Triazine-based TZTZ-TA exhibited an unprecedentedly high NADH regeneration efficiency of 82.0% yield within 5 min. Furthermore, the in situ photocatalytic NADH regeneration system could integrate with three consecutive enzymes for efficient conversion of CO₂ into methanol. This CMP-enzyme hybrid system provides a new avenue for accomplishing the liquid sunshine from CO₂.

Synthesis and Characterization of p-n Junction Ternary Mixed Oxides for Photocatalytic Coprocessing of CO2 and H2O

In the present paper, we report the synthesis and characterization of both binary (Cu2O, Fe2O3, and In2O3) and ternary (Cu2O-Fe2O3 and Cu2O-In2O3) transition metal mixed-oxides that may find application as photocatalysts for solar driven CO2 conversion into energy rich species. Two different preparation techniques (High Energy Milling (HEM) and Co-Precipitation (CP)) are compared and materials properties are studied by means of a variety of characterization and analytical techniques UV-Visible Diffuse Reflectance Spectroscopy (UV-VIS DRS), X-ray Photoelectron Spectroscopy (XPS), X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM), and Energy Dispersive X-Ray spectrometry (EDX). Appropriate data elaboration methods are used to extract materials bandgap for Cu2O@Fe2O3 and Cu2O@In2O3 prepared by HEM and CP, and foresee whether the newly prepared semiconductor mixed oxides pairs are useful for application in CO2-H2O coprocessing. The experimental results show that the synthetic technique influences the photoactivity of the materials that can correctly be foreseen on the basis of bandgap experimentally derived. Of the mixed oxides prepared and described in this work, only Cu2O@In2O3 shows positive results in CO2-H2O photo-co-processing. Preliminary results show that the composition and synthetic methodologies of mixed-oxides, the reactor geometry, the way of dispersing the photocatalyst sample, play a key role in the light driven reaction of CO2–H2O. This work is a rare case of full characterization of photo-materials, using UV-Visible DRS, XPS, XRD, TEM, EDX for the surface and bulk analytical characterization. Surface composition may not be the same of the bulk composition and plays a key role in photocatalysts behavior. We show that a full material knowledge is necessary for the correct forecast of their photocatalytic behavior, inferred from experimentally determined bandgaps.

Recent Advances in Supported Metal Catalysts and Oxide Catalysts for the Reverse Water-Gas Shift Reaction

The reverse water-gas shift reaction (RWGSR), a crucial stage in the conversion of abundant CO2 into chemicals or hydrocarbon fuels, has attracted extensive attention as a renewable system to synthesize fuels by non-traditional routes. There have been persistent efforts to synthesize catalysts for industrial applications, with attention given to the catalytic activity, CO selectivity, and thermal stability. In this review, we describe the thermodynamics, kinetics, and atomic-level mechanisms of the RWGSR in relation to efficient RWGSR catalysts consisting of supported catalysts and oxide catalysts. In addition, we rationally classify, summarize, and analyze the effects of physicochemical properties, such as the morphologies, compositions, promoting abilities, and presence of strong metal-support interactions (SMSI), on the catalytic performance and CO selectivity in the RWGSR over supported catalysts. Regarding oxide catalysts (i.e., pure oxides, spinel, solid solution, and perovskite-type oxides), we emphasize the relationships among their surface structure, oxygen storage capacity (OSC), and catalytic performance in the RWGSR. Furthermore, the abilities of perovskite-type oxides to enhance the RWGSR with chemical looping cycles (RWGSR-CL) are systematically illustrated. These systematic introductions shed light on development of catalysts with high performance in RWGSR.

Exploration of New Biomass-Derived Solvents: Application to Carboxylation Reactions

A range of hitherto unexplored biomass-derived chemicals have been evaluated as new sustainable solvents for a large variety of CO2 -based carboxylation reactions. Known biomass-derived solvents (biosolvents) are also included in the study and the results are compared with commonly used solvents for the reactions. Biosolvents can be efficiently applied in a variety of carboxylation reactions, such as Cu-catalyzed carboxylation of organoboranes and organoboronates, metal-catalyzed hydrocarboxylation, borocarboxylation, and other related reactions. For many of these reactions, the use of biosolvents provides comparable or better yields than the commonly used solvents. The best biosolvents identified are the so far unexplored candidates isosorbide dimethyl ether, acetaldehyde diethyl acetal, rose oxide, and eucalyptol, alongside the known biosolvent 2-methyltetrahydrofuran. This strategy was used for the synthesis of the commercial drugs Fenoprofen and Flurbiprofen.

Synthesis of Fluorinated Dialkyl Carbonates from Carbon Dioxide as a Carbonyl Source

Fluorinated dialkyl carbonates (DACs), which serve as environmentally benign phosgene substitutes, were produced successfully from carbon dioxide either directly or indirectly. Nucleophilic addition of 2,2,2-trifluoroethanol to carbon dioxide and subsequent reaction with 2,2,2-trifluoroethyltriflate (3 a) afforded bis(2,2,2-trifluoroethyl) carbonate (1) in up to 79 % yield. Additionally, carbonate 1 was obtained through the stoichiometric reaction of 3 a and cesium carbonate. Although bis(1,1,1,3,3,3-hexafluoro-2-propyl) carbonate (4) was difficult to obtain by either of the above two methods, it could be synthesized through the transesterification of carbonate 1.

An Efficient and Practical System for the Synthesis of N,N-Dimethylformamide by CO2 Hydrogenation using a Heterogeneous Ru Catalyst: From Batch to Continuous Flow

In the context of CO₂ utilization, a number of CO₂ conversion methods have been identified in laboratory-scale research; however, only a very few transformations have been successfully scaled up and implemented industrially. The main bottleneck in realizing industrial application of these CO₂ conversions is the lack of industrially viable catalytic systems and the need for practically implementable process developments. In this study, a simple, highly efficient and recyclable ruthenium-grafted bisphosphine-based porous organic polymer (Ru@PP-POP) catalyst has been developed for the hydrogenation of CO₂ to N,N-dimethylformamide, which affords a highest ever turnover number of 160 000 and an initial turnover frequency of 29 000 h^-1 in a batch process. The catalyst is successfully applied in a trickle-bed reactor and utilized in an industrially feasible continuous-flow process with an excellent durability and productivity of 915 mmol h^-1  g_Ru ^-1 .

Aluminum complexes with new non-symmetric ferrocenyl amidine ligands and their application in CO2 transformation into cyclic carbonates

A set of alkyl aluminum complexes supported by non-symmetric ferrocenyl amidine ligands were used as catalysts for the preparation of cyclic carbonates from epoxides and carbon dioxide using Bu₄NI as a co-catalyst.

Core–shell structured catalysts for thermocatalytic, photocatalytic, and electrocatalytic conversion of CO2

An in-depth assessment of properties of core–shell catalysts and their application in the thermocatalytic, photocatalytic, and electrocatalytic conversion of CO₂into synthesis gas and valuable hydrocarbons.

State of the art and perspectives in heterogeneous catalysis of CO2 hydrogenation to methanol

The ever-increasing amount of anthropogenic carbon dioxide (CO₂) emissions has resulted in great environmental impacts, the heterogeneous catalysis of CO₂ hydrogenation to methanol is of great significance.

Mechanistic study on the regioselective Ni-catalyzed dicarboxylation of 1,3-dienes with CO2

DFT calculations revealed a new CO₂ insertion mode different from conventional mechanisms in the Ni-catalyzed dicarboxylation of 1,3-dienes.

Toward Efficient Carbon and Water Cycles: Emerging Opportunities with Single-Site Catalysts Made of 3d Transition Metals

Advances in the chemical and electrochemical transformation of carbon and water are vital for delivering affordable and environmentally friendly energy sources and chemicals. Central to this challenge is the performance of materials. Traditionally, noble metal particles or metal complexes have been used as catalysts for many reactions. Recently, 3d transition-metal single-site catalysts (3dTM-SSCs) have emerged as potentially transformational candidates for the next-generation high-performance noble-metal-free catalysts. Designing catalysts at the molecular level can lead to a more efficient utilization of metal atoms and at the same time enhance catalytic performance under harsh reaction conditions. Despite this promise, several fundamental issues remain, in particular the structural evolution of 3dTM-SSCs during the synthesis, the molecular-level insights into the structure of the active sites, catalytic mechanisms, and the long-term cycling stability. Here, the material chemistries that facilitate the 3dTM-SSCs generation through a controlled pyrolytic synthesis are discussed, with focus on elucidating the underlying performance descriptors that can tune the catalytic properties in various critical reactions in carbon and water cycles. The current challenges and possible solutions for improving these novel catalytic materials are also highlighted.

Metal-Free Photocatalytic Synthesis of exo-Iodomethylene 2-Oxazolidinones: An Alternative Strategy for CO2 Valorization with Solar Energy

A visible-light-promoted metal-free carboxylative cyclization of propargylic amines with CO₂ was shown to offer exo-iodomethylene 2-oxazolidinones. Incorporation of both CO₂ and iodo moieties into these compounds was realized efficiently. The mechanism study revealed that this carboxylative cyclization proceeds through a radical pathway. Notably, the iodine-functionalized 2-oxazolidinone as a platform molecule could be easily converted into a wide range of value-added chemicals through Buchwald-Hartwig, Suzuki, Sonogashira, photocatalytic ene, and photoreduction reactions. As a result, the plentiful downstream transformations remarkably enhance the range of chemicals derived from CO₂ and open a potential avenue for CO₂ functionalization to circumvent energy challenges in this field.

Tandem Reactions of CO2 Reduction and Ethane Aromatization

Aromatization of light alkanes is of great interest because this can expand the raw materials used to produce aromatics to include fractions of natural gas that are readily available and inexpensive. Combining CO₂ reduction with ethane dehydrogenation and aromatization can also mitigate CO₂ emissions. A one-step process that can produce liquid aromatics from the reactions of CO₂ and ethane using phosphorus (P)- and gallium (Ga)-modified ZSM-5 has been evaluated at 873 K and atmospheric pressure. The addition of P improves the hydrothermal stability of Ga/ZSM-5, reduces coke formation on the catalyst surface, and allows the formation of more liquid aromatics through the tandem reactions of CO₂-assisted oxidative dehydrogenation of ethane and subsequent aromatization. Density functional theory calculations provide insights into the effect of Ga- and P- modification on ethane dehydrogenation to ethylene as well as the role of CO₂ on the production of aromatics.

Production of Sodium Bicarbonate from CO2 Reuse Processes: A Brief Review

Research activities discuss about the global environmental impacts of carbon dioxide (CO2) emissions. Government authorities and international conferences aim to reduce greenhouse gas emissions and encourage the development of sustainable processes using renewable sources. In order to reduce emissions from the industrial sector, CO2 capture and reuse as a raw material in the production of marketable products have encouraged the development of technologies. Among many possible chemical products manufactured from CO2, sodium bicarbonate appears in this context as an important compound in the chemical, food, textile and pharmaceutical industries. Then, the main objective of this work was to carry out a bibliographical review of the main production processes available in the literature for synthesis of sodium bicarbonate and the main chemical reactions involved in the crystallization reactor. Regarding to the processes, soda ash carbonation from trona, the Solvay process and the sodium sulfate route were assessed and compared. Among the main raw materials used in the production process of sodium bicarbonate, sodium chloride is presented as most economically feasible while sodium carbonate and sodium sulfate are indicated as the most environmentally viable alternatives. Beyond, the global processes were presented for each route discussing advantages and disadvantages for the separation and purification steps required after the reaction. It is notable that the main raw material is sodium chloride due to its easy possibility of obtaining, from seawater, and large availability for applications at the food industry. Indeed, the production of sodium bicarbonate by means of the Solvay process was the route that presented the best results regarding to the technology development and economic cost. Use of sodium sulfate as raw material has proved to be a possible route, besides presenting numerous advantages such as production of valuable byproducts. However, this route may be not totally viable compared to conventional routes due to the complexity of products separation and purification. The review showed that there is a lack in the scientific literature regarding to the development of studies evaluating sodium bicarbonate crystallization and purification in a cost effective and technical detailed approach.

The Changing Role of CO2 in the Transition to a Circular Economy: Review of Carbon Sequestration Projects

Despite the diversity of studies on global warming and climate change mitigation technologies, research on the changing role of CO2 in the industrial processes, which is connected with the introduction of circular economy principles, is still out of scope. The purpose of this review is to answer the following question: Is technogenic CO2 still an industrial waste or has it become a valuable resource? For this purpose, statistical information from the National Energy Technology Library and the Global CCS Institute databases were reviewed. All sequestration projects (199) were divided into three groups: carbon capture and storage (65); carbon capture, utilization, and storage (100); and carbon capture and utilization (34). It was found that: (1) total annual CO2 consumption of such projects was 50.1 Mtpa in 2018, with a possible increase to 326.7 Mtpa in the coming decade; (2) total amount of CO2 sequestered in such projects could be 2209 Mt in 2028; (3) the risk of such projects being cancelled or postponed is around 31.8%; (4) CO2 is a valuable and sought-after resource for various industries. It was concluded that further development of carbon capture and utilization technologies will invariably lead to a change in attitudes towards CO2, as well as the appearance of new CO2-based markets and industries.

Insertion of CO2 Mediated by a (Xantphos)NiI -Alkyl Species

The incorporation of CO₂ into organometallic and organic molecules represents a sustainable way to prepare carboxylates. The mechanism of reductive carboxylation of alkyl halides has been proposed to proceed through the reduction of Ni^II to Ni^I by either Zn or Mn, followed by CO₂ insertion into Ni^I -alkyl species. No experimental evidence has been previously established to support the two proposed steps. Demonstrated herein is that the direct reduction of (tBu-Xantphos)Ni^II Br₂ by Zn affords Ni^I species. (tBu-Xantphos)Ni^I -Me and (tBu-Xantphos)Ni^I -Et complexes undergo fast insertion of CO₂ at 22 °C. The substantially faster rate, relative to that of Ni^II complexes, serves as the long-sought-after experimental support for the proposed mechanisms of Ni-catalyzed carboxylation reactions.

Novel porous organocatalysts for cycloaddition of CO2 and epoxides

Three classes of organosilicas (DMO, OMOs and PMOs) containing immobilized multi-hydroxyl bis-(quaternary ammonium) iodide salts were prepared and tested in the cycloaddition of CO₂ and epoxides. Owing to its higher surface area, pore volume and optimum nucleophilicity of the iodide ion, OMO-2 with two hydroxyl groups was found to be the most active catalyst. For substrates that are easy to activate such as propylene oxide, 1,2-epoxybutane and epichlorohydrin, excellent yields and selectivities were obtained under mild reaction conditions (0.5 MPa CO₂, 50 °C and 10-15 h). Moreover, OMO-2 showed very good catalytic properties (yield ≥ 93% and selectivity ≥ 98%), and excellent chemical and textural stability in the synthesis of 1,2-butylene carbonate over 5 cycles.

Life Cycle Assessment for the Organocatalytic Synthesis of Glycerol Carbonate Methacrylate

Bifunctional ammonium and phosphonium salts have been identified as potential organocatalysts for the synthesis of glycerol carbonate methacrylate (GCMA). Three of these catalysts showed high efficiency and allowed the conversion of glycidyl methacrylate with CO₂ to the desired product in >99 % conversion and selectivity. Subsequently, immobilized analogues of selected catalysts were prepared and tested. A phenol-substituted phosphonium salt on a silica support proved to be a promising candidate in recycling experiments. The same catalyst was used in 12 consecutive runs, resulting in GCMA yields of up to 88 %. Furthermore, a life cycle assessment was conducted for the synthesis of GCMA starting from epichlorohydrin (EPH) and methacrylic acid (MAA). For the functional unit of 1 kg GCMA, 15 wt % was attributed to the incorporation of CO₂ , which led to a reduction of the global warming potential of 3 % for the overall process.