Advances in CO2 Utilization

Metal–organic framework (MOF)-based catalysts have attracted significant attentions for their distinguished characteristics in CO₂ conversion, such as very high surface area, recyclability, permanent porosity, and multiple active sites. Although numerous publications have emerged in recent years focusing on MOFs and their catalytic properties in CO₂ conversion, this chapter specifically emphasizes the enhancement of MOF-based catalysts through micro/macrostructure and multicomponent design. The challenges encountered in MOFs-based CO₂ conversion and the essential requirements for practical catalytic applications are addressed. A brief summary of strategies is provided for designing catalysts with desired microstructure, macrostructure, and multicomponent characteristics by using MOFs as precursors. The latest progresses in novel MOF and MOF-derived catalysts with complex structures, specific compositions, and improved MOF stability for CO₂ conversion are also reviewed. The broad application prospects of MOF-based catalysts in CO₂ conversion are introduced, including CO₂ organic transformation, hydrogenation, photocatalysis, electrocatalysis, and photoelectroreduction. Moreover, the challenges faced in the practical application of MOF-based catalysts in CO₂ conversion are presented, and the promising future directions are outlined.

Photo-thermo catalysis serves as a novel strategy for CO₂ conversion, wherein enhanced activity, manipulated selectivity and/or improved stability can be achieved with synergisms between photocatalysis and thermocatalysis. To clarify fundamental issues and promote innovative development in this new field, comprehensive summarization and up-to-date perspective have been presented herein. Specifically, the conception, principles and operating mechanisms of photo-thermo catalysis have been systematically discussed, which has been followed by thorough analysis of representative examples in photo-thermo CO₂ conversion. Moreover, challenges and perspectives have been proposed as implications for future development. Overall, this book chapter is expected to clear up theoretical basis and set up practical guidelines for photo-thermo catalytic conversion of CO₂.

Thermocatalytic CO₂ hydrogenation to liquid fuels, including ethanol and liquid hydrocarbons, has drawn global attention recently as a potential strategy to decrease CO₂ emissions and reduce the consumption of and dependence on fossil fuels. The nature of catalyst has an important impact on the conversion and selectivity and clarifying the catalyst structure-performance relationship is essential to synthesize the desired liquid products. Compared with C₁ products, the generation of ethanol and liquid hydrocarbons with two or more carbon atoms is more difficult owing to the high energy barrier for C–C coupling. Current studies show that the interfacial catalysts are suitable for CO₂ hydrogenation to ethanol and the active interface is generally responsible for key CO^* insertion, while the metal/carbide catalysts and oxide-zeolite tandem catalysts play vital roles in that to liquid hydrocarbons. In this chapter, we discuss the latest advances in the representative noble metals, transition metals and their carbides, and modified Cu-based catalysts for the synthesis of ethanol, Fe–, Co-based catalysts as well as tandem catalysts for that of long-chain hydrocarbons. Fundamental understanding on active sites, structural evolution, CO₂ activation, and reaction mechanism are discussed based on computational and experimental results. On this basis, we discuss some concepts on catalyst design as well as the challenges and opportunities for its development and potential industrial applications.

To ensure sustainable development in the chemical industry, new catalytic materials and large-scale processes are required for minimizing the carbon footprint. Many efforts have been made in the valorization of carbon dioxide (CO₂), the primary greenhouse gas, through thermo-, electro-, and photocatalysis over the past decades. Within this concept, the direct hydrogenation of CO₂ with hydrogen (H₂) produced on a CO₂-free basis has been attracting a special attention due to its high efficiency to close carbon cycles. Among various products formed through CO₂ hydrogenation, methanol (CH₃OH) and carbon monoxide (CO) stand out due to their multiple applications as platform chemicals. The former is also used as a fuel with high energy density. This contribution critically analyzes the up-to now developed catalysts for CO₂ hydrogenation to methanol or CO via thermo catalytic processes, with a special focus being put on the discussion of active phases/sites and structure–activity relationships reported in previous studies. The suggested reaction mechanisms considering both selective and side reactions over different catalysts have also been briefly reviewed.

Increasing research interests can be found in supported Ni catalyst for CO₂ methanation because of the low price of the metal with comparable activity to the noble metal catalysts. CO₂ methanation on Ni catalyst shows high CO₂ conversion with high selectivity of methane at temperatures around 300 °C at atmospheric pressure. The established pipelines for transportation of natural gas can be directly used for the methane product. CO₂ methanation on Ni catalyst has a big potential in the large-scale utilization of carbon dioxide. CO₂ methanation over the Ni catalyst is a structure-sensitive reaction, with which the mechanism is still in debate. It remains a big challenge in the structural controllable preparation of the supported Ni catalyst. In this chapter, recent advances in the studies of structural effect of the supported Ni catalyst on CO₂ methanation were summarized. Future development is also discussed.

Direct CO₂ reforming with light alkanes is a promising approach for transforming CO₂ into value-added products, enabling carbon emission reduction and valorization (to reduce the reliance on fossil fuels). The development of highly active and stable catalytic systems is essential for the cost-effective and practical CO₂ reforming processes. In this chapter, we first summarized the state-of-the-art on the catalyst design for CO₂ reforming mainly regarding the support selection and structure modification to tackle the catalytic deactivation issues such as metal sintering or coke formation. Additionally, other advanced CO₂ reforming systems such as super-dry reforming and photocatalysis are discussed as well since they have the potential to activate the CO₂ conversion processes either with ultra-high CO₂ utilization efficiency or under milder conditions. Finally, recent developments on in situ/operando characterization techniques for mechanistic investigations are presented, which is beneficial for the rational design/optimization of catalysts to advance catalytic CO₂ reforming technologies.

CO₂RR electrocatalysis is a key technology/process for transformative (industrial) chemical production but requires accelerating the development of novel materials and approaches by turning the current design strategies. This contribution does not review this topic but instead highlights pitfalls and scientific gaps in the current approaches. The discussion is focused on electrode/reactor engineering and related aspects, including how to control the nanoffenvironment at the electrocatalyst surface. Their better understanding, especially the development of reliable modelling able to account for the complexity of the phenomena present in electrocatalysis, is the condition to accelerate the progress. It is also remarked that the mechanistic and design strategies used have an intrinsic methodological issue. Approaching catalysis from the perspective of selectively transferring energy for the activation barriers rather than only considering the nature of the active sites and the energetic pathways of transformation (the current approach) is discussed. The concept is related to the role of localised phonons, polarons and interaction with excitons in determining the CO₂ electrocatalytic conversion pathways.

The world today is experiencing adverse effects of climate change due to the escalated levels of greenhouse gases such as CO₂ in the atmosphere. Consequently, there is an urgent need for minimizing the CO₂ level to tackle climate change. Utilization of CO₂ for synthesizing valuable commodities, such as biofuel and biochemical, is an effective strategy toward mitigating climate change as well as the energy crisis. Moreover, the conversion of CO₂ into valuable products is also a promising step for achieving carbon neutrality and exemplifying a circular economy. In this regard, several methods, such as physical, chemical, and biological, are available for the utilization and conversion of CO₂. However, biological methods for the conversion of CO₂ into biofuels and biochemicals are more sustainable as they are environmentally friendly and cost-effective compared to the chemical methods. Thus, in this chapter, different CO₂ bioconversion processes with their efficacy and their limitations have been discussed. Besides this, future developments in terms of CO₂ bioconversion have also been presented for alleviating the limitations, so that the production of biocommodities from CO₂ can be achieved at a large scale.

The polymeric materials could be synthesized directly from CO₂ as a monomer, which are named as CO₂-sourced polymers, mainly including polyurethane, polyurea, polycarbonate, and polyester. The CO₂-sourced polymers are of some advantages compared to their conventional counterparts, such as environmental benignity without using toxic reagents, carbon reduction, degradability, and reproducibility. This chapter will review the advancements achieved in the CO₂-sourced polymer synthesized directly and indirectly by using CO₂ as a monomer over the past five years (from 2019 to present). Herein, we pay main attention to the synthetic methodologies, the structure, properties, and possible applications of several kinds of important CO₂-sourced polymers such as polyurethanes, polyureas, polycarbonates, and polyesters.

This chapter discusses the applications of plasma and plasma catalysis for CO₂ conversion. After a general introduction on plasma technology and why it is interesting for CO₂ conversion, we briefly explain the most common plasma reactor types used for this application. Subsequently, we present the state-of-the-art on plasma-based CO₂ conversion including dry reforming of methane (CH₄) (DRM) in these different types of plasma reactors. This will be followed by the state-of-the-art on plasma catalysis for CO₂ conversion, including CO₂ splitting, CO₂ hydrogenation, DRM, and CO₂ reduction with water.

Carbon dioxide (CO₂), a resourceful, renewable, and non-toxic C₁ resource, is of great significance if applied to produce value-added chemicals. In recent years, CO₂ valorization has been well exploited as expected. Among them, functionalizing organic substrates with CO₂ to synthesize high value-added carboxylic acid compounds is extremely attractive. Since carboxylic acids and its derivatives are essential structural motifs in pharmaceuticals, pesticides, fine chemicals, commodities, and natural products. Moreover, dicarboxylic acids are very appealing monomers for the manufacture of functional plastics and rubbers. Therefore, considerable efforts have been devoted to developing synthetic methods of carboxylic acids and expanding their applications. Notably, carboxylation reactions of unsaturated organic compounds (e.g., alkenes, alkynes, aromatic hydrocarbons) with CO₂ catalyzed by transition metals have been regarded as an efficacious way to synthesize diverse functionalized carboxylic acids and its derivatives. In this chapter, we summarize the advancement of carboxylation reactions of unsaturated compounds such as (1) carboxylation of C–H bond, (2) heterocarboxylation, (3) hydrocarboxylation, and (4) dicarboxylation, promoted by transition metal complexes such as Ni, Cu, Pd, Au, Rh, and so on. We are focusing on their rationales behind and several kinds of important products which include aryl carboxylic acid, α, β-unsaturated carboxylic acid, functionalized carboxylic acid, and dicarboxylic acid.

Carbon dioxide can be used as building block for chemicals or source of carbon for energy products (fuels). The latter have a market that is over fifteen times that of chemicals and are, thus, of greater interest for the large-scale implementation of the CCU strategy (capture and utilization of CO₂). The drawback is that while the chemical use of CO₂ may not require neither an energy input nor hydrogen, the conversion of CO₂ into fuels requires both energy and hydrogen that cannot be derived from fossil-C. The solution is the use of C-free primary energy sources for powering the reduction process and water as source of hydrogen or, even better, of protons and electrons. Noteworthy, the reduction of CO₂ may either use H₂ or, alternatively, may be implemented avoiding the production and use of molecular hydrogen, mimicking nature that uses the proton-coupled to electron transfer-PCET strategy. In this chapter, the putative technologies that may promote a carbon cyclic economy (CCE) are discussed together with their readiness (on the short- to long-term) and degree of innovation. Technical barriers to the scale-up of electrolyzers for H₂ production are discussed, considering the existing options: AWE, PME, HTWE. Routes to avoiding H₂ production (either the electrolysis of CO₂ in water or the photochemical- or photo-electro-chemical co-processing of H₂O and CO₂) are analyzed. The direct use of solar energy is considered both at ambient temperature (co-processing of CO₂ and H₂O under solar irradiation), or at high temperature (processes based on the use of solar power concentrators-SPC). The analysis of the TRL of the various technologies concludes the discussion. A deep technological innovation that may improve the efficiency in the production and use of e-fuels or solar fuels is necessary for a real reduction of the impact of the chemical and energy sectors on climate change. Whether the substitution of H₂ for C-based fuels is a real benefit for climate is questioned.