A Carbon-Neutral CO2 Capture, Conversion, and Utilization Cycle with Low-Temperature Regeneration of Sodium Hydroxide

Integrated Carbon Dioxide Capture and Conversion to Methanol Utilizing Tertiary Amines over a Heterogenous Cu/ZnO/Al2O3 Catalyst

Increasing carbon dioxide emissions has sparked a growing interest in capturing these emissions at the source of their release. For such processes, amines can be used as carbon dioxide capture agents. Herein, CO2 was captured under ambient conditions using solutions of amines and polyamines in ethylene glycol. The captured solutions were then successfully hydrogenated to methanol under hydrogen pressure with a heterogeneous Cu/ZnO/Al2O3 industrial catalyst. An extensive amine scope found that tetramethyl-1,6-hexanediamine, with two tertiary amine sites, provided the highest methanol productivity. This reaction was then optimized to achieve up to 89% methanol yield under relatively mild conditions of 250 °C and 80 bar H2 pressure. The catalyst was shown to be recyclable over five reaction cycles.

Novel heterogeneous Fe-based catalysts for carbon dioxide hydrogenation to long chain α-olefins-A review

The thermocatalytic conversion of carbon dioxide (CO2) into high value-added chemicals provides a strategy to address the environmental problems caused by excessive carbon emissions and the sustainable production of chemicals. Significant progress has been made in the CO2 hydrogenation to long chain α-olefins, but controlling C-O activation and C-C coupling remains a great challenge. This review focuses on the recent advances in catalyst design concepts for the synthesis of long chain α-olefins from CO2 hydrogenation. We have systematically summarized and analyzed the ingenious design of catalysts, reaction mechanisms, the interaction between active sites and supports, structure-activity relationship, influence of reaction process parameters on catalyst performance, and catalyst stability, as well as the regeneration methods. Meanwhile, the challenges in the development of the long chain α-olefins synthesis from CO2 hydrogenation are proposed, and the future development opportunities are prospected. The aim of this review is to provide a comprehensive perspective on long chain α-olefins synthesis from CO2 hydrogenation to inspire the invention of novel catalysts and accelerate the development of this process.

Expanding the Library of Ions for Moisture-Swing Carbon Capture

Developing materials that can more efficiently and cheaply capture carbon dioxide from ambient atmospheric conditions is essential for improving negative emission technologies. This study builds on the promising moisture-swing modality for direct air capture of carbon dioxide by investigating the use of several new anions─orthosilicate, borate, pyrophosphate, tripolyphosphate, and dibasic phosphate─that when introduced into ion-exchange resins allow for the cyclable capture of CO2 under dry conditions and its release under wet conditions. These ions, as well as many others that failed to show moisture-swing performance, are tested and directly compared thermodynamically and kinetically to understand their differences. This includes the use of analytical approaches new to the carbon capture field, such as the correlation of adsorption isotherms to moisture-swing performance, the use of phase lag kinetics, the examination of the humidity-carbon capture hysteresis of the sorbents, and the precise quantification of ion loading using inductively coupled plasma-optical emission spectroscopy. Phosphate dibasic was found to have the largest mass-normalized CO2 moisture-swing capacity, whereas phosphate tribasic had the best performance when factoring in kinetics, and pyrophosphate had the highest swing capacity when normalizing on a per-ion or per-unit-charge basis. This work not only sheds light on ways to improve DAC but also provides insights pertinent to the advancement of gas separation, negative emission technologies, and sorbent materials.

