Highlights and challenges in the selective reduction of carbon dioxide to methanol

Electrochemical Reduction of CO2 to CH3OH Catalyzed by an Iron Porphyrinoid

Designing catalysts for the selective reduction of CO2, resulting in products having commercial value, is an important area of contemporary research. Several molecular catalysts have been reported to facilitate the reduction of CO2 (both electrochemical and photochemical) to yield 2e-/2H+ electron-reduced products, CO and HCOOH, and selective reduction of CO2 beyond 2e-/2H+ is rare. This is partly because the factors that control the selectivity of CO2 reduction beyond 2e- are not yet understood. An iron chlorin complex with a pendent amine functionality in its second sphere, known to selectively catalyze CO2RR to HCOOH with a very low overpotential from its formal Fe(I) state, can catalyze CO2RR from its formal Fe(0) state by 6e-/6H+, forming CH3OH as a major product with a Faradaic yield of ∼50%. Mechanistic investigations using in situ spectro-electrochemistry indicate that the reactivity of a low-spin d7 FeI-COOH intermediate species generated during CO2RR is crucial in determining the product selectivity of this reaction. In weakly acidic conditions, C-protonation of this FeI-COOH species, which is also chemically prepared and spectroscopically characterized, leads to HCOOH. The O-protonation, leading to C-OH bond cleavage and eventually to CH3OH, is ∼3 kcal/mol higher in energy and can be achieved in more acidic solutions. Hydrogen bonding to the pendent amine in the catalyst stabilizes reactive intermediates formed in the CO2RR and enables 6e-/6H+ reduction of CO2 to CH3OH.

Partial PdAu nanoparticle embedding into TiO2 support accentuates catalytic contributions from the Au/TiO2 interface

Despite the broad catalytic relevance of metal-support interfaces, controlling their chemical nature, the interfacial contact perimeter (exposed to reactants), and consequently, their contributions to overall catalytic reactivity, remains challenging, as the nanoparticle and support characteristics are interdependent when catalysts are prepared by impregnation. Here, we decoupled both characteristics by using a raspberry-colloid-templating strategy that yields partially embedded PdAu nanoparticles within well-defined SiO2 or TiO2 supports, thereby increasing the metal-support interfacial contact compared to nonembedded catalysts that we prepared by attaching the same nanoparticles onto support surfaces. Between nonembedded PdAu/SiO2 and PdAu/TiO2, we identified a support effect resulting in a 1.4-fold higher activity of PdAu/TiO2 than PdAu/SiO2 for benzaldehyde hydrogenation. Notably, partial nanoparticle embedding in the TiO2 raspberry-colloid-templated support increased the metal-support interfacial perimeter and consequently, the number of Au/TiO2 interfacial sites by 5.4-fold, which further enhanced the activity of PdAu/TiO2 by an additional 4.1-fold. Theoretical calculations and in situ surface-sensitive desorption analyses reveal facile benzaldehyde binding at the Au/TiO2 interface and at Pd ensembles on the nanoparticle surface, explaining the connection between the number of Au/TiO2 interfacial sites (via the metal-support interfacial perimeter) and catalytic activity. Our results demonstrate partial nanoparticle embedding as a synthetic strategy to produce thermocatalytically stable catalysts and increase the number of catalytically active Au/TiO2 interfacial sites to augment catalytic contributions arising from metal-support interfaces.

Electron Transport Chains Promote Selective Photocatalytic Conversion of CO2 to Methanol

The photocatalytic conversion of carbon dioxide (CO2) into "liquid sunshine" methanol (CH3OH) using semiconductor catalysts has garnered significant attention. Increasing the number of effective electrons and regulating reaction pathways is the key to improving the activity and selectivity of CH3OH. Due to the electron transport properties of semiconductor heterojunctions and reduced graphene oxide (rGO), a CoS/CoS2-rGO nanocomposite was constructed and applied to the photocatalytic reduction of CO2 to CH3OH. The optimized CoS/CoS2-rGO-5 photocatalyst achieved a CH3OH production rate of 15.26 μmol·g-1 and a selectivity of 42%, which were higher than those of CoS and CoS/CoS2. This is mainly attributed to the fact that CoS/CoS2 and rGO jointly constructed efficient electron transport chains, which not only ensure that photogenerated electrons can achieve orderly and directional migration but also innovatively establish a dual reaction site mechanism, providing strong support for improving photocatalytic activity and selectivity of CH3OH. The design of composite catalysts by coupling of semiconductor heterojunctions with carbon material affords new territory for efficient photogenerated electron transport and provides alternative pathways for photocatalytic CO2 conversion.

Efficient amine-assisted CO2 hydrogenation to methanol co-catalyzed by metallic and oxidized sites within ruthenium clusters

Amine-assisted two-step CO2 hydrogenation is an efficient route for methanol production. To maximize the overall catalytic performance, both the N-formylation of amine with CO2 (i.e., first step) and the subsequent amide hydrogenation (i.e., second step) are required to be optimized. Herein, a class of Al2O3-supported Ru catalysts, featuring multiple activated Ru species (i.e., metallic and oxidized Ru), are rationally fabricated. Density functional theory calculations suggest that metallic Ru forms are preferred for N-formylation step, whereas oxidized Ru species demonstrate enhanced amide hydrogenation activity. Thus, the optimal catalyst, containing unique Ru clusters with coexisting metallic and oxidized Ru species, efficiently synergize the conversion of CO2 into methanol with exceptional selectivity (>95%) in a one-pot two-step process. This work not only presents an advanced catalyst for CO2-based methanol production but also highlights the strategic design of catalysts with multiple active species for optimizing the catalytic performances of multistep reactions in the future.

GC-DFT-Based Dynamic Product Distribution Reveals Enhanced CO2-to-Methanol Electrocatalysis Durability by Heterogeneous CoPc

Heterogeneous cobalt phthalocyanine has emerged as a promising molecular catalyst for electrochemical reduction of CO2 to methanol. Boosting both electrocatalytic durability and selectivity remains a great challenge, which is more difficult with unknown regulation factors for the HER side reaction. Herein, to discover the key to balancing the durability and selectivity, as well as HER regulation, we carried out GC-DFT calculations, based on which dynamic product distribution modeling was conducted to visually present the variation of the product distribution within the applied voltage range. The strongly electron-donating NMe2-substituted CoPc is found to be an excellent candidate. The dynamic product distribution reveals that the key to selectivity and durability balance is to regulate both the potential of the highest methanol Faradaic efficiency and the corresponding energy barrier of the selectivity-determining step for hydrogenated CoPc. The pivotal factor in HER regulation stems from hindered H adsorption due to ligand hydrogenation, arising from the decreased Co-to-H charge transfer. The dynamic product distribution analysis provides intuitive theoretical guidance for highly selective and durable CO2 electroreduction.

Effect of Transition Metal Variability in NNN-Pincer Complexes on Catalytic CO2 Reduction to Methanol

The catalytic efficiency of M-H2tpda pincer complexes (M=Mn(I), Fe(II), Co(III)) in CO2 hydrogenation, emphasizing the role of transition metal variability have been discussed. The DFT analysis demonstrates that complexes with low αR values form weaker M-H bonds, enhancing catalyst reactivity with the elongation of M-H bond. The analysis further displays excellent catalytic performance for Mn-H2tpda (ΔE=20.3 kcal/mol), Fe-H2tpda (ΔE=21.0 kcal/mol) and Co-H2tpda (ΔE=23.6 kcal/mol) for CO2 to formic acid formation. The Co-H2tpda (ΔE=16.7 kcal/mol) is comparatively better than Mn-H2tpda (ΔE=20.7 kcal/mol) and Fe-H2tpda (ΔE=19.6 kcal/mol) in formaldehyde formation. All three catalysts exhibit excellent catalytic performance in the conversion of formaldehyde to methanol. The condensed Fukui function calculations of these catalyst complexes establish direct relationship between the ΔE for the rate limiting catalytic cycle and the electrophilicity of the metal centers. The TOF calculations further helped to understand the catalytic performance of the catalysts at various temperatures.

Host-Guest Interactions of Metal-Organic Framework Enable Highly Conductive Quasi-Solid-State Electrolytes for Li-CO2 Batteries

High-energy lithium (Li)-based batteries, especially rechargeable Li-CO2 batteries with CO2 fixation capability and high energy density, are desirable for electrified transportation and other applications. However, the challenges of poor stability, low energy efficiency, and leakage of liquid electrolytes hinder the development of Li-CO2 batteries. Herein, a highly conductive and stable metal-organic framework-encapsulated ionic liquid (IL@MOF) electrolyte system is developed for quasi-solid-state Li-CO2 batteries. Benefiting from the host-guest interaction of MOFs with open micromesopores and internal IL, the optimized IL@MOF electrolytes exhibit a high ionic conductivity of 1.03 mS cm-1 and a high transference number of 0.80 at room temperature. The IL@MOF electrolytes also feature a wide electrochemical stability window (4.71 V versus Li+/Li) and a wide working temperature (-60 °C ∼ 150 °C). The IL@MOF electrolytes also enable Li+ and electrons transport in the carbon nanotubes-IL@MOF (CNT-IL@MOF) solid cathodes in quasi-solid-state Li-CO2 batteries, delivering a high specific capacity of 13,978 mAh g-1 (50 mA g-1), a long cycle life of 441 cycles (500 mA g-1 and 1000 mAh g-1), and a wide operation temperature of -60 to 150 °C. The proposed MOF-encapsulated IL electrolyte system presents a powerful strategy for developing high-energy and highly safe quasi-solid-state batteries.

Pd-Based Multi-Site Catalysts for Selective CO2-to-Methanol Conversion

Developing a multi-site Pd-based electrocatalyst for CO2-to-C1 conversion with high performance and selectivity in the hydrogenation pathway for the CO2 electroreduction reaction is both desirable and challenging. Here, we develop triple-site metallene (Pd82Bi11In7), which can achieve an unprecedented Faraday efficiency of 72.6 ± 1% for methanol production. X-ray photoelectron spectroscopy analysis indicates that some electrons transfer from In and Bi to Pd inside Pd82Bi11In7, forming local electron-rich Pd-site, local primary electron-deficient center In-site, and local secondary electron-deficient center Bi-site. Meanwhile, Pd82Bi11In7 has stronger adsorption for *COOH and *CO, which avoids the generation of formic acid and CO. Moreover, Pd82Bi11In7 reduces the potential determining step energy barrier and controls the hydrogenation path for direct methanol production. The synergistic effect of the triple-sites enables efficient CO2 electroreduction to methanol.

Room-Temperature Formate Ester Transfer Hydrogenation Enables an Electrochemical/Thermal Organometallic Cascade for Methanol Synthesis from CO2

The reduction of CO2 to synthetic fuels is a valuable strategy for energy storage. However, the formation of energy-dense liquid fuels such as methanol remains rare, particularly under low-temperature and low-pressure conditions that can be coupled to renewable electricity sources via electrochemistry. Here, a multicatalyst system pairing an electrocatalyst with a thermal organometallic catalyst is introduced, which enables the reduction of CO2 to methanol at ambient temperature and pressure. The cascade methanol synthesis proceeds via CO2 reduction to formate by electrocatalyst [Cp*Ir(bpy)Cl]+ (Cp*=pentamethylcyclopentadienyl, bpy=2,2'-bipyridine), Fischer esterification of formate to isopropyl formate catalyzed by trifluoromethanesulfonic acid (HOTf), and thermal transfer hydrogenation of isopropyl formate to methanol facilitated by the organometallic catalyst (H-PNP)Ir(H)3 (H-PNP=HN(C2H4PiPr2)2). The isopropanol solvent plays several crucial roles: activating formate ion as isopropyl formate, donating hydrogen for the reduction of formate ester to methanol via transfer hydrogenation, and lowering the barrier for transfer hydrogenation through hydrogen bonding interactions. In addition to reporting a method for room-temperature reduction of challenging ester substrates, this work provides a prototype for pairing electrochemical and thermal organometallic reactions that will guide the design and development of multicatalyst cascades.

Single-Atom-Layer Metallization of Plasmonic Semiconductor Surface for Selectively Enhancing IR-Driven Photocatalytic Reduction of CO2 into CH4

Efficient harvesting and utilization of abundant infrared (IR) photons from sunlight is crucial for the industrial application of photocatalytic CO2 reduction. Plasmonic semiconductors have significant potential in absorbing low-energy IR photons to generate energetic hot electrons. However, modulating these hot electrons to selectively enhance the activity of CO2 reduction into CH4 remains a challenge. Herein, the study proposes a single-atom-layer (SAL) metallization strategy to enhance the generation of IR-driven hot electrons and facilitate their transfer from plasmonic semiconductors to CO2 for producing CH4. This strategy is demonstrated using a paradigmatic W18O49@W-Sn nanowire array (NWA), where Sn2+ ions are grafted onto exposed O atoms on the surface of plasmonic W18O49 to form a surface W-Sn SAL. The incorporation of Sn single atoms enhances plasmonic absorption in IR light for W18O49 NWA. The W-Sn SAL not only promotes CO2 adsorption and reduces its reaction activation energy barrier but also shifts the endoergic CO-protonation process toward an exoergic reaction pathway. Thus, the W18O49@W-Sn NWA exhibits >98% selectivity for IR-driven CO2 reduction to CH4 with an activity over 9.0 times higher than that of bare W18O49 NWA. This SAL metallization strategy can also be applied to other plasmonic semiconductors for selectively enhancing CO2-to-CH4 reduction reactions.

Transforming carbon dioxide into a methanol surrogate using modular transition metal-free Zintl ions

Although not the only greenhouse gas, CO2 is the poster child. Unsurprisingly, therefore, there is global interest across industrial and academic research in its removal and subsequent valorisation, including to methanol and its surrogates. Although difficult to study, the heterogenous pnictogens represent one important category of catalytic materials for these conversions; their high crustal abundance and low cost offers advantages in terms of sustainability. Here, Zintl clusters based on these elements are studied as homogenous atom-precise models in CO2 reduction. A family of group 13 functionalized pnictogen clusters with the general formula [(R2E)Pn7]2- (E = B, Al, In; Pn = P, As) is synthesized and their catalytic competency in the reduction of CO2 probed. Trends in both turnover numbers and frequencies are compared across this series, and [(iBu2Al)P7]2- found to be very high-performing and recyclable. Electronic structures across the series are compared using density functional theory to provide mechanistic insights.

Near-Unity Photothermal CO2 Hydrogenation to Methanol Based on a Molecule/Nanocarbon Hybrid Catalyst

Solar-driven CO2-to-methanol conversion provides an intriguing route for both solar energy storage and CO2 mitigation. For scalable applications, near-unity methanol selectivity is highly desirable to reduce the energy and cost endowed by low-value byproducts and complex separation processes, but so far has not been achieved. Here we demonstrate a molecule/nanocarbon hybrid catalyst composed of carbon nanotube-supported molecularly dispersed cobalt phthalocyanine (CoPc/CNT), which synergistically integrates high photothermal conversion capability for affording an optimal reaction temperature with homogeneous and intrinsically-efficient active sites, to achieve a catalytic activity of 2.4 mmol gcat -1 h-1 and selectivity of ~99 % in direct photothermal CO2 hydrogenation to methanol reaction. Both theoretical calculations and operando characterizations consistently confirm that the unique electronic structure of CoPc and appropriate reaction temperature cooperatively enable a thermodynamic favorable reaction pathway for highly selective methanol production. This work represents an important milestone towards the development of advanced photothermal catalysts for scalable and cost-effective CO2 hydrogenation.

Confinement Synthesis of Atomic Copper-Anchored Polymeric Carbon Nitride in Crystalline UiO-66-NH2 for High-Performance CO2-to-CH3OH Photocatalysis

Photocatalytic CO2 reduction to value-added fuels displays an attractive scenario to enhance energy supply and reduce global warming. We report herein the confinement synthesis of polymeric carbon nitride (PCN) incorporating with Cu single atoms (CuSAs) inside the crystalline UiO-66-NH2, which combines the merits of heterojunction photocatalysis and single-atom catalysis (SAC) to achieve high-performance CO2-to-CH3OH conversion. A series of spectral studies displays the formation of CuSAs@PCN inside the crystalline UiO-66-NH2. Remarkably, the ternary composite shows an excellent photocatalytic turnover frequency of 4.15 mmol ⋅ h-1 ⋅ g-1 for CO2-to-CH3OH conversion. Theoretical and experimental studies demonstrate the doping of CuSAs, as well as the formation of type-II heterojunction, are causal factors to achieve CH3OH generation. The study provides new insights designing high-performance photocatalyst for CO2 conversion to fuels at atomic scale.

Ogataea polymorpha as a next-generation chassis for industrial biotechnology

Ogataea (Hansenula) polymorpha is a nonconventional yeast with some unique characteristics, including fast growth, thermostability, and broad substrate spectrum. Other than common applications for protein production, O. polymorpha is attracting interest for chemical and protein production from methanol; a promising feedstock for the next-generation biomanufacturing due to its abundant sources and excellent characteristics. Benefiting from the development of synthetic biology, it has been engineered to produce value-added chemicals by extensively rewiring cellular metabolism. This Review discusses recently developed synthetic biology tools of O. polymorpha. The advances of chemicals production and systems biology were reviewed comprehensively. Finally, we look ahead to the developments of biomanufacturing in O. polymorpha to make an overall understanding of this chassis for academia and industry.

CO2 Hydrogenation on Carbides Formed in situ on Carbon-Supported Iron-Based Catalysts in High-Density Supercritical Medium

CO2 conversion via hydrogenation over iron-based catalysts on non-carbon supports produces mainly CO or methane by the Sabatier reaction, while the formation of C2+ hydrocarbons is of greatest interest. CxHy production from CO2 may be considered as a two-step process with the initial formation of carbon monoxide by the reverse water gas shift reaction followed by the Fischer-Tropsch synthesis (FTS). In the present work CO2 hydrogenation over iron-based catalysts (Fe, FeCr, FeK) deposited on a carbon carrier has been studied. The catalyst structure has been investigated by XRD, TEM, XPS, Mössbauer spectroscopy and in situ magnetometry. Spinel-type oxide phases (magnetite Fe3O4; maggemite γ-Fe2O3, and, in the case of FeCr/C catalyst, iron chromite Fe1+xCr2-xO4) are formed on the catalysts, and they contribute exclusively to the CO production. Iron carbides, active in FTS, are formed on Fe- and FeK-catalysts during pre-activation in reducing environment and then during the reaction. The reaction over the 20Fe1K/C catalyst in supercritical high-density CO2/H2 substrate (400 °C, 8.5 MPa) leads to 72 % selectivity for C1-C12+ hydrocarbons (alkanes and alkenes). Under the same conditions, iron carbides do not form on the FeCr/C catalysts, and CO2 hydrogenation results in the CO formation with the selectivity of 90-100 %.

Entropy-Derived Synthesis of the CuPd Sub-1nm Alloy for CO2-to-acetate Electroreduction

Bimetallic alloys exhibit remarkable properties in catalysis and energy storage, while their precise synthesis at the subnanoscale remains a formidable challenge due to their immiscible nature in thermodynamics. In this study, we engineer an atomically dispersed CuPd alloy with an average size of 1.5 nm loaded on CuO and phosphomolybdic acid (PMA) coassembly subnanosheets (CuO-PMA SNSs). Driven by the high vibrational entropy, Cu atoms could escape from CuO supports and bond with adjacent Pd single atoms, leading to the in situ formation of CuPd alloys. Furthermore, this strategy can also be utilized for synthesizing the ZnPt alloy with an average size of 1 nm, thereby providing a general pathway for the design of immiscible subnanoalloys. The fully exposed Cu-Pd pairs in CuPd subnanoalloys significantly enhance the adsorption and coverage of surface *CO during the electrochemical reduction of CO2, thereby leading to enhanced stability of ethenone intermediates and facilitating the production of C2 compounds. The resulting CuPd subnanoalloy exhibits a remarkable Faradaic efficiency of 46.5 ± 2.1% for CO2-to-acetate electroreduction and achieves a high acetate productivity of 99 ± 2.8 μmol cm-2 at -0.7 V versus RHE.

In Situ Oxidative Ring-Opening of Calix[8]arene to Construct Stable Bismuth-Oxo Clusters with Exposed Catalytic Sites for Specific Electroreduction of CO2 to HCOOH

Nanocluster catalysts typically face challenges in balancing stability with catalytic efficiency. This study introduces a unique bismuth-oxo cluster, solely protected by two ring-opened calixarenes, which demonstrates not only enhanced structural stability but also superior catalytic performance in the sustained conversion of CO2 to HCOOH via electrocatalysis. For the first time, we reveal that under specific solvothermal conditions, tert-butylcalix[8]arene (TBC[8]) can undergo in situ oxidative cleavage of its C-C bond, leading to ring-opened polyphenolic molecules. These molecules serve as protective ligands for the bismuth-oxo cluster, bestowing exceptional structural stability and offering a more flexible and diverse configuration compared to intact TBC[8]. This adaptability promotes the exposure of active bismuth sites on the cluster surface, enhancing catalytic efficiency. Notably, the Bi10 cluster, featuring a monobismuth active site, achieves an exceptional formate production efficiency of 98.79% at -1.25 V vs RHE while maintaining superb durability over 8 h. The stability and catalytic processes of Bi10 surpass those of the Bi13 cluster, which is structurally reinforced by two intact TBC[8] molecules and stabilized by four benzoic ligands. Through in situ infrared spectroscopy and density functional theory calculations, we demonstrate that the monobismuth active site in Bi10 more effectively stabilizes the *OCHO intermediate, thereby promoting the electrocatalytic reduction of CO2 to HCOOH compared to Bi13. This comparative performance underscores the potential of ring-opened calixarene ligands in enhancing the functionality of nanocluster catalysts.

Redefining the Symphony of Light Aromatic Synthesis Beyond Fossil Fuels: A Journey Navigating through a Fe-Based/HZSM-5 Tandem Route for Syngas Conversion

The escalating concerns about traditional reliance on fossil fuels and environmental issues associated with their exploitation have spurred efforts to explore eco-friendly alternative processes. Since then, in an era where the imperative for renewable practices is paramount, the aromatic synthesis industry has embarked on a journey to diversify its feedstock portfolio, offering a transformative pathway toward carbon neutrality stewardship. This Review delves into the dynamic landscape of aromatic synthesis, elucidating the pivotal role of renewable resources through syngas/CO2 utilization in reshaping the industry's net-zero carbon narrative. Through a meticulous examination of recent advancements, the current Review navigates the trajectory toward admissible aromatics production, highlighting the emergence of Fischer-Tropsch tandem catalysis as a game-changing approach. Scrutinizing the meliorated interplay of Fe-based catalysts and HZSM-5 molecular sieves would uncover the revolutionary potential of rationale design and optimization of integrated catalytic systems in driving the conversion of syngas/CO2 into aromatic hydrocarbons (especially BTX). In essence, the current Review would illuminate the path toward cutting-edge research through in-depth analysis of the transformative power of tandem catalysis and its capacity to propel carbon neutrality goals by unraveling the complexities of renewable aromatic synthesis and paving the way for a carbon-neutral and resilient tomorrow.

Uncertainty Quantification of Linear Scaling, Machine Learning, and Density Functional Theory Derived Thermodynamics for the Catalytic Partial Oxidation of Methane on Rhodium

Accurate and complete microkinetic models (MKMs) are powerful for anticipating the behavior of complex chemical systems at different operating conditions. In heterogeneous catalysis, they can be further used for the rapid development and screening of new catalysts. Density functional theory (DFT) is often used to calculate the parameters used in MKMs with relatively high fidelity. However, given the high cost of DFT calculations for adsorbates in heterogeneous catalysis, linear scaling relations (LSRs) and machine learning (ML) models were developed to give rapid estimates of the parameters in MKM. Regardless of the method, few studies have attempted to quantify the uncertainty in catalytic MKMs, as the uncertainties are often orders of magnitude larger than those for gas phase models. This study explores uncertainty quantification and Bayesian Parameter Estimation for thermodynamic parameters calculated by DFT, LSRs, and GemNet-OC, a ML model developed under the Open Catalyst Project. A model for catalytic partial oxidation of methane (CPOX) on Rhodium was chosen as a case study, in which the model's thermodynamic parameters and their associated uncertainties were determined using DFT, LSR, and GemNet-OC. Markov Chain Monte Carlo coupled with Ensemble Slice Sampling was used to sample the highest probability density (HPD) region of the posterior and determine the maximum of the a posteriori (MAP) for each thermodynamic parameter included. The optimized microkinetic models for each of the three estimation methods had quite similar mechanisms and agreed well with the experimental data for gas phase mole fractions. Exploration of the HPD region of the posterior further revealed that adsorbed hydroxide and oxygen likely bind on facets other than Rhodium 111. The demonstrated workflow addresses the issue of inaccuracies arising from the integration of data from multiple sources by considering both experimental and computational uncertainties, and further reveals information about the active site that would not have been discovered without considering the posterior.

Electrostatic Self-Assembly Synthesis of Pd/In2O3 Nanocatalysts with Improved Performance Toward CO2 Hydrogenation to Methanol

CO2 hydrogenation to methanol has emerged as a promising strategy for achieving carbon neutrality and mitigating global warming, in which the supported Pd/In2O3 catalysts are attracting great attention due to their high selectivity. Nonetheless, conventional impregnation methods induce strong metal-support interaction (SMSI) between Pd and In2O3, which leads to the excessive reduction of In2O3 and the formation of undesirable PdIn alloy in hydrogen-rich atmospheres. Herein, we innovatively synthesized Pd/In2O3 nanocatalysts by the electrostatic self-assembly process between surface-modified composite precursors with opposite charges. And the organic ligands concurrently serve as Pd nanoparticle protective agents. The resultant Pd/In2O3 nanocatalyst demonstrates the homogeneous distribution of Pd nanoparticles with controllable sizes on In2O3 supports and the limited formation of PdIn alloy. As a result, it exhibits superior selectivity and stability compared to the counterparts synthesized by the conventional impregnation procedure. Typically, it attains a maximum methanol space-time yield of 0.54 gMeOH h-1gcat -1 (300 °C, 3.5 MPa, 21,000 mL gcat -1 h-1). Notably, the correlation characterization results reveal the significant effect of small-size, highly dispersed Pd nanoparticles in mitigating MSI. These results provide an alternative strategy for synthesizing highly efficient Pd/In2O3 catalysts and offer a new insight into the strong metal-support interaction.

State of Play of Critical Mineral-Based Catalysts for Electrochemical E-Refinery to Synthetic Fuels

The pursuit of decarbonization involves leveraging waste CO2 for the production of valuable fuels and chemicals (e.g., ethanol, ethylene, and urea) through the electrochemical CO2 reduction reactions (CO2RR). The efficacy of this process heavily depends on electrocatalyst performance, which is generally reliant on high loading of critical minerals. However, the supply of these minerals is susceptible to shortage and disruption, prompting concerns regarding their usage, particularly in electrocatalysis, requiring swift innovations to mitigate the supply risks. The reliance on critical minerals in catalyst fabrication can be reduced by implementing design strategies that improve the available active sites, thereby increasing the mass activity. This review seeks to discuss and analyze potential strategies, challenges, and opportunities for improving catalyst activity in CO2RR with a special attention to addressing the risks associated with critical mineral scarcity. By shedding light onto these aspects of critical mineral-based catalyst systems, this review aims to inspire the development of high-performance catalysts and facilitates the practical application of CO2RR technology, whilst mitigating adverse economic, environmental, and community impacts.

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).

Regulated Photocatalytic CO2-to-CH3OH Pathway by Synergetic Dual Active Sites of Interlayer

Herein, composites of nanosheets with van der Waals contacts are employed to disclose how the interlayer-microenvironment affects the product selectivity of carbon dioxide (CO2) photoreduction. The concept of composites of nanosheets with dual active sites is introduced to manipulate the bonding configuration and promote the thermodynamic formation of methanol (CH3OH). As a prototype, the CoNi2S4-In2O3 composites of nanosheets are prepared, in which high-resolution transmission electron microscopy imaging, X-ray photoelectron spectroscopy spectra, and zeta potential tests confirm the presence of van der Waals contacts rather than chemical bonding between the In2O3 nanosheets and the CoNi2S4 nanosheets within the composite. The fabricated CoNi2S4-In2O3 composites of nanosheets exhibit the detection of the key intermediate *CH3O during CO2 photoreduction through in situ Fourier transform infrared spectra, while the In2O3 nanosheets and CoNi2S4 nanosheets alone do not show this capability, further verified by the density functional theory calculations. Accordingly, the CoNi2S4-In2O3 composites of nanosheets show the ability to produce CH3OH, whereas the CoNi2S4 and In2O3 nanosheets solely generate carbon monoxide products from CO2 photoreduction.

Potential-driven structural distortion in cobalt phthalocyanine for electrocatalytic CO2/CO reduction towards methanol

Cobalt phthalocyanine immobilized on carbon nanotube has demonstrated appreciable selectivity and activity for methanol synthesis in electrocatalytic CO2/CO reduction. However, discrepancies in methanol production selectivity and activity between CO2 and CO reduction have been observed, leading to inconclusive mechanisms for methanol production in this system. Here, we discover that the interaction between cobalt phthalocyanine molecules and defects on carbon nanotube substrate plays a key role in methanol production during CO2/CO electroreduction. Through detailed operando X-ray absorption and infrared spectroscopies, we find that upon application of cathodic potential, this interaction induces the transformation of the planar CoN4 center in cobalt phthalocyanine to an out-of-plane distorted configuration. Consequently, this potential induced structural change promotes the transformation of linearly bonded *CO at the CoN4 center to bridge *CO, thereby facilitating methanol production. Overall, these comprehensive mechanistic investigations and the outstanding performance (methanol partial current density over 150 mA cm-2) provide valuable insights in guiding the activity and selectivity of immobilized cobalt phthalocyanine for methanol production in CO2/CO reduction.

Iron(III) Complexes with Pyridine Group Coordination and Dissociation Reversible Equilibrium: Cooperative Activation of CO2 and Epoxides into Cyclic Carbonates

Herein, a series of [ONSN]-type iron(III) complexes were synthesized. A binary catalytic system in combination with iron complexes and tetrabutylammonium bromide (TBAB) exhibited high activity for the synthesis of cyclic carbonates from CO2 (1 atm) and terminal epoxides at room temperature. Additionally, single-component iron complexes without using additional TBAB as nucleophiles also showed high activity for the cycloaddition of CO2 and terminal epoxides under 80 °C and 0.5 MPa of CO2. This study demonstrates that single-component iron catalysts provide a competitive alternative to binary catalytic systems for the synthesis of cyclic carbonates from CO2 and epoxides. Mechanistic studies on a single-component iron catalytic system suggest that the temperature serves as a role of responsive switch for controlling the coordination and dissociation of pyridine bearing iron catalysts detected using in situ infrared spectroscopy, and uncoordinated pyridine activates CO2 to form carbamate. Studies of electrospray ionization high-resolution mass spectrometry reveal that an iron center was used as a Lewis acidic site, free halogen anions from the iron center were used as a nucleophilic site, and coordinated pyridine was released from iron complexes to activate CO2.

Engineering MOF/carbon nitride heterojunctions for effective dual photocatalytic CO2 conversion and oxygen evolution reactions

Photocatalysis appears as one of the most promising avenues to shift towards sustainable sources of energy, owing to its ability to transform solar light into chemical energy, e.g. production of chemical fuels via oxygen evolution (OER) and CO2 reduction (CO2RR) reactions. Ti metal-organic frameworks (MOFs) and graphitic carbon nitride derivatives, i.e. poly-heptazine imides (PHI) are appealing CO2RR and OER photo-catalysts respectively. Engineering of an innovative Z-scheme heterojunction by assembling a Ti-MOF and PHI offers an unparalleled opportunity to mimick an artificial photosynthesis device for dual CO2RR/OER catalysis. Along this path, understanding of the photophysical processes controlling the MOF/PHI interfacial charge recombination is vital to fine tune the electronic and chemical features of the two components and devise the optimum heterojunction. To address this challenge, we developed a modelling approach integrating force field Molecular Dynamics (MD), Time-Dependent Density Functional Theory (TD-DFT) and Non-Equilibrium Green Function DFT (NEGF-DFT) tools with the aim of systematically exploring the structuring, the opto-electronic and transport properties of MOF/PHI heterojunctions. We revealed that the nature of the MOF/PHI interactions, the interfacial charge transfer directionality and the absorption energy windows of the resulting heterojunctions can be fine tuned by incorporating Cu species in the MOF and/or doping PHI with mono- or divalent cations. Interestingly, we demonstrated that the interfacial charge transfer can be further boosted by engineering MOF/PHI device junctions and application of negative bias. Overall, our generalizable computational methodology unravelled that the performance of CO2RR/OER photoreactors can be optimized by chemical and electronic tuning of the components but also by device design based on reliable structure-property rules, paving the way towards practical exploitation.

Carbon Dioxide Capture and Conversion Using Metal-Organic Framework (MOF) Materials: A Comprehensive Review

The escalating threat of anthropogenic climate change has spurred an urgent quest for innovative CO2 capture and utilization (CCU) technologies. Metal-organic frameworks (MOFs) have emerged as prominent candidates in CO2 capture and conversion due to their large specific surface area, well-defined porous structure, and tunable chemical properties. This review unveils the latest advancements in MOF-based materials specifically designed for superior CO2 adsorption, precise separation, advanced photocatalytic and electrocatalytic CO2 reduction, progressive CO2 hydrogenation, and dual functionalities. We explore the strategies that enhance MOF efficiency and examine the challenges of and opportunities afforded by transitioning from laboratory research to industrial application. Looking ahead, this review offers a visionary perspective on harnessing MOFs for the sustainable capture and conversion of CO2.

Achieving Almost 100% Selectivity in Photocatalytic CO2 Reduction to Methane via In-Situ Atmosphere Regulation Strategy

Artificial photosynthesis, harnessing solar energy to convert CO2 into hydrocarbons, presents a promising solution for climate change and energy scarcity. However, photocatalytic CO2 reduction often terminates at the CO stage due to limited electron transfer capacity, hindering the formation of higher-energy hydrocarbons such as CH4. This study introduces, for the first time, an in-situ atmosphere regulation strategy, refined from molecular imprinting methodologies, using dynamically reacting molecules to precisely engineer photocatalytic surface sites for selective *CO adsorption and hydrogenation in CO2-to-CH4 conversion. Specifically, the single-atom Cu catalyst (Cu-SA-CO) is prepared by anchoring single-atom Cu onto defective TiO2 substrates (Cu-SA-CO) under a CO reduction atmosphere. Under illumination, the catalyst exhibited outstanding CH4 selectivity (almost 100%) and productivity (58.5 µmol g-1 h-1). Mechanistic investigations reveal that the coordination environment of the Cu single atoms is significantly affected by dynamically reacting molecules (CO and *CHxO) during synthesis, leading to a Ti-Cu-O structure. The structure, with the synergistic interaction between Cu single atoms and oxygen defects, significantly enhances *CO adsorption and hydrogenation, thereby promoting the formation of methane. This work pioneers the use of dynamically reactive molecules as imprinted templates to tune photocatalytic CO2 reduction selectivity, providing a novel avenue for designing efficient photocatalysts.

Constructing B─N─P Bonds in Ultrathin Holey g-C3N4 for Regulating the Local Chemical Environment in Photocatalytic CO2 Reduction to CO

The lack of intrinsic active sites for photocatalytic CO2 reduction reaction (CO2RR) and fast recombination rate of charge carriers are the main obstacles to achieving high photocatalytic activity. In this work, a novel phosphorus and boron binary-doped graphitic carbon nitride, highly porous material that exhibits powerful photocatalytic CO2 reduction activity, specifically toward selective CO generation, is disclosed. The coexistence of Lewis-acidic and Lewis-basic sites plays a key role in tuning the electronic structure, promoting charge distribution, extending light-harvesting ability, and promoting dissociation of excitons into active carriers. Porosity and dual dopants create local chemical environments that activate the pyridinic nitrogen atom between the phosphorus and boron atoms on the exposed surface, enabling it to function as an active site for CO2RR. The P-N-B triad is found to lower the activation barrier for reduction of CO2 by stabilizing the COOH reaction intermediate and altering the rate-determining step. As a result, CO yield increased to 22.45 µmol g-1 h-1 under visible light irradiation, which is ≈12 times larger than that of pristine graphitic carbon nitride. This study provides insights into the mechanism of charge carrier dynamics and active site determination, contributing to the understanding of the photocatalytic CO2RR mechanism.

[Ce3+-OV-Ce4+] Located Surface-Distributed Sheet Cu-Zn-Ce Catalysts for Methanol Production by CO2 Hydrogenation

The metal-support interaction is crucial for the performance of Cu-based catalysts. However, the distinctive properties of the support metal element itself are often overlooked in catalyst design. In this paper, a sheet Cu-Zn-Ce with [Ce3+-OV-Ce4+] located on the surface was designed by the sol-gel method. Through EPR and X-ray photoelectron spectroscopy (XPS), the relationship between the content of oxygen vacancies and Ce was revealed. Ce itself induces the generation of [Ce3+-OV-Ce4+]. Through ICP-MS, XPS, and SEM-mapping, the Ce-induced formation of [Ce3+-OV-Ce4+] located on the catalyst surface was demonstrated. CO2-TPD and DFT calculations further revealed that [Ce3+-OV-Ce4+] enhanced CO2 adsorption, leading to a 10% increase in methanol selectivity compared to Cu-Zn-Ce synthesized via the coprecipitation method.

Recent advances in CO2 reduction with renewable reductants under hydrothermal conditions: towards efficient and net carbon benefit CO2 conversion

The ever-growing atmospheric CO2 concentration threatening the environmental sustainability of humankind makes the reduction of CO2 to chemicals or fuels an ideal solution. Two priorities are anticipated for the conversion technology, high efficiency and net carbon benefit, to ensure the mitigation of the CO2 problem both promptly and sustainably. Until now, catalytic hydrogenation or solar/electro-chemical CO2 conversion have achieved CO2 reduction promisingly while, to some extent, compromising to fulfill the two rules, and thus alternative approaches for CO2 reduction are necessary. Natural geochemical processes as abiotic CO2 reductions give hints for efficient CO2 reduction by building hydrothermal reaction systems, and this type of reaction atmosphere provides room for introducing renewable substances as reductants, which offers the possibility to achieve CO2 reduction with net carbon benefit. While the progress in CO2 reduction has been abundantly summarized, reviews on hydrothermal CO2 reduction are relatively scarce and, more importantly, few have focused on CO2 reduction with renewable reductants with the consideration of both scale of efficiency and sustainability. This review provides a fundamental and critical review of metal, biomass and polymer waste as reducing agents for hydrothermal CO2 reduction. Various products including formic acid, methanol, methane and multi-carbon chemicals can be formed, and effects of operational parameters such as temperature, batch holding time, pH value and water filing as well as detailed reaction mechanisms are illustrated. Particularly, the critical roles of high temperature and pressure water as reaction promotor and catalyst in hydrothermal CO2 conversion are discussed at the mechanistic level. More importantly, this review compares hydrothermal CO2 reduction with other methods such as catalytic hydrogenation and photo/electrocatalysis, evaluating their efficiency and potential for net carbon benefit. The aim of this review is to promote the understanding of CO2 activation under a hydrothermal environment and provide insights into the efficient and sustainable strategy of hydrothermal CO2 conversion for future fundamental research and industrial applications.

Hierarchically Ordered Pore Engineering of Metal-Organic Framework-Based Materials for Electrocatalysis

Ordered pore engineering that embeds uniform pores with periodic alignment in electrocatalysts opens up a new avenue for achieving further performance promotion. Hierarchically ordered porous metal-organic frameworks (HOP-MOFs) possessing multilevel pores with ordered distribution are the promising precursors for the exploration of ordered porous electrocatalysts, while the scalable acquisition of HOP-MOFs with editable components and adjustable pore size regimes is critical. This review presents recent progress on hierarchically ordered pore engineering of MOF-based materials for enhanced electrocatalysis. The synthetic strategies of HOP-MOFs with different pore size regimes, including the self-assembly guided by reticular chemistry, surfactant, nanoemulsion, and nanocasting, are first introduced. Then the applications of HOP-MOFs as the precursors for exploring hierarchically ordered porous electrocatalysts are summarized, selecting representatives to highlight the boosted performance. Especially, the intensification of molecule and ion transport integrated with optimized electron transfer and site exposure over the hierarchically ordered porous derivatives are emphasized to clarify the directional transfer and integration effect endowed by ordered pore engineering. Finally, the remaining scientific challenges and an outlook of this field are proposed. It is hoped that this review will guide the hierarchically ordered pore engineering of nanocatalysts for boosting the catalytic performance and promoting the practical applications.

Sustainable methanol production from carbon dioxide: advances, challenges, and future prospects

The urgent need to address global carbon emissions and promote sustainable energy solutions has led to a growing interest in carbon dioxide (CO2) conversion technologies. Among these, the transformation of CO2 into methanol (MeOH) has gained prominence as an effective mitigation strategy. This review paper provides a comprehensive exploration of recent advances and applications in the direct utilization of CO2 for the synthesis of MeOH, encompassing various aspects from catalysts to market analysis, environmental impact, and future prospects. We begin by introducing the current state of CO2 mitigation strategies, highlighting the significance of carbon recycling through MeOH production. The paper delves into the chemistry and technology behind the conversion of CO2 into MeOH, encompassing key themes such as feedstock selection, material and energy supply, and the various conversion processes, including chemical, electrochemical, photochemical, and photoelectrochemical pathways. An in-depth analysis of heterogeneous and homogeneous catalysts for MeOH synthesis is provided, shedding light on the advantages and drawbacks of each. Furthermore, we explore diverse routes for CO2 hydrogenation into MeOH, emphasizing the technological advances and production processes associated with this sustainable transformation. As MeOH holds a pivotal role in a wide range of chemical applications and emerges as a promising transportation fuel, the paper explores its various chemical uses, transportation, storage, and distribution, as well as the evolving MeOH market. The environmental and energy implications of CO2 conversion to MeOH are discussed, including a thermodynamic analysis of the process and cost and energy evaluations for large-scale catalytic hydrogenation.

Gray mesoporous SnO2 catalyst for CO2 electroreduction with high partial current density and formate selectivity

The mesoporous metal oxide semiconductors exhibit unique chemical and physical characteristics, making them highly desirable for catalysis, electrochemistry, energy conversion, and energy storage applications. Here, we report the facial fabrication of mesoporous gray SnO2 (MGS) electrocatalysts employing an evaporation-induced co-assembly (EICA) approach, utilizing poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymers Pluronic P123 (PEO-PPO-PEO) triblock copolymer as a template for electrochemical CO2 reduction reaction (eCO2RR). By sustaining the co-assembly conditions and utilizing a thermal treatment technique based on carbon, gray mesoporous SnO2 materials with a high density of active sites and oxygen vacancies can be constructed. The MGS materials were employed in eCO2RR in a flow cell type, which exhibits excellent catalytic activity and selectivity toward formate with a high partial current density of -234 mA cm-2 and Faradaic efficiency (FE) of 93.60 % at -1.3 V vs. reversible hydrogen electrode (RHE). Interestingly, the mesoporous SnO2 with a 1.5 wt% ratio of Sn precursor to P123 surfactant (MS-1.5@350N-400A) electrode exhibits a high level of Faradaic efficiency (FE) of (98%) at a low overpotential of -0.6 VRHE, which is a seldom recorded performance for similar systems. A stable FE of 96 ± 1% was observed in the range of -0.6 to -1.2 VRHE, which is the result of a large surface area (184 m2/g) and a high number of active sites and oxygen vacancies within the mesostructured framework.

Cobalt-based Polymerized Porphyrinic Network for Visible-light-driven CO2 Reduction

Visible-light-driven conversion of carbon dioxide to valuable compounds and fuels is an important but challenging task due to the inherent stability of the CO2 molecules. Herein, we report a series of cobalt-based polymerized porphyrinic network (PPN) photocatalysts for CO2 reduction with high activity. The introduction of organic groups results in the addition of more conjugated electrons to the networks, thereby altering the molecular orbital levels within the networks. This integration of functional groups effectively adjusts the levels of the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO). The PPN(Co)-NO2 exhibits outstanding performance, with a CO evolution rate of 12 268 μmol/g/h and 85.8% selectivity, surpassing most similar photocatalyst systems. The performance of PPN(Co)-NO2 is also excellent in terms of apparent quantum yield (AQY) for CO production (5.7% at 420 nm). Density functional theory (DFT) calculations, time-resolved photoluminescence (TRPL), and electrochemical tests reveal that the introduction of methyl and nitro groups leads to a narrower energy gap, facilitating a faster charge transfer. The coupling reaction in this study enables the formation of stable C-C bonds, enhancing the structural regulation, active site diversity, and stability of the catalysts for photocatalytic CO2 reduction. This work offers a facile strategy to develop reliable catalysts for efficient CO2 conversion.

Development of Plasmonic Attapulgite/Co(Ti)Ox Nanocomposite Using Spent Batteries toward Photothermal Reduction of CO2

The rapid development of the battery industry has brought about a large amount of waste battery pollution. How to realize the high-value utilization of waste batteries is an urgent problem to be solved. Herein, cobalt and titanium compounds (LTCO) were firstly recovered from spent lithium-ion batteries (LIBs) using the carbon thermal reduction approach, and plasmonic attapulgite/Co(Ti)Ox (H-ATP/Co(Ti)Ox) nanocomposites were prepared by the microwave hydrothermal technique. H-ATP had a large specific surface area and enough active sites to capture CO2 molecules. The biochar not only reduced the spinel phase of waste LIBs into metal oxides including Co3O4 and TiO2 but also increased the separation and transmission of the carriers, thereby accelerating the adsorption and reduction of CO2. In addition, H-ATP/Co(Ti)Ox exhibited a localized surface plasmon resonance effect (LSPR) in the visible to near-infrared region and released high-energy hot electrons, enhancing the surface temperature of the catalyst and further improving the catalytic reduction of CO2 with a high CO yield of 14.7 μmol·g-1·h-1. The current work demonstrates the potential for CO2 reduction by taking advantage of natural mineral and spent batteries.

In Situ Generated CO Enables High-Current CO2 Reduction to Methanol in a Molecular Catalyst Layer

Molecular catalysts such as cobalt phthalocyanine (CoPc) exhibit remarkable electrochemical activity in methanol production from CO2 or CO, but fast conversion with a high current density is still yet to be realized. While adopting flow cells with gas diffusion electrodes is a common approach to enhanced reaction rates, the current scientific and engineering knowledge primarily centers on metal particle-based catalysts like Cu. This focus overlooks the emerging heterogenized molecular catalysts with distinct physical and chemical properties. In this work, we observe that the partial current density of CO reduction to methanol catalyzed by tetraamine-substituted CoPc (CoPc-NH2) supported on carbon nanotubes (CNTs) remains below 30 mA cm-2, even with systematic optimization of structural and operational parameters of the flow cell. A comparative analysis with a Cu metal catalyst reveals that the porous and electrolyte-philic nature of CoPc-NH2/CNT leaves a large fraction of active sites deprived of CO under reaction conditions. To address this microenvironmental challenge, we directly use CO2 as the reactant, leveraging its faster diffusion rate in water compared to CO. Effective CO2 reduction generates CO in situ to feed the catalytic sites, achieving an unprecedently high partial current density for methanol of 129 mA cm-2. This research underscores the necessity for new insights and approaches in the development of molecular catalyst-based electrodes.

Decorating of 2D indium oxide onto 2D bismuth oxybromide to enhance internal electric field and stimulate artificial photosynthesis

CO2 photocatalytic reduction is an excellent strategy for promoting solar-to-chemical energy conversion and alleviating the severe environmental crisis. In this study, 2D indium oxide (IO) is decorated on 2D bismuth oxybromide (BOB) nanosheets to gain BOB/IO (BxIy) heterojunction. The optimal B3I1 composite affords a CO production rate of 54.2 μmol⋅g-1, about 2.2 times and 11.3 times higher than those of the pristine BOB and IO, respectively. The introduction of IO significantly enhances the internal electric field (IEF), leading to accelerated charge transfer and prolonged lifetime of the photogenerated carriers. In the BxIy composite, the BOB and IO serve as the electron acceptor and donor, respectively, facilitating the reduction of CO2 and oxidation of H2O. In-situ DRIFTs spectra are used to confirm the catalytic active sites and provide insights into the mechanism of CO2 photoreduction. The results suggest *COOH and *CO2- species played a crucial role in the formation of CO. This work presents a valuable perspective on understanding the charge transfer route and developing highly efficient photocatalysts for CO2 photoreduction.

Effect of reduction pretreatment on the structure and catalytic performance of Ir-In2O3 catalysts for CO2 hydrogenation to methanol

In2O3 has been found a promising application in CO2 hydrogenation to methanol, which is beneficial to the utilization of CO2. The oxygen vacancy (Ov) site is identified as the catalytic active center of this reaction. However, there remains a great challenge to understand the relations between the state of oxygen species in In2O3 and the catalytic performance for CO2 hydrogenation to methanol. In the present work, we compare the properties of multiple In2O3 and Ir-promoted In2O3 (Ir-In2O3) catalysts with different Ir loadings and after being pretreated under different reduction temperatures. The CO2 conversion rate of Ir-In2O3 is more promoted than that of pure In2O3. With only a small amount of Ir loading, the highly dispersed Ir species on In2O3 increase the concentration of Ov sites and enhance the activity. By finely tuning the catalyst structure, Ir-In2O3 with an Ir loading of 0.16 wt.% and pre-reduction treatment under 300°C exhibits the highest methanol yield of 146 mgCH3OH/(gcat·hr). Characterizations of Raman, electron paramagnetic resonance, X-ray photoelectron spectroscopy, CO2-temperature programmed desorption and CO2-pulse adsorption for the catalysts confirm that more Ov sites can be generated under higher reduction temperature, which will induce a facile CO2 adsorption and desorption cycle. Higher performance for methanol production requires an adequate dynamic balance among the surface oxygen atoms and vacancies, which guides us to find more suitable conditions for catalyst pretreatment and reaction.

Spinel Nanostructures for the Hydrogenation of CO2 to Methanol and Hydrocarbon Chemicals

Composite oxides have been widely applied in the hydrogenation of CO/CO2 to methanol or as the component of bifunctional oxide-zeolite for the synthesis of hydrocarbon chemicals. However, it is still challenging to disentangle the stepwise formation mechanism of CH3OH at working conditions and selectively convert CO2 to hydrocarbon chemicals with narrow distribution. Here, we investigate the reaction network of the hydrogenation of CO2 to methanol over a series of spinel oxides (AB2O4), among which the Zn-based nanostructures offer superior performance in methanol synthesis. Through a series of (quasi) in situ spectroscopic characterizations, we evidence that the dissociation of H2 tends to follow a heterolytic pathway and that hydrogenation ability can be regulated by the combination of Zn with Ga or Al. The coordinatively unsaturated metal sites over ZnAl2Ox and ZnGa2Ox originating from oxygen vacancies (OVs) are evidenced to be responsible for the dissociative adsorption and activation of CO2. The evolution of the reaction intermediates, including both carbonaceous and hydrogen species at high temperatures and pressures over the spinel oxides, has been experimentally elaborated at the atomic level. With the integration of a series of zeolites or zeotypes, high selectivities of hydrocarbon chemicals with narrow distributions can be directly produced from CO2 and H2, offering a promising route for CO2 utilization.

Reverse water-gas shift catalyzed by RhnVO3,4- (n = 3-7) cluster anions under variable temperatures

A fundamental understanding of the exact structural characteristics and reaction mechanisms of interface active sites is vital to engineering an energetic metal-support boundary in heterogeneous catalysis. Herein, benefiting from a newly developed high-temperature ion trap reactor, the reverse water-gas shift (RWGS) (CO2 + H2 → CO + H2O) catalyzed by a series of compositionally and structurally well-defined RhnVO3,4- (n = 3-7) clusters were identified under variable temperatures (298-773 K). It is discovered that the Rh5-7VO3,4- clusters can function more effectively to drive RWGS at relatively low temperatures. The experimentally observed size-dependent catalytic behavior was rationalized by quantum-chemical calculations; the framework of RhnVO3,4- is constructed by depositing the Rhn clusters on the VO3,4 "support", and a sandwiched base-acid-base [Rhout--Rhin+-VO3,4-; Rhout and Rhin represent the outer and inner Rh atoms, respectively] feature in Rh5-7VO3,4- governs the adsorption and activation of reactants as well as the facile desorption of the products. In contrast, isolated Rh5-7- clusters without the electronic modification of the VO3,4 "support" can only catalyze RWGS under relatively high-temperature conditions.

Visualizing the gas-sensitive structure of the CuZn surