CO2 Hydrogenation to Formate and Methanol as an Alternative to Photo- and Electrochemical CO2 Reduction

Tuning structures and catalysis performance of two-dimensional covalent organic frameworks based on copper phthalocyanine building block and phenyl connector

Based on the experimentally reported stable and conductive two-dimensional covalent organic frameworks with copper phthalocyanine (CuPc) as building block and cyan substituted phenyl as connector (CuCOF-CN) as an electrocatalyst for CO2 reduction reaction (RR), first principle calculations were performed on CuCOF-CN and its analog with the CN being replaced by H (CuCOF). Comparatively studied on the crystal structures, electronic properties, and CO2RR performance of the two catalysts found that CuCOF has reduced crystal unit size, more positive charge on Cu and CuPc segments, smaller band gap, and lower reaction barrier for CO2 RR than CuCOF-CN. CuCOF is proposed to be good potential electrocatalyst with good environment friendliness. The substituent effect and structure-property-performance relationship would help for designing and fabricating new electrocatalysts.

Universal synthesis of pure-phase IB-group Sn-based alloys with modulable electrocatalytic CO2 reduction products

We present a universal preparation method for synthesizing a range of pure-phase IB-group Sn-based alloy catalysts (Cu3Sn, Ag4Sn, and AuSn) for electrochemical reduction of CO2 to C1 product. The selectivity can be widely adjusted by altering metal composition and potential, improving the understanding of the structure-activity relationship in various Sn-based alloys.

Neutral mononuclear indium(III) photosensitizers for CO2 photoreduction

Herein, neutral mononuclear indium(III) complexes (In-1-In-3) containing 2,6-di(1H-pyrrol-2-yl)pyridine and substituted dipyridylpyrrole pincer ligand were employed as photosensitizers (PS) in photocatalytic CO2 reduction. In-2 exhibits good photo-activity and selectivity, which is superior to the classic PS Ru(bpy)32+. The amount of CO generation is 28.4 μmol with a CO selectivity of 93% when using In-2 as a PS and CoPc as a catalyst in CH3CN media.

Reaching machine learning leverage to advance performance of electrocatalytic CO2 conversion in non-aqueous deep eutectic electrolytes

Deep eutectic electrolytes (DEEs) show promise for future electrochemical systems due to their adjustable buffer capacities. This study utilizes machine learning algorithms to analyse the carbon dioxide reduction reaction (CO2RR) in DEEs with a buffer capacity of approximately 10.21 mol/pH. The objective is to minimize undesired hydrogen evolution reactions (HER) and render CO2RR dominant in a membrane cell. The CO2RR process was found to be non-adiabatic, as the time of nuclear motion for CO32- in K2CO3 product, through CO2●- trapping, is 0.368 femtoseconds shorter than the 1.856 × 10-3s charge transfer relaxation time. Microkinetic analysis reveals that the rate of CO2RR to CO2●- is 2.14 × 103 mol/cm2/s2 with a rate constant of 2.1 × 1010 cm/s. Our findings demonstrate that ensemble and k-Nearest Neighbours algorithms learn the CO2RR dataset, achieving a prediction accuracy of over 99%. The models were verified visually and quantitatively by overlaying predicted and experimental dataset. Diagnostic and SHAP analyses highlighted the gradient boost ensemble algorithm, predicting asymptotic current densities of -4.114 mA/cm2 or -13.340 mA/cm2, with high turnover frequencies (TOF) of 3.79 × 1010 h-1 or 12.30 × 1010 h-1 for CO2●- or K2CO3 generation on silver electrodes, respectively. These results consider both accuracy and robustness against overfitting, providing an opportunity to optimize future non-aqueous electrolytes for convenient TOF measurements at industrially relevant current densities.

Kinetic Studies of CO2 Insertion into Metal-Element σ-Bonds

ConspectusDespite the plethora of metal catalyzed reactions for CO2 utilization that have been developed in academic laboratories, practical systems remain elusive. The understanding of the elementary steps in catalysis is a proven method to improve catalytic performance. In many catalytic cycles for CO2 utilization, the insertion of CO2 into a metal-element σ-bond, such as hydrides, alkyls, amides, or hydroxides, is a crucial step. However, despite the many demonstrations of CO2 insertion, there are a paucity of kinetic studies, and information about the reaction mechanism has been predominantly elucidated from computational investigations. In this Account, kinetic studies on CO2 insertion into late transition metal-element σ-bonds performed by my group are summarized, along with their implications for catalysis.A common pathway for CO2 insertion into a metal hydride involves a two-step mechanism. The first step is nucleophilic attack on CO2 by the hydride to generate an H-bound formate, followed by rearrangement to form an O-bound formate product. Kinetic studies on systems in which both the first and second steps are proposed to be rate-determining, known as inner-sphere and outer-sphere processes, respectively, show that insertion rates increase as (i) the ligand trans to the hydride becomes a stronger donor, (ii) the ancillary ligand becomes more electron-donating, and (iii) the Dimroth-Reichardt parameter of the solvent increases. However, the magnitude of these effects is generally smaller for inner-sphere processes because there is less buildup of charge in the key transition state. For similar reasons, the presence of Lewis acids only increases the rate of outer-sphere processes. These results suggest it may be possible to experimentally differentiate between inner- and outer-sphere processes.The insertion of CO2 into a metal-alkyl bond results in the formation of a C-C bond, which is important for the generation of fuels from CO2. For square planar Group 10 complexes, the presence of a strong donor ligand trans to the alkyl group is critical for kinetically promoting insertion. Further, the nucleophilicity of the alkyl ligand directly impacts the rate of CO2 insertion via an SE2 mechanism, as does the steric bulk of the complex, and the reaction solvent. In contrast to the relatively slow rates of insertion observed for metal alkyls, CO2 insertion is rapid for metal hydroxides and amides. Although kinetics trends could be determined for hydroxides, reactions with amides are too fast for quantitative studies.Overall, the rates of insertion correlate with the nucleophilicity of the element in the metal-element σ-bond, so amide > hydroxide > hydride > alkyl. Due to the related pathways for insertion, similar trends in ligand and solvent effects are observed for insertion into different metal-element σ-bonds. Thus, the same strategies can be used to control the rates of insertion across systems. Differences in the magnitude of solvent and ligand effects are caused by variation in the amount of charge build-up on the metal in the rate-determining transition state. Likely, given that CO2 is related to organic molecules such as aldehydes, ketones, and amides, the results described in this Account are general to a wider range of substrates.

Toward Methanol Production by CO2 Hydrogenation beyond Formic Acid Formation

ConspectusThe Paradigm shift in considering CO2 as an alternative carbon feedstock as opposed to a waste product has recently prompted intense research activities. The implementation of CO2 utilization may be achieved by designing highly efficient catalysts, exploring processes that minimize energy consumption and simplifying product purification and separation. Among possible target products derived from CO2, methanol is highly valuable because it can be used in various chemical feedstocks and as a fuel. Although it is currently produced on a plant scale by heterogeneous catalysis using a Cu/ZnO-based catalyst, a limited theoretical conversion ratio at high reaction temperatures remains an issue. In addition, a catalytic system that can be adjusted to accommodate a variable renewable energy source for the synthesis of methanol is more desirable than current continuous-operation systems, which require a reliable energy supply. Recently, significant progress has been made in the field of homogeneous catalysis, which primarily relies on an indirect route to synthesize methanol via the hydrogenation of carbonate or formate derivatives in the presence of additives and solvents. However, homogeneous catalysis is inappropriate for industrial-scale methanol production because of the inefficient separation and purification processes involved.In this Account, we demonstrate a novel approach for methanol production under mild reaction conditions by CO2 hydrogenation catalyzed by multinuclear iridium complexes under heterogeneous gas-solid phase conditions without any additives and solvents. One of the aims of this Account provides insights for overcoming the barriers for efficient CO2 hydrogenation by focusing on catalyst design, specifically by incorporating varying functionalities into the ligand. The fundamental strategy entails activating hydrogen molecule and enhancing the hydricity of the resulting metal-hydride species, which is based on the following two concepts of catalyst design: (i) Activating a metal-hydride by electronic effects; and (ii) accelerating H2 heterolysis. We have elucidated the mechanism for accelerating H2 heterolysis using a state-of-the-art catalyst that contains an actor-ligand that responds to or participates in catalysis as opposed to a classical spectator-ligand.We have also demonstrated a novel heterogeneous catalysis using a molecular catalyst as a key step for the hydrogenation of CO2 to methanol beyond formic acid formation. The dehydrogenation of formic acid as a reverse reaction of formic acid hydrogenation is strongly favored in acidic aqueous solution. To circumvent the equilibrium limitation, we have envisioned an alternative route that both prevents the liberation of formic acid into the reaction medium, and develops a multinuclear complex to facilitate the transfer of multiple reactive hydrides. The unconventional gas-solid phase catalysis is capable of preventing the liberation of formate species and promoting further hydrogenation of formic acid through multihydride transfer.This novel catalytic system, which is the fusion of a molecular catalyst in heterogeneous catalysis, provides high performance for methanol synthesis through a sophisticated catalyst design and straightforward separation processes. A detailed mechanistic analysis of molecular catalysts in the gas phase would lead to significant progress in the field of Surface Organometallic Chemistry (SOMC).

A Data-Driven Approach for Enhanced CO2 Capture with Ruthenium Complexes

To attain carbon neutrality, significant efforts have been made to capture and utilize CO2. The homogeneous hydrogenation of CO2 catalyzed by transition metal complexes, particularly the ruthenium complexes, has demonstrated significant advantages and is regarded as a viable approach for practical application. Insertion of CO2 into the Ru-H bond, producing the Ru-formate product, is the key step in the hydrogenation of CO2. In order to parameterize the catalytic activities in the CO2 insertion into the Ru-H bond, the concept of simplified mechanism-based approach with data-driven practice (SMADP) has been introduced in this paper. The results showed that the hydricity of the Ru-H complex (ΔGH-) might serve as a single active descriptor in the process of CO2 insertion, and that a novel ruthenium complex in CO2 catalysis may not be easily obtained by mere modification of the auxiliary ligand at the ruthenium metal site.

Transition metal pincer catalysts for formic acid dehydrogenation: a mechanistic perspective

The storage and transportation of hydrogen gas, a non-polluting alternative to carbon-based fuels, have always been challenging due to its extreme flammability. In this regard, formic acid (FA) is a promising liquid organic hydrogen carrier (LOHC), and over the past decades, significant progress has been made in dehydrogenating FA through transition metal catalysis. In this review, our goal is to provide a detailed insight into the existing processes to expose various mechanistic challenges associated with FA dehydrogenation (FAD). Specifically, methodologies catalyzed by pincer-ligated metal complexes were chosen. Pincer ligands are preferred as they provide structural rigidity to the complexes, making the isolation and analysis of reaction intermediates less challenging and consequently providing a better mechanistic understanding. In this perspective, the catalytic activity of the reported pincer complexes in FAD was overviewed, and more importantly, the catalytic cycles were examined in detail. Further attention was given to the structural modifications, role of additives, reaction medium, and their crucial effects on the outcome.

First-Principles Insights into the Mechanism of CO2 Hydrogenation Reactions by Fe-PNP Pincer Complex

Using the state of the art theoretical methods, we have provided a comprehensive mechanistic understanding of the CO2 hydrogenation into HCOOH, H2CO, and CH3OH by 2,6-bis(diisopropylphosphinomethyl)pyridine (PNP)-ligated Fe pincer complex, featuring one CO and two H as co-ligands. For the computational investigation, a verified structural model containing methyl groups in place of the experimental isopropyl groups was used. Three catalytic conversions involving hydrogenation of CO2 into formic acid (HCOOH), HCOOH into formaldehyde and methanol were studied in different solvent medium. Our modelled complex appears to be a viable base-free catalyst for the conversion of CO2 into HCOOH and HCOOH into H2CO, based on the free energy profiles, which show apparent activation energy barriers of 16.28 kcal/mol and 23.63 kcal/mol for the CO2 to HCOOH and HCOOH to H2CO conversion, respectively. However, the computed results show that, due to the huge energy span of H2CO to CH3OH conversion, complete hydrogenation of CO2 into methanol could not occur under moderate conditions. Morpholine co-catalyst, which can lower the hydrogenation barrier by taking part in a simultaneous H-atom donation-acceptance process, could have assisted in completing this step.

Four-electron reduction of CO2: from formaldehyde and acetal synthesis to complex transformations

The expansive and dynamic field of the CO2 Reduction Reaction (CO2RR) seeks to harness CO2 as a sustainable carbon source or energy carrier. While significant progress has been made in two, six, and eight-electron reductions of CO2, the four-electron reduction remains understudied. This review fills this gap, comprehensively exploring CO2 reduction into formaldehyde (HCHO) or acetal-type compounds (EOCH2OE, with E = [Si], [B], [Zr], [U], [Y], [Nb], [Ta] or -R) using various CO2RR systems. These encompass (photo)electro-, bio-, and thermal reduction processes with diverse reductants. Formaldehyde, a versatile C1 product, is challenging to synthesize and isolate from the CO2RR. The review also discusses acetal compounds, emphasizing their significance as pathways to formaldehyde with distinct reactivity. Providing an overview of the state of four-electron CO2 reduction, this review highlights achievements, challenges, and the potential of the produced compounds - formaldehyde and acetals - as sustainable sources for valuable product synthesis, including chiral compounds.

CuO (111) Microcrystalline Evoked Indium-Organic Framework for Efficient Electroreduction of CO2 to Formate

Electrochemical reduction of carbon dioxide (CO2RR) to formate is economically beneficial but suffers from poor selectivity and high overpotential. Herein, enriched microcrystalline copper oxide is introduced on the surface of indium-based metal-organic frameworks. Benefiting from the CuO (111) microcrystalline shell and formed catalytic active In-Cu interfaces, the obtained MIL-68(In)/CuO heterostructure display excellent CO2RR to formate with a Faradaic efficiency (FE) as high as 89.7% at low potential of only -0.7 V vs. RHE in a flow cell. Significantly, the membrane electrode assembly (MEA) cell based on MIL-68(In)/CuO exhibit a remarkable current density of 640.3 mA cm-2 at 3.1 V and can be stably operated for 180 h at 2.7 V with a current density of 200 mA cm-2. The ex/in situ electrochemical investigations reveal that the introduction of CuO increases the formation rate of the carbon dioxide reduction intermediate *HCOO- and inhibits the competitive hydrogen evolution reaction. This work not only provides an in-depth study of the mechanism of the CO2RR pathways on In/Cu composite catalyst but also offers an effective strategy for the interface design of electrocatalytic carbon dioxide reduction reaction.

Conversion of Carbon Dioxide into a Series of CBxOy- Compounds Mediated by LaB3,4O2- Anions: Synergy of the Electron Transfer and Lewis Pair Mechanisms to Construct B-C Bonds

Converting CO2 into value-added products containing B-C bonds is a great challenge, especially for multiple B-C bonds, which are versatile building blocks for organoborane chemistry. In the condensed phase, the B-C bond is typically formed through transition metal-catalyzed direct borylation of hydrocarbons via C-H bond activation or transition metal-catalyzed insertion of carbenes into B-H bonds. However, excessive amounts of powerful boryl reagents are required, and products containing B-C bonds are complex. Herein, a novel method to construct multiple B-C bonds at room temperature is proposed by the gas-phase reactions of CO2 with LaBmOn- (m = 1-4, n = 1 or 2). Mass spectrometry and density functional theory calculations are applied to investigate these reactions, and a series of new compounds, CB2O2-, CB3O3-, and CB3O2-, which possess B-C bonds, are generated in the reactions of LaB3,4O2- with CO2. When the number of B atoms in the clusters is reduced to 2 or 1, there is only CO-releasing channel, and no CBxOy- compounds are released. Two major factors are responsible for this quite intriguing reactivity: (1) Synergy of electron transfer and boron-boron Lewis acid-base pair mechanisms facilitates the rupture of C═O double bond in CO2. (2) The boron sites in the clusters can efficiently capture the newly formed CO units in the course of reactions, favoring the formation of B-C bonds. This finding may provide fundamental insights into the CO2 transformation driven by clusters containing lanthanide atoms and how to efficiently build B-C bonds under room temperature.

Heterogeneous Photocatalytic C(sp2)-H Activation of Formate for Hydrocarboxylation of Alkenes

Light-driven carboxylation offers a promising approach for synthesizing valuable fine chemicals under mild conditions. Here we disclose a heterogeneous photocatalytic strategy of C(sp2)-H activation of formate for hydrocarboxylation of alkenes over zinc indium sulfide (ZnIn2S4) under visible light. This protocol functions well with a variety of substituted styrenes with good to excellent yields; it also works for unactivated alkenes albeit with lower yields. Mechanistic studies confirm the existence of CO2⋅- as a key intermediate. It was found that C(sp2)-H activation of formate is induced by S⋅ species on the surface of ZnIn2S4 via hydrogen atom transfer (HAT) instead of a photogenerated hole oxidation mechanism. Moreover, both cleavage of the C(sp2)-H of HCOO- and formation of a benzylic anion were found to be involved in the rate-determining step for the hydrocarboxylation of styrene.

Redirecting electron flow in Acetobacterium woodii enables growth on CO and improves growth on formate

Anaerobic, acetogenic bacteria are well known for their ability to convert various one-carbon compounds, promising feedstocks for a future, sustainable biotechnology, to products such as acetate and biofuels. The model acetogen Acetobacterium woodii can grow on CO2, formate or methanol, but not on carbon monoxide, an important industrial waste product. Since hydrogenases are targets of CO inhibition, here, we genetically delete the two [FeFe] hydrogenases HydA2 and HydBA in A. woodii. We show that the ∆hydBA/hydA2 mutant indeed grows on CO and produces acetate, but only after a long adaptation period. SNP analyzes of CO-adapted cells reveal a mutation in the HycB2 subunit of the HydA2/HydB2/HydB3/Fdh-containing hydrogen-dependent CO2 reductase (HDCR). We observe an increase in ferredoxin-dependent CO2 reduction and vice versa by the HDCR in the absence of the HydA2 module and speculate that this is caused by the mutation in HycB2. In addition, the CO-adapted ∆hydBA/hydA2 mutant growing on formate has a final biomass twice of that of the wild type.

Detection and Characterization of Hydride Ligands in Copper Complexes by Hard X-Ray Spectroscopy

Transition metal complexes, particularly copper hydrides, play an important role in various catalytic processes and molecular inorganic chemistry. This study employs synchrotron hard X-ray spectroscopy to gain insights into the geometric and electronic properties of copper hydrides as potential catalysts for CO2 hydrogenation. The potential of high energy resolution X-ray absorption near-edge structure (HERFD-XANES) and valence-to-core X-ray emission (VtC-XES) is demonstrated with measurement on Stryker's reagent (Cu6H6) and [Cu3(μ3-H)(dpmppe)2](PF6)2 (Cu3H), alongside a non-hydride copper compound ICu(dtbppOH) (Cuy-I). The XANES analysis reveals that coordination geometries strongly influence the spectra, providing only indirect details about hydride coordination. The VtC-XES analysis exhibits a distinct signal around 8975 eV, offering a diagnostic tool to identify hydride ligands. Theoretical calculations support and extend these findings by comparing hydride-containing complexes with their hydride-free counterparts.

Development of ruthenium complexes with S-donor ligands for application in synthesis, catalytic acceptorless alcohol dehydrogenation and crossed-aldol condensation

The reaction of [Ru(dmso)4Cl2] with a potassium salt of four xanthate (RO-C(S)S-; R = Me, Et, iPr and tBu) ligands (depicted as Ln; n = 1-4) in hot methanol afforded a group of mixed-ligand complexes of type [Ru(Ln)2(dmso)2]. The crystal structures of all the four complexes have been determined, which show that the xanthate ligands are bound to the metal center forming four-membered chelates and dmso is coordinated through sulfur and they are mutually cis. The relative thermodynamic stability of this cis and the other possible trans-isomers of these complexes has been assessed with the help of DFT calculations, which have revealed that the cis-isomer is the more stable isomer. The coordinated dmso in the [Ru(Ln)2(dmso)2] complexes could be easily displaced by chelating bidentate ligands (depicted as L') to furnish complexes of type [Ru(Ln)2(L')], as demonstrated through isolation of two such complexes, viz. [Ru(L3)2(bpy)] and [Ru(L2)2(phen)] (bpy = 2,2'-bipyridine and phen = 1,10-phenanthroline). The crystal structure of [Ru(L3)2(bpy)] has been determined and the structure of [Ru(L2)2(phen)] has been optimized by the DFT method. The electronic spectra of the four [Ru(Ln)2(dmso)2] complexes and the two derivatives ([Ru(Ln)2(L')]; n = 3, L' = bpy; n = 2, L' = phen), recorded in dichloromethane solutions, show intense absorptions spanning the visible and ultraviolet regions, which have been analyzed by the TDDFT method. The [Ru(Ln)2(dmso)2] complexes are found to serve as efficient catalyst precursors for the acceptorless dehydrogenation of 2-propanol followed by crossed-aldol condensation with substituted benzaldehydes (and related aldehydes), using tert-butoxide as the co-catalyst, producing dibenzylideneacetone derivatives in good yields.

Molybdenum-catalyzed hydrogenation of carbon dioxide, bicarbonate, and inorganic carbonates to formates

Herein, we report the hydrogenation of carbon dioxide to sodium formate catalyzed by low-valent molybdenum phosphine complexes. The 1,3-bis(diphenylphosphino)propane (DPPP)-based Mo complex was found to be an efficient catalyst in the presence of NaOH affording formate with a TON of 975 at 130 °C in THF/H2O after 24 h utilizing 40 bar (CO2 : H2 = 10 : 30) pressure. The complex was also active in the hydrogenation of sodium bicarbonate and inorganic carbonates to the corresponding formates. Mechanistic investigation revealed that the reaction proceeded via an intermediate formato complex.

Engineering Frustrated Lewis Pair Active Sites in Porous Organic Scaffolds for Catalytic CO2 Hydrogenation

Frustrated Lewis pairs (FLPs), featuring reactive combinations of Lewis acids and Lewis bases, have been utilized for myriad metal-free homogeneous catalytic processes. Immobilizing the active Lewis sites to a solid support, especially to porous scaffolds, has shown great potential to ameliorate FLP catalysis by circumventing some of its inherent drawbacks, such as poor product separation and catalyst recyclability. Nevertheless, designing immobilized Lewis pair active sites (LPASs) is challenging due to the requirement of placing the donor and acceptor centers in appropriate geometric arrangements while maintaining the necessary chemical environment to perform catalysis, and clear design rules have not yet been established. In this work, we formulate simple guidelines to build highly active LPASs for direct catalytic hydrogenation of CO2 through a large-scale screening of a diverse library of 25,000 immobilized FLPs. The library is built by introducing boron-containing acidic sites in the vicinity of the existing basic nitrogen sites of the organic linkers of metal-organic frameworks collected in a "top-down" fashion from the CoRE MOF 2019 database. The chemical and geometrical appropriateness of these LPASs for CO2 hydrogenation is determined by evaluating a series of simple descriptors representing the intrinsic strength (acidity and basicity) of the components and their spatial arrangement in the active sites. Analysis of the leading candidates enables the formulation of pragmatic and experimentally relevant design principles which constitute the starting point for further exploration of FLP-based catalysts for the reduction of CO2.

Skeletal Formation of Carbocycles with CO2: Selective Synthesis of Indolo[3,2-b]carbazoles or Cyclophanes from Indoles, CO2, and Phenylsilane

The catalytic reactions of indoles with CO2 and phenylsilane afforded indolo[3,2-b]carbazoles, where the fused benzene ring was constructed by forming two C-H bonds and four C-C bonds with two CO2 molecules via deoxygenative conversions. Nine-membered cyclophanes made up of three indoles and three CO2 molecules were also obtained, where the cyclophane framework was constructed by forming six C-H bonds and six C-C bonds. These multicomponent cascade reactions giving completely different carbocycles were switched simply by choosing the solvent, acetonitrile or ethyl acetate.

Atomic/molecular layer deposition strategies for enhanced CO2 capture, utilisation and storage materials

Elevated levels of carbon dioxide (CO2) in the atmosphere and the diminishing reserves of fossil fuels have raised profound concerns regarding the resulting consequences of global climate change and the future supply of energy. Hence, the reduction and transformation of CO2 not only mitigates environmental pollution but also generates value-added chemicals, providing a dual remedy to address both energy and environmental challenges. Despite notable advancements, the low conversion efficiency of CO2 remains a major obstacle, largely attributed to its inert chemical nature. It is imperative to engineer catalysts/materials that exhibit high conversion efficiency, selectivity, and stability for CO2 transformation. With unparalleled precision at the atomic level, atomic layer deposition (ALD) and molecular layer deposition (MLD) methods utilize various strategies, including ultrathin modification, overcoating, interlayer coating, area-selective deposition, template-assisted deposition, and sacrificial-layer-assisted deposition, to synthesize numerous novel metal-based materials with diverse structures. These materials, functioning as active materials, passive materials or modifiers, have contributed to the enhancement of catalytic activity, selectivity, and stability, effectively addressing the challenges linked to CO2 transformation. Herein, this review focuses on ALD and MLD's role in fabricating materials for electro-, photo-, photoelectro-, and thermal catalytic CO2 reduction, CO2 capture and separation, and electrochemical CO2 sensing. Significant emphasis is dedicated to the ALD and MLD designed materials, their crucial role in enhancing performance, and exploring the relationship between their structures and catalytic activities for CO2 transformation. Finally, this comprehensive review presents the summary, challenges and prospects for ALD and MLD-designed materials for CO2 transformation.

CO2 reduction using aluminum hydride: Generation of in-situ frustrated Lewis pairs and small molecule activation therein

CO2 reduction is appealing for the long-term production of high-value fuels and chemicals. Herein, using density functional theory (DFT) based calculations, we study the CO2 reduction pathway to formic acid using aluminum hydride and phosphine derivatives. Our primary focus is on aluminum hydride derivatives, aimed at improving the efficiency of the CO2 reduction process. Substituents with σ-donating properties at the aluminum center are discovered to lower the activation barriers. We demonstrate how di-tert-butylphosphine oxide (LB-O)/di-tert-butylphosphine sulfide (LB-S)/di-tert-butylphosphanimine (LB-N) work together with aluminum hydride to facilitate CO2 reduction process and generate in-situ frustrated Lewis pairs (FLPs), such as FLP-O, FLP-S, and FLP-N. The activation strain model (ASM) analysis reveals the significance of strain energy in determining activation barriers. EDA-NOCV and PIO analyses elucidate the orbital interactions at the corresponding transition states. Furthermore, the study delves into the activation of various small molecules, such as dihydrogen, acetylene, ethylene, carbon dioxide, nitrous oxide, and acetonitrile, using those in-situ generated FLPs. The study highlights the low activation barriers and emphasizes the potential for small molecule activation in this context.

Influence of water chemistry and operating parameters on PFOS/PFOA removal using rGO-nZVI nanohybrid

Graphene and zero-valent-iron based nanohybrid (rGO-nZVI NH) with oxidant H2O2 can remove perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) through adsorption-degradation in a controlled aquatic environment. In this study, we evaluated how and to what extent different environmental and operational parameters, such as initial PFAS concentration, H2O2 dose, pH, ionic strength, and natural organic matter (NOM), influenced the removal of PFOS and PFOA by rGO-nZVI. With the increase in initial PFAS concentration (from 0.4 to 50 ppm), pH (3 to 9), ionic strength (0 to 100 mM), and NOM (0 to 10 ppm), PFOS removal reduced by 20%, 30%, 2%, and 6%, respectively, while PFOA removal reduced by 54%, 76%, 11%, and 33% respectively. In contrast, PFOS and PFOA removal increased by 10% and 41%, respectively, with the increase in H2O2 (from 0 to 1 mM). Overall, the effect of changes in environmental and operational parameters was more pronounced for PFOA than PFOS. Mechanistically, •OH radical generation and availability showed a profound effect on PFOA removal. Also, the electrostatic interaction between rGO-nZVI NH and deprotonated PFAS compounds was another key factor for removal. Most importantly, our study confirms that rGO-nZVI in the presence of H2O2 can degrade both PFOS and PFOA to some extent by identifying the important by-products such as acetate, formate, and fluoride.

Electrocatalytic CO2 reduction to formate by a cobalt phosphino-thiolate complex

Electrochemical conversion of CO2 to value-added products serves as an attractive method to store renewable energy as energy-dense fuels. Selectivity in this type of conversion can be limited, often leading to the formation of side products such as H2. The activity of a cobalt phosphino-thiolate complex ([Co(triphos)(bdt)]+) towards the selective reduction of CO2 to formate is explored in this report. In the presence of H2O, selective production of formate (as high as 94%) is observed at overpotentials of 750 mV, displaying negligible current degradation during long-term electrolysis experiments ranging as long as 24 hours. Chemical reduction studies of [Co(triphos)(bdt)]+ indicates deligation of the apical phosphine moiety is likely before catalysis. Computational and experimental results suggest a metal-hydride pathway, indicating an ECEC based mechanism.

Ligand-Dominated Activation of CO2 and CS2 by the Putative Nickel Phosphiniminato Intermediates

Room-temperature photoactivation of the first- and second-generation PN3P-pincer nickel azido complexes 1a and 1b in the presence of CO2 or CS2 afforded N-bound carbamates, dithiocarbamates, and isothiocyanates, providing insights into CO2 and CS2 activation and demonstrating how a seemingly small difference in the ligand structure significantly influences the reactivity. Theoretical calculations disclosed that the charge of the phosphorus atom plays a critical role in determining the nitrogen atom transfer to form a plausible nickel phosphiniminato intermediate.

Local CO2 reservoir layer promotes rapid and selective electrochemical CO2 reduction

Electrochemical CO2 reduction reaction in aqueous electrolytes is a promising route to produce added-value chemicals and decrease carbon emissions. However, even in Gas-Diffusion Electrode devices, low aqueous CO2 solubility limits catalysis rate and selectivity. Here, we demonstrate that when assembled over a heterogeneous electrocatalyst, a film of nitrile-modified Metal-Organic Framework (MOF) acts as a remarkable CO2-solvation layer that increases its local concentration by ~27-fold compared to bulk electrolyte, reaching 0.82 M. When mounted on a Bi catalyst in a Gas Diffusion Electrode, the MOF drastically improves CO2-to-HCOOH conversion, reaching above 90% selectivity and partial HCOOH currents of 166 mA/cm2 (at -0.9 V vs RHE). The MOF also facilitates catalysis through stabilization of reaction intermediates, as identified by operando infrared spectroscopy and Density Functional Theory. Hence, the presented strategy provides new molecular means to enhance heterogeneous electrochemical CO2 reduction reaction, leading it closer to the requirements for practical implementation.

Photocatalytic CO2 Reduction Using CO2-Binding Enzymes

Novel concepts to utilize carbon dioxide are required to reach a circular carbon economy and minimize environmental issues. To achieve these goals, photo-, electro-, thermal-, and biocatalysis are key tools to realize this, preferentially in aqueous solutions. Nevertheless, catalytic systems that operate efficiently in water are scarce. Here, we present a general strategy for the identification of enzymes suitable for CO2 reduction based on structural analysis for potential carbon dioxide binding sites and subsequent mutations. We discovered that the phenolic acid decarboxylase from Bacillus subtilis (BsPAD) promotes the aqueous photocatalytic CO2 reduction selectively to carbon monoxide in the presence of a ruthenium photosensitizer and sodium ascorbate. With engineered variants of BsPAD, TONs of up to 978 and selectivities of up to 93 % (favoring the desired CO over H2 generation) were achieved. Mutating the active site region of BsPAD further improved turnover numbers for CO generation. This also revealed that electron transfer is rate-limiting and occurs via multistep tunneling. The generality of this approach was proven by using eight other enzymes, all showing the desired activity underlining that a range of proteins is capable of photocatalytic CO2 reduction.

Carbon dioxide capture and functionalization by bis(N-heterocyclic carbene)-borylene complexes

Derivatives of free monocoordinated borylenes have attracted considerable interest due to their ability to exhibit transition-metal-like reactivity, in particular small molecules capture. However, such complexes are rare as the formation is either endergonic, or the resulting adduct is a transient intermediate that is prone to reaction. Here, we present the synthesis of two bis(N-heterocyclic carbene)-borylene complexes capable of capturing and functionalizing carbon dioxide. The capture and subsequent functionalization of CO2 by the bis(NHC)-disilylamidoborylene 1 is demonstrated by the formation of the bis(NHC)-isocyanatoborylene-carbon dioxide complex 3. Reversible capture of CO2 is observed using the bis(NHC)-mesitylborylene 2, and the persistent bis(NHC)-mesitylborylene-carbon dioxide adduct 4 can be stabilized by hydrogen bonding with boric acid. The reactions of 4 with ammonia-borane and aniline demonstrate that the captured CO2 can be further functionalized.

Formoxyboranes as hydroborane surrogates for the catalytic reduction of carbonyls through transfer hydroboration

A new class of Lewis base stabilized formoxyboranes demonstrates the feasibility of catalytic transfer hydroboration. In the presence of a ruthenium catalyst, they have shown broad applicability for reducing carbonyl compounds. Various borylated alcohols are obtained in high selectivity and yields up to 99%, tolerating several functional groups. Computational studies enabled to propose a mechanism for this transformation, revealing the role of the ruthenium catalyst and the absence of hydroborane intermediates.

Effect of Alkali- and Alkaline-Earth-Metal Promoters on Silica-Supported Co-Fe Alloy for Autocatalytic CO2 Fixation

Hydrothermal vents harbor numerous microbial communities rich in reduced carbon species such as formate, acetate, and hydrocarbons. Such essential chemicals for life are produced by H2 -dependent CO2 reduction, where serpentinization provides continuous H2 and thermal energy. Here, we show that silica-supported bimetallic Co-Fe alloys, naturally occurring minerals around serpentinite, can convert CO2 and H2 O to key metabolic intermediates of the acetyl coenzyme A pathway such as formate (up to 72 mM), acetate, and pyruvate under mild hydrothermal vent conditions. Long-chain hydrocarbons up to C6 including propene are also detected, just as in the Lost City hydrothermal field. The effects of promoters on structural properties and catalytic functionalities of the Co-Fe alloy are systematically investigated by incorporating a series of alkali and alkaline earth metals including Na, Mg, K, and Ca. Alkali and alkaline earth metals resulted in higher formate concentrations when dissolved in water and increased reaction pH, while alkaline earth metals also favored the formation of insoluble hydroxides and carbonates similar to the constituent minerals of the chimneys at the Lost City hydrothermal fields.

Cyclopentadienone Diphosphine Ruthenium Complex: A Designed Catalyst for the Hydrogenation of Carbon Dioxide to Methanol

The development of homogeneous metal catalysts for the efficient hydrogenation of carbon dioxide (CO2) into methanol (CH3OH) remains a significant challenge. In this study, a new cyclopentadienone diphosphine ligand (CPDDP ligand) was designed, which could coordinate with ruthenium to form a Ru-CPDDP complex to efficiently catalyze the CO2-to-methanol process using dihydrogen (H2) as the hydrogen resource based on density functional theory (DFT) mechanistic investigation. This process consists of three catalytic cycles, stage I (the hydrogenation of CO2 to HCOOH), stage II (the hydrogenation of HCOOH to HCHO), and stage III (the hydrogenation of HCHO to CH3OH). The calculated free energy barriers for the hydrogen transfer (HT) steps of stage I, stage II, and stage III are 7.5, 14.5, and 3.5 kcal/mol, respectively. The most favorable pathway of the dihydrogen activation (DA) steps of three stages to regenerate catalytic species is proposed to be the formate-assisted DA step with a free energy barrier of 10.4 kcal/mol. The calculated results indicate that the designed Ru-CPDDP and Ru-CPDDPEt complexes could catalyze hydrogenation of CO2 to CH3OH (HCM) under mild conditions and that the transition-metal owning designed CPDDP ligand framework be one kind of promising potential efficient catalysts for HCM.

Formic acid stability in different solvents by DFT calculations

CONTEXT

New technologies have been developed toward the use of green energies. The production of formic acid (FA) from carbon dioxide (CO[Formula: see text]) hydrogenation with H[Formula: see text] is a sustainable process for H[Formula: see text] storage. However, the FA adduct stabilization is thermodynamically dependent on the type of solvent and thermodynamic conditions. The results suggest a wide range of dielectric permittivity values between the dimethyl sulfoxide (DMSO) and water solvents to stabilize the FA in the absence of base. The thermodynamics analysis and the infrared and charge density difference results show that the formation of the FA complex with H[Formula: see text]O is temperature dependent and has a major influence on aqueous solvents compared to the FA adduct with amine, in good agreement with the experiment. In these conditions, the stability thermodynamic of the FA molecule may be favorable at non-organic solvents and dielectric permittivity values closer to water. Therefore, a mixture of aqueous solvents with possible ionic composition could be used to increase the thermodynamic stability of H[Formula: see text] storage in CO[Formula: see text] conversion processes.

METHODS

Using the Quantum ESPRESSO package, density functional theory (DFT) calculations were performed with periodic boundary conditions, and the electronic wave functions were expanded in plane waves. For the exchange-correlation functional, we use the vdW-DF functional with the inclusion of van der Waals (vdW) forces. Electron-ion interactions are treated by the projector augmented wave (PAW) method with pseudopotentials available in the PSlibrary repository. The wave functions and the electronic densities were expanded employing accurate cut-off energies of 6.80[Formula: see text]10[Formula: see text] and 5.44[Formula: see text]10[Formula: see text] eV, respectively. The electronic density was computed from the wave functions calculated at the [Formula: see text]-point in the first Brillouin-zone. Each structural optimization was minimized according to the Broyden-Fletcher-Goldfarb-Shanno (BFGS) algorithm, with force and energy convergence criteria of 25 meV[Formula: see text]Å[Formula: see text] and 1.36 meV, respectively. The electrostatic solvation effects were performed by the [Formula: see text] package with the Self-Consistent Continuum Solvation (SCCS) approach.

Fundamentals and Recent Progress in Magnetic Field Assisted CO2 Capture and Conversion

CO2 capture and conversion technology are highly promising technologies that definitely play a part in the journey towards carbon neutrality. Releasing CO2 by mild stimulation and the development of high efficiency catalytic processes are urgently needed. The magnetic field, as a thermodynamic parameter independent of temperature and pressure, is vital in the enhancement of CO2 capture and conversion process. In this review, the recent progress of magnetic field-enhanced CO2 capture and conversion is comprehensively summarized. The theoretical fundamentals of magnetic field on CO2 adsorption, release and catalytic reduction process are discussed, including the magnetothermal, magnetohydrodynamic, spin selection, Lorentz forces, magnetoresistance and spin relaxation effects. Additionally, a thorough review of the current progress of the enhancement strategies of magnetic field coupled with a variety of fields (including thermal, electricity, and light) is summarized in the aspect of CO2 related process. Finally, the challenges and prospects associated with the utilization of magnetic field-assisted techniques in the construction of CO2 capture and conversion systems are proposed. This review offers a reference value for the future design of catalysts, mechanistic investigations, and practical implementation for magnetic field enhanced CO2 capture and conversion.

Isolation, Characterization and Reactivity of Key Intermediates Relevant to Reductive (Electro)catalysis with Cp*Rh Complexes Containing Pyridyl-MIC (MIC=Mesoionic Carbene) Ligands

In recent years, metal complexes of pyridyl-mesoionic carbene (MIC) ligands have been reported as excellent homogeneous and molecular electrocatalysts. In combination with group 9 metals, such ligands form highly active catalysts for hydrogenation/transfer hydrogenation/hydrosilylation catalysis and electrocatalysts for dihydrogen production. Despite such progress, very little is known about the structural/electrochemical/spectroscopic properties of crucial intermediates for such catalytic reactions with these ligands: solvato complexes, reduced complexes and hydridic species. We present here a comprehensive study involving the isolation, crystallographic characterization, electrochemical/spectroelectrochemical/theoretical investigations, and in-situ reactivity studies of all the aforementioned crucial intermediates involving Cp*Rh and pyridyl-MIC ligands. A detailed mechanistic study of the precatalytic activation of [RhCp*] complexes with pyridyl-MIC ligands is presented. Intriguingly, amphiphilicity of the [RhCp*]-hydride complexes was observed, displaying the substrate dependent transfer of H+ , H or H- . To the best of our knowledge, this study is the first of its kind targeting intermediates and reactive species involving metal complexes of pyridyl-MIC ligands and investigating the interconversion amongst them.

Thermochemical Properties of Synthesized Urea from Recovered Ammonia and Carbon Dioxide in Well-Ordered Nanospaces of Hollow Silica Spheres

The present work investigated the thermochemical properties of urea synthesized in well-ordered nanospaces of porous hollow silica spheres' shells from recovered ammonia and carbon dioxide in aqueous solution. Thermochemical behaviors of the urea synthesized in well-ordered nanospaces of the hollow spheres' shells prepared with 1-dodeclyamine were analyzed from the results of thermogravimetric analysis (TGA) and differential thermal analysis (DTA), and endothermic peaks assigned as the phase transition and decomposition were observed at ca. 440 and 514 K, respectively, which were higher than those of pristine urea (405 and 408 K, respectively), probably because of the nanoconfinement effect. The decomposition behavior was also confirmed by the result of diffuse reflectance infrared Fourier transform (DRIFT) spectra of the samples treated at various temperatures up to 573 K, and the decomposition of urea synthesized in the well-ordered nanospaces of the hollow spheres' shells started at 468 K and completed up to 533 K.

Contemporary advances in photocatalytic CO2 reduction using single-atom catalysts supported on carbon-based materials

The persistent issue of CO2 emissions and their subsequent impact on the Earth's atmosphere can be effectively addressed through the utilization of efficient photocatalysts. Employing a sustainable carbon cycle via photocatalysis presents a promising technology for simultaneously managing the greenhouse effect and the energy dilemma. However, the efficiency of energy conversion encounters limitations due to inadequate carrier utilization and a deficiency of reactive sites. Single-atom catalysts (SACs) have demonstrated exceptional performance in efficiently addressing the aforementioned challenges. This review article commences with an overview of SAC types, structures, fundamentals, synthesis strategies, and characterizations, providing a logical foundation for the design and properties of SACs based on the correlation between their structure and efficiency. Additionally, we delve into the general mechanism and the role of SACs in photocatalytic CO2 reduction. Furthermore, we furnish a comprehensive survey of the latest advancements in SACs concerning their capacity to enhance efficiency, long-term stability, and selectivity in CO2 reduction. Carbon-structured support materials such as covalent organic frameworks (COFs), graphitic carbon nitride (g-C3N4), metal-organic frameworks (MOFs), covalent triazine frameworks (CTFs), and graphene-based photocatalysts have garnered significant attention due to their substantial surface area, superior conductivity, and chemical stability. These carbon-based materials are frequently chosen as support matrices for anchoring single metal atoms, thereby enhancing catalytic activity and selectivity. The motivation behind this review article lies in evaluating recent developments in photocatalytic CO2 reduction employing SACs supported on carbon substrates. In conclusion, we highlight critical issues associated with SACs, potential prospects in photocatalytic CO2 reduction, and existing challenges. This review article is dedicated to providing a comprehensive and organized compilation of recent research findings on carbon support materials for SACs in photocatalytic CO2 reduction, with a specific focus on materials that are environmentally friendly, readily accessible, cost-effective, and exceptionally efficient. This work offers a critical assessment and serves as a systematic reference for the development of SACs supported on MOFs, COFs, g-C3N4, graphene, and CTFs support materials to enhance photocatalytic CO2 conversion.

Reductive Amination of Levulinic Acid to Pyrrolidones: Key Step in Biomass Valorization towards Nitrogen-Containing Chemicals

Nowadays, the field of biomass conversion is gradually moving towards an encouraging stage. The preparation of nitrogen-containing chemicals using various biomass resources instead of fossil resources do not only reduce carbon emissions, but also diversify the products of biomass conversion, thus increasing the economic competitiveness of biomass refining systems. Levulinic acid (LA) can be used as a promising intermediate in biomass conversion for further synthesis of pyrrolidone via reductive amination. However, there are still many critical issues to be solved. Particularly, the specific effects of catalysts on the performance of LA reductive amination have not been sufficiently revealed, and the potential impacts of key conditional factors have not been clearly elucidated. In view of this, this review attempts to provide theoretical insights through an in-depth interpretation of the above key issues. The contribution of catalysts to the reductive amination of LA as well as the catalyst structural preferences for improving catalytic performance are discussed. In addition, the role of key conditional factors is discussed. The insights presented in this review will contribute to the design of catalyst nanostructures and the rational configuration of green reaction conditions, which may provide inspiration to facilitate the nitrogen-related transformation of more biomass platform molecules.

Photocatalytic CO2 Reduction Coupled with Oxidation of Benzyl Alcohol over CsPbBr3@PANI Nanocomposites

Herein, we successfully prepare conductive polyaniline (PANI)-encapsulated CsPbBr3 perovskite nanocrystals (PNCs) that demonstrate much improved photocatalytic performance and stability toward the CO2 reduction reaction (CRR) coupled with oxidation of benzyl alcohol (BA) to benzaldehyde. Due to the acid-base interaction between CO2 and PANI, CO2 molecules are selectively adsorbed on PANI in the form of carbamate. As a result, the rate of production of CO (rCO) reaches 26.1 μmol g-1 h-1 with a selectivity of 98.1%, which is in good agreement with the rate of oxidation (∼27.0 μmol g-1 h-1) of BA. Such a high reduction/oxidation rate is enabled by the fast electron transfer (∼2.2 ps) from PNCs to PANI, as revealed by femtosecond transient absorption spectroscopy. Moreover, because of the benefit of the encapsulation of PANI, no significant decrease in rCO is observed in a 10 h CRR test. This work offers insight into how to simultaneously achieve improved photocatalytic performance and stability of CsPbX3 PNCs.

H2-driven reduction of CO2 to formate using bacterial plasma membranes

Bacterial membranes shield the intracellular compartment by selectively allowing unwanted substances to enter in, which in turn reduces overall catalytic efficiency. This report presents a model system using the isolated plasma membranes of Citrobacter sp. S-77 that harbor oxygen-stable [NiFe]hydrogenase and [Mo]formate dehydrogenase, which are integrated into a natural catalytic nanodevice through an electron transfer relay. This naturally occurring nanodevice exhibited selectivity and efficiency in catalyzing the H2-driven conversion of CO2 to formate with the rate of 817 mmol·L-1·gprotein-1·h-1 under mild conditions of 30 °C, pH 7.0, and 0.1 MPa. When the isolated plasma membranes of Citrobacter sp. S-77 was immobilized with multi-walled carbon nanotubes and encapsulated in hydrogel beads of gellan-gum cross-linked with calcium ions, the catalyst for formate production remained stable over 10 repeated uses. This paper reports the first case of efficient and selective formate production from H2 and CO2 using bacterial plasma membranes.

The role of metal accessibility on carbon dioxide electroreduction in atomically precise nanoclusters

Atomically precise nanoclusters (NCs) can be designed with high faradaic efficiency for the electrochemical reduction of CO2 to CO (FECO) and provide useful model systems for studying the metal-catalysed CO2 reduction reaction (CO2RR). While size-dependent trends are commonly evoked, the effect of NC size on catalytic activity is often convoluted by other factors such as changes to surface structure, ligand density, and electronic structure, which makes it challenging to establish rigorous structure-property relationships. Herein, we report a detailed investigation of a series of NCs [AunAg46-n(C[triple bond, length as m-dash]CR)24Cl4(PPh3)2, Au24Ag20(C[triple bond, length as m-dash]CR)24Cl2, and Au43(C[triple bond, length as m-dash]CR)20/Au42Ag1(C[triple bond, length as m-dash]CR)20] with similar sizes and core structures but different ligand packing densities to investigate how the number of accessible metal sites impacts CO2RR activity and selectivity. We develop a simple method to determine the number of CO2-accessible sites for a given NC then use this to probe relationships between surface accessibility and CO2RR performance for atomically precise NC catalysts. Specifically, the NCs with the highest number of accessible metal sites [Au43(C[triple bond, length as m-dash]CR)20 and Au42Ag1(C[triple bond, length as m-dash]CR)20] feature a FECO of >90% at -0.57 V vs. the reversible hydrogen electrode (RHE), while NCs with lower numbers of accessible metal sites have a reduced FECO. In addition, CO2RR studies performed on other Au-alkynyl NCs that span a wider range of sizes further support the relationship between FECO and the number of accessible metal sites, regardless of NC size. This work establishes a generalizable approach to evaluating the potential of atomically precise NCs for electrocatalysis.

Enhanced Electrocatalytic CO2 Reduction Reactivity of S- and N-Doped Fe-Embedded Graphene

In this work, we studied the reaction mechanisms for CO2 reduction reaction (CRR) on the iron-doped graphene and its coordinating sulfur (S) and nitrogen (N) variants, FeNn S4-n (n=1-4), using density functional theory calculations. Our results revealed that the electronic property and catalytic reactivity of the surfaces can be tuned by varying the N and S atoms ratio. The CRR activities of the mixed surfaces, FeN3 S1 , FeN2 S2 , and FeN1 S3 , were better than FeN4 and FeS4 , where the absolute value of the limiting potential of the mixed surface decreased by 0.3 V. Considering the stability, we suggest FeN3 S surface to be favorable for CRR. For the bare surfaces, we found a positive linear correlation between the magnetic moment and the charge of Fe metal. For these surfaces, the reduction of CO (*CO+(H+ +e- )→*CHO) was important in deciding the limiting potential. We found that the adsorption energy of CO displayed a volcano relationship with the magnetic moment of the Fe atom. The study showed that the change of local coordinating structure around the Fe atom could modify the electronic and magnetic properties of the active Fe center and improve the CRR activity performance.

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.

Real flue gas CO2 hydrogenation to formate by an enzymatic reactor using O2- and CO-tolerant hydrogenase and formate dehydrogenase

It is challenging to capture carbon dioxide (CO2), a major greenhouse gas in the atmosphere, due to its high chemical stability. One potential practical solution to eliminate CO2 is to convert CO2 into formate using hydrogen (H2) (CO2 hydrogenation), which can be accomplished with inexpensive hydrogen from sustainable sources. While industrial flue gas could provide an adequate source of hydrogen, a suitable catalyst is needed that can tolerate other gas components, such as carbon monoxide (CO) and oxygen (O2), potential inhibitors. Our proposed CO2 hydrogenation system uses the hydrogenase derived from Ralstonia eutropha H16 (ReSH) and formate dehydrogenase derived from Methylobacterium extorquens AM1 (MeFDH1). Both enzymes are tolerant to CO and O2, which are typical inhibitors of metalloenzymes found in flue gas. We have successfully demonstrated that combining ReSH- and MeFDH1-immobilized resins can convert H2 and CO2 in real flue gas to formate via a nicotinamide adenine dinucleotide-dependent cascade reaction. We anticipated that this enzyme system would enable the utilization of diverse H2 and CO2 sources, including waste gases, biomass, and gasified plastics.

A Molecular Z-Scheme Artificial Photosynthetic System Under the Bias-Free Condition for CO2 Reduction Coupled with Two-electron Water Oxidation: Photocatalytic Production of CO/HCOOH and H2 O2

Bio-inspired molecular-engineered systems have been extensively investigated for the half-reactions of H2 O oxidation or CO2 reduction with sacrificial electron donors/acceptors. However, there has yet to be reported a device for dye-sensitized molecular photoanodes coupled with molecular photocathodes in an aqueous solution without the use of sacrificial reagents. Herein, we will report the integration of SnIV - or AlIII -tetrapyridylporphyrin (SnTPyP or AlTPyP) decorated tin oxide particles (SnTPyP/SnO2 or AlTPyP/SnO2 ) photoanode with the dye-sensitized molecular photocathode on nickel oxide particles containing [Ru(diimine)3 ]2+ as the light-harvesting unit and [Ru(diimine)(CO)2 Cl2 ] as the catalyst unit covalently connected and fixed within poly-pyrrole layer (RuCAT-RuC2 -PolyPyr-PRu/NiO). The simultaneous irradiation of the two photoelectrodes with visible light resulted in H2 O2 on the anode and CO, HCOOH, and H2 on the cathode with high Faradaic efficiencies in purely aqueous conditions without any applied bias is the first example of artificial photosynthesis with only two-electron redox reactions.

Theoretical exploration on the performance of single and dual-atom Cu catalysts on the CO2 electroreduction process: a DFT study

Carbon dioxide (CO2) electroreduction by metal-nitrogen-doped carbon (MNC) catalysts is a promising and efficient method to mitigate global warming by converting CO2 molecules to value-added chemicals. In this research, we systematically studied the behaviours of single and dual-atom Cu catalysts during the CO2 electroreduction process using density functional theory (DFT) calculations. Two structures, i.e., CuNC-4-pyridine and CuCuNC-4a, were found to be beneficial for C2 chemical generation with relatively high stabilities. Subsequently, we explored the detailed pathways of key products (CO, HCOOH, CH3OH, CH4, C2H6O, C2H4 and C2H6) during CO2 electroreduction on CuNC-4-pyridine and CuCuNC-4a. This research reveals the mechanisms of key product formation during CO2 electroreduction on CuNC-4-pyridine and CuCuNC-4a, which would provide important insights to guide the design of MNC catalysts with low limiting potentials and high product selectivity.

Hydrogenation of CO2 to MeOH Catalyzed by Highly Robust (PNNP)Ir Complexes Activated by Alkali Bases in Alcohol

Despite receiving significant attention, well-defined homogeneous complexes for hydrogenation of carbon dioxide (CO2) to methanol (MeOH) are scarce and suffer issues of low catalyst turnover numbers (TONs) at high catalyst concentrations and deactivation in the presence of CO and at elevated temperatures. Herein, we disclose a system deploying sterically demanded (PNNP)Ir complexes for a sustained activity for hydrogenation of CO2 to MeOH at temperatures ∼200 °C in an alcohol solvent. Through reaction optimization, we achieved a TON of ∼9000 for MeOH formation, which exceeds most active homogeneous systems reported to date, and robustness on par with or exceeding most reactive systems utilizing amine additives was demonstrated. The key to achieving sustained catalyst turnover for the system was utilizing a catalytic amount of an alkali base additive, which serves the dual purpose of facilitating more efficient outer-sphere reduction of CO2 and HCO2Et and enhancing the selectivity of MeOH over in situ formed CO.

Cu-catalyzed carboxylation of organoboronic acid pinacol esters with CO2

Chemical fixation of CO2 has received much attention. In particular, catalytic C-C bond formation with CO2 giving carboxylic acids is of great significance. Among the CO2 fixation methods, multiple carboxylation is one of the challenging subjects. Here we investigated the Cu-catalyzed carboxylation of a variety of boronic acid pinacol esters (C(sp2)-, C(sp3)-, and C(sp)-B compounds) with CO2, which efficiently provided the corresponding products, including aryl, alkenyl, alkyl, and alkynyl carboxylic acids. This carboxylation was also applicable to multiple CO2 fixation giving di- and tri-carboxylic acids under robust reaction conditions (totally 29 examples).

Comparative study of CO2 insertion into pincer supported palladium alkyl and aryl complexes

The insertion of CO2 into metal alkyl bonds is a crucial elementary step in transition metal-catalyzed processes for CO2 utilization. Here, we synthesize pincer-supported palladium complexes of the type (tBuPBP)Pd(alkyl) (tBuPBP = B(NCH2PtBu2)2C6H4-; alkyl = CH2CH3, CH2CH2CH3, CH2C6H5, and CH2-4-OMe-C6H4) and (tBuPBP)Pd(C6H5) and compare the rates of CO2 insertion into the palladium alkyl bonds to form metal carboxylate complexes. Although, the rate constant for CO2 insertion into (tBuPBP)Pd(CH2CH3) is more than double the rate constant we previously measured for insertion into the palladium methyl complex (tBuPBP)Pd(CH3), insertion into (tBuPBP)Pd(CH2CH2CH3) occurs approximately one order of magnitude slower than (tBuPBP)Pd(CH3). CO2 insertion into the benzyl complexes (tBuPBP)Pd(CH2C6H5) and (tBuPBP)Pd(CH2-4-OMe-C6H4) is significantly slower than any of the n-alkyl complexes, and CO2 does not insert into the palladium phenyl bond of (tBuPBP)Pd(C6H5). While (tBuPBP)Pd(CH2CH3) and (tBuPBP)Pd(CH2CH2CH3) are resistant to β-hydride elimination, we were unable to synthesize complexes with n-butyl, iso-propyl, and tert-butyl ligands due to β-hydride elimination and an unusual reductive coupling, which involves the formation of new C-B bonds. This reductive process also occurred for (tBuPBP)Pd(CH2C6H5) at elevated temperature and a related process involving the formation of a new H-B bond prevented the isolation of (tBuPBP)PdH. DFT calculations provide insight into the relative rates of CO2 insertion and indicate that steric factors are critical. Overall, this work is one of the first comparative studies of the rates of CO2 insertion into different metal alkyl bonds and provides fundamental information that may be important for the development of new catalysts for CO2 utilization.

Porphyrinic Porous Aromatic Frameworks for Carbon Dioxide Adsorption and Separation

The capture of carbon dioxide (CO2 ) from industrial process emissions is increasingly important for the mitigation and prevention of the disruptive effects of global warming. In this study, PAF (porous aromatic frameworks)-TPB(1,3,5-triphenylbenzene) and three-dimensional PAF-TPM (tetraphenylmethane) porphyrin-based aromatic porous materials were synthesized through the Scholl reaction. The CO2 and N2 adsorption isotherms at 273 K and 298 K were studied to determine the performance in carbon dioxide capture at flue gas conditions. There is a significant difference in the adsorption capacity of the two materials for CO2 and N2 , so they can be used for CO2 /N2 adsorption separation. PAF-TPM has better CO2 /N2 separation at low pressure (150 mbar), while PAF-TPB has the advantage of greater CO2 /N2 separation at high pressure (1 bar). It can be applied to CO2 adsorption separation at low and high pressure, respectively. In particular, PAF-TPB has a CO2 /N2 separation efficiency of up to 100.9 at 1 bar and 273 K. This work provides ideas for the design and synthesis of organic porous materials for the adsorption separation of CO2 and N2 .

Unlocking full and fast conversion in photocatalytic carbon dioxide reduction for applications in radio-carbonylation

Harvesting sunlight to drive carbon dioxide (CO₂) valorisation represents an ideal concept to support a sustainable and carbon-neutral economy. While the photochemical reduction of CO₂ to carbon monoxide (CO) has emerged as a hot research topic, the full CO₂-to-CO conversion remains an often-overlooked criterion that prevents a productive and direct valorisation of CO into high-value-added chemicals. Herein, we report a photocatalytic process that unlocks full and fast CO₂-to-CO conversion (<10 min) and its straightforward valorisation into human health related field of radiochemistry with carbon isotopes. Guided by reaction-model-based kinetic simulations to rationalize reaction optimisations, this manifold opens new opportunities for the direct access to ¹¹C- and ¹⁴C-labeled pharmaceuticals from their primary isotopic sources [¹¹C]CO₂ and [¹⁴C]CO₂.

Carbon neutral hydrogen storage and release cycles based on dual-functional roles of formamides

The development of alternative clean energy carriers is a key challenge for our society. Carbon-based hydrogen storage materials are well-suited to undergo reversible (de)hydrogenation reactions and the development of catalysts for the individual process steps is crucial. In the current state, noble metal-based catalysts still dominate this field. Here, a system for partially reversible and carbon-neutral hydrogen storage and release is reported. It is based on the dual-functional roles of formamides and uses a small molecule Fe-pincer complex as the catalyst, showing good stability and reusability with high productivity. Starting from formamides, quantitative production of CO-free hydrogen is achieved at high selectivity ( > 99.9%). This system works at modest temperatures of 90 °C, which can be easily supplied by the waste heat from e.g., proton-exchange membrane fuel cells. Employing such system, we achieve >70% H₂ evolution efficiency and >99% H₂ selectivity in 10 charge-discharge cycles, avoiding undesired carbon emission between cycles.