Directly Knitted Hierarchical Porous Organometallic Polymer-Based Self-Supported Single-Site Catalyst for CO2 Hydrogenation in Water

In recent times, heterogenization of homogeneous molecular catalysts onto various porous solid support structures has attracted significant research focus as a method for combining the advantages of both homogeneous as well as heterogeneous catalysis. The design of highly efficient, structurally robust and reusable heterogenized single-site catalysts for the CO2 hydrogenation reaction is a critical challenge that needs to be accomplished to implement a sustainable and practical CO2 -looped renewable energy cycle. This study demonstrated a heterogenized catalyst [Ir-HCP-(B/TPM)] containing a molecular Ir-abnormal N-heterocyclic carbene (Ir-aNHC) catalyst self-supported by hierarchical porous hyper-crosslinked polymer (HCP), in catalytic hydrogenation of CO2 to inorganic formate (HCO2 - ) salt that is a prospective candidate for direct formate fuel cells (DFFC). By employing this unique and first approach of utilizing a directly knitted HCP-based organometallic single-site catalyst for CO2 -to-HCO2 - in aqueous medium, extremely high activity with a single-run turnover number (TON) up to 50816 was achieved which is the highest so far considering all the heterogeneous catalysts for this reaction in water. Additionally, the catalyst featured excellent reusability furnishing a cumulative TON of 285400 in 10 cycles with just 1.6 % loss in activity per cycle. Overall, the new catalyst displayed attributes that are important for developing tangible catalysts for practical applications.

Versatile CO2 Hydrogenation-Dehydrogenation Catalysis with a Ru-PNP/Ionic Liquid System

High catalytic activities of Ru-PNP [Ru = ruthenium; PNP = bis alkyl- or aryl ethylphosphinoamine complexes in ionic liquids (ILs) were obtained for the reversible hydrogenation of CO₂ and dehydrogenation of formic acid (FA) under exceedingly mild conditions and without sacrificial additives. The novel catalytic system relies on the synergic combination of Ru-PNP and IL and proceeds with CO₂ hydrogenation already at 25 °C under a continuous flow of 1 bar of CO₂/H₂ (1:5), leading to 14 mol % FA with respect to the IL. A pressure of 40 bar of CO₂/H₂ (1:1) provides 126 mol % of FA/IL corresponding to a space-time yield (STY) of FA of 0.15 mol L^-1 h^-1. The conversion of CO₂ contained in imitated biogas was also achieved at 25 °C. Furthermore, the Ru-PNP/IL system catalyzes FA dehydrogenation with average turnover frequencies up to 11,000 h^-1 under heat-integrated conditions for proton-exchange membrane fuel cell applications (<100 °C). Thus, 4 mL of a 0.005 M Ru-PNP/IL system converted 14.5 L FA over 4 months with a turnover number exceeding 18,000,000 and a STY of CO₂ and H₂ of 35.7 mol L^-1 h^-1. Finally, 13 hydrogenation/dehydrogenation cycles were achieved with no sign of deactivation. These results demonstrate the potential of the Ru-PNP/IL system to serve as a FA/CO₂ battery, a H₂ releaser, and a hydrogenative CO₂ converter.

Homogeneous Hydrogenation of CO2 and CO to Methanol: The Renaissance of Low-Temperature Catalysis in the Context of the Methanol Economy

The traditional economy based on carbon-intensive fuels and materials has led to an exponential rise in anthropogenic CO₂ emissions. Outpacing the natural carbon cycle, atmospheric CO₂ levels increased by 50 % since the pre-industrial age and can be directly linked to global warming. Being at the core of the proposed methanol economy pioneered by the late George A. Olah, the chemical recycling of CO₂ to produce methanol, a green fuel and feedstock, is a prime channel to achieve carbon neutrality. In this direction, homogeneous catalytic systems have lately been a major focus for methanol synthesis from CO₂ , CO and their derivatives as potential low-temperature alternatives to the commercial processes. This Review provides an account of this rapidly growing field over the past decade, since its resurgence in 2011. Based on the critical assessment of the progress thus far, the present key challenges in this field have been highlighted and potential directions have been suggested for practically viable applications.

Homogeneous Carbon Capture and Catalytic Hydrogenation: Toward a Chemical Hydrogen Battery System

Recent developments of CO₂ capture and subsequent catalytic hydrogenation to C1 products are discussed and evaluated in this Perspective. Such processes can become a crucial part of a more sustainable energy economy in the future. The individual steps of this catalytic carbon capture and usage (CCU) approach also provide the basis for chemical hydrogen batteries. Here, specifically the reversible CO₂/formic acid (or bicarbonate/formate salts) system is presented, and the utilized catalysts are discussed.

Computational mechanistic studies of ruthenium catalysed methanol dehydrogenation

Homogeneous ruthenium catalysed methanol dehydrogenation could become a key reaction for hydrogen production in liquid fuel cells. In order to improve existing catalytic systems, mechanistic insight is paramount in directing future studies. Herein, we describe what computational mechanistic research has taught us so far about ruthenium catalysed dehydrogenation reactions. In general, two mechanistic pathways can be operative in these reactions: a metal-centered or a metal-ligand cooperative (Noyori-Morris type) minimum energy reaction pathway (MERP). Discerning between these mechanisms on the basis of computational studies has proven to be highly input dependent, and to circumvent pitfalls it is important to consider several factors, such as solvent effects, metal-ligand cooperativity, alternative geometries, and complex electronic structures of metal centres. This Frontiers article summarizes the reported computational research performed on ruthenium catalyzed dehydrogenation reactions performed in the past decade, and serves as a guide for future research.

Simultaneous CO2 capture and functionalization: solvated electron precursors as novel catalysts

Metal complexes with diffuse solvated electrons (solvated electron precursors) are proposed as alternative catalysts for the simultaneous CO₂ capture and utilization. Quantum chemical calculations were used to study the reaction of CO₂ with H₂ and C₂H₄ to produce formic acid, methyldiol and δ-lactone. Mechanisms of a complete reaction pathway are found and activation barriers are reasonably low. The metal ligand complex readily reduces CO₂ and significantly stabilizes CO₂˙^-. Ligand identity minimally influences the reaction. Additional reactions and future strategies are proposed with the goal of inducing experimental interest.

Challenges and recent advancements in the transformation of CO2 into carboxylic acids: straightforward assembly with homogeneous 3d metals

Transformation of carbon dioxide (CO2) into valuable organic carboxylic acids is essential for maintaining sustainability. In this review, such CO2 thermo-, photo- and electrochemical transformations under 3d-transition metal catalysis are described from 2017 until 2022.

In Situ Phase Separation into Coupled Interfaces for Promoting CO2 Electroreduction to Formate over a Wide Potential Window

Bimetallic sulfides are expected to realize efficient CO₂ electroreduction into formate over a wide potential window, however, they will undergo in situ structural evolution under the reaction conditions. Therefore, clarifying the structural evolution process, the real active site and the catalytic mechanism is significant. Here, taking Cu₂ SnS₃ as an example, we unveiled that Cu₂ SnS₃ occurred self-adapted phase separation toward forming the stable SnO₂ @CuS and SnO₂ @Cu₂ O heterojunction during the electrochemical process. Calculations illustrated that the strongly coupled interfaces as real active sites driven the electron self-flow from Sn⁴⁺ to Cu⁺ , thereby promoting the delocalized Sn sites to combine HCOO* with H*. Cu₂ SnS₃ nanosheets achieve over 83.4 % formate selectivity in a wide potential range from -0.6 V to -1.1 V. Our findings provide insight into the structural evolution process and performance-enhanced origin of ternary sulfides under the CO₂ electroreduction.

The Review of Carbon Capture-Storage Technologies and Developing Fuel Cells for Enhancing Utilization

The amount of CO2 released in the atmosphere has been at a continuous surge in the last decade, and in order to protect the environment from global warming, it is necessary to employ techniques like carbon capture. Developing technologies like Carbon Capture Utilization and Storage aims at mitigating the CO2 content from the air we breathe and has garnered immense research attention. In this review, the authors have aimed to discuss the various technologies that are being used to capture the CO2 from the atmosphere, store it and further utilize it. For utilization, researchers have developed alternatives to make profits from CO2 by converting it into an asset. The development of newer fuel cells that consume CO2 in exchange for electrical power to drive the industries and produce valuable hydrocarbons in the form of fuel has paved the path for more research in the field of carbon utilization. The primary focus on the article is to inspect the environmental and economic feasibility of novel technologies such as fuel cells, different electrochemical processes, and the integration of artificial intelligence and data science in them, which are designed for mitigating the percentage of CO2 in the air.

Conformational Change of H64 and Substrate Transportation: Insight Into a Full Picture of Enzymatic Hydration of CO2 by Carbonic Anhydrase

The enzymatic hydration of CO₂ into HCO₃ ^- by carbonic anhydrase (CA) is highly efficient and environment-friendly measure for CO₂ sequestration. Here extensive MM MD and QM/MM MD simulations were used to explore the whole enzymatic process, and a full picture of the enzymatic hydration of CO₂ by CA was achieved. Prior to CO₂ hydration, the proton transfer from the water molecule (WT1) to H64 is the rate-limiting step with the free energy barrier of 10.4 kcal/mol, which leads to the ready state with the Zn-bound OH^-. The nucleophilic attack of OH^- on CO₂ produces HCO₃ ^- with the free energy barrier of 4.4 kcal/mol and the free energy release of about 8.0 kcal/mol. Q92 as the key residue manipulates both CO₂ transportation to the active site and release of HCO₃ ^-. The unprotonated H64 in CA prefers in an inward orientation, while the outward conformation is favorable energetically for its protonated counterpart. The conformational transition of H64 between inward and outward correlates with its protonation state, which is mediated by the proton transfer and the product release. The whole enzymatic cycle has the free energy span of 10.4 kcal/mol for the initial proton transfer step and the free energy change of -6.5 kcal/mol. The mechanistic details provide a comprehensive understanding of the entire reversible conversion of CO₂ into bicarbonate and roles of key residues in chemical and nonchemical steps for the enzymatic hydration of CO₂.

Strategies for Integrated Capture and Conversion of CO2 from Dilute Flue Gases and the Atmosphere

The integrated capture and conversion of CO₂ has the potential to make valorization of the greenhouse gas more economically competitive, by eliminating energy-intensive regeneration processes. However, integration is hindered by the extremely low concentrations of CO₂ present in the atmosphere (0.04 vol.%), and the presence of acidic gas contaminants, such as SO_x and NO_x , in flue gas streams. This Review summarizes the latest technological progress in the integrated capture and conversion of CO₂ from dilute flue gases and atmospheric air. In particular, the Review analyzes the correlation between material properties and their capture and conversion efficiency through hydrogenation, cycloaddition, and solar thermal-mediated electrochemical processes, with a focus on the types and quantities of product generated, in addition to their energy requirements. Prospects for commercialization are also highlighted and suggestions are made for future research.

An amino acid based system for CO2 capture and catalytic utilization to produce formates

Herein, we report a novel amino acid based reaction system for CO2 capture and utilization (CCU) to produce formates in the presence of the naturally occurring amino acid l-lysine. Utilizing a specific ruthenium-based catalyst system, hydrogenation of absorbed carbon dioxide occurs with high activity and excellent productivity. Noteworthy, following the CCU concept, CO2 can be captured from ambient air in the form of carbamates and converted directly to formates in one-pot (TON > 50 000). This protocol opens new potential for transforming captured CO2 from ambient air to C1-related products.

Recent Progress with Pincer Transition Metal Catalysts for Sustainability

Our planet urgently needs sustainable solutions to alleviate the anthropogenic global warming and climate change. Homogeneous catalysis has the potential to play a fundamental role in this process, providing novel, efficient, and at the same time eco-friendly routes for both chemicals and energy production. In particular, pincer-type ligation shows promising properties in terms of long-term stability and selectivity, as well as allowing for mild reaction conditions and low catalyst loading. Indeed, pincer complexes have been applied to a plethora of sustainable chemical processes, such as hydrogen release, CO2 capture and conversion, N2 fixation, and biomass valorization for the synthesis of high-value chemicals and fuels. In this work, we show the main advances of the last five years in the use of pincer transition metal complexes in key catalytic processes aiming for a more sustainable chemical and energy production.

Transfer hydrogenation of carbon dioxide via bicarbonate promoted by bifunctional C-N chelating Cp*Ir complexes

Metal-ligand cooperative Cp*Ir(iii) complexes derived from primary benzylic amines effectively promote transfer hydrogenation of atmospheric CO2 using 2-propanol at 80 °C. Isotope-labelling experiments strengthen that active Ir species can preferentially reduce bicarbonate congeners formed from CO2. The powerful transfer hydrogenation catalyst exhibits remarkable activity for the conversion of bicarbonates into formate salts with a turnover number up to 3200, even without H2 and CO2.

Industrial carbon dioxide capture and utilization: state of the art and future challenges

This review covers the sustainable development of advanced improvements in CO₂ capture and utilization.

Integrated CO2 Capture and Conversion to Formate and Methanol: Connecting Two Threads

The capture of CO₂ from concentrated emission sources as well as from air represents a process of paramount importance in view of the increasing CO₂ concentration in the atmosphere and its associated negative consequences on the biosphere. Once captured using various technologies, CO₂ is desorbed and compressed for either storage (carbon capture and storage (CCS)) or production of value-added products (carbon capture and utilization (CCU)). Among various products that can be synthesized from CO₂, methanol and formic acid are of high interest because they can be used directly as fuels or to generate H₂ on demand at low temperatures (<100 °C), making them attractive hydrogen carriers (12.6 and 4.4 wt % H₂ in methanol and formic acid, respectively). Methanol is already produced in huge quantities worldwide (100 billion liters annually) and is also a raw material for many chemicals and products, including formaldehyde, dimethyl ether, light olefins, and gasoline. The production of methanol through chemical recycling of captured CO₂ is at the heart of the so-called "methanol economy" that we have proposed with the late Prof. George Olah at our Institute. Recently, there has been significant progress in the low-temperature synthesis of formic acid (or formate salts) and methanol from CO₂ and H₂ using homogeneous catalysts. Importantly, several studies have combined CO₂ capture and hydrogenation, where captured CO₂ (including from air) was directly utilized to produce formate and CH₃OH without requiring energy intensive desorption and compression steps. This Account centers on that topic. A key feature in the combined CO₂ capture and conversion studies reported to date for the synthesis of formic acid and methanol is the use of an amine or alkali-metal hydroxide base for capturing CO₂, which can assist the homogeneous catalysts in the hydrogenation step. We start this Account by examining the combined processes where CO₂ is captured in amine solutions and converted to alkylammonium formate salts. The effect of amine basicity on the reaction rate is discussed along with catalyst recycling schemes. Next, methanol synthesis by this combined process, with amines as capturing agents, is explored. We also examine the system developments for effective catalyst and amine recycling in this process. We next go through the effect of catalyst molecular structure on methanol production while elucidating the main deactivating pathway involving carbonylation of the metal center. The recent advances in first-row transition metal catalysts for this process are also mentioned. Subsequently, we discuss the capture of CO₂ using hydroxide bases and conversion to formate salts. The regeneration of the hydroxide base (NaOH or KOH) at low temperatures (80 °C) in cation-conducting direct formate fuel cells is presented. Finally, we review the challenges in the yet unreported integrated CO₂ capture by hydroxide bases and conversion to methanol process.

Additive-free cobalt-catalysed hydrogenation of carbonates to methanol and alcohols

Homogeneously cobalt-catalyzed hydrogenation of cyclic and acyclic carbonates: beneficial effects of 2,2,2-trifluoroethanol and triphos-derivatives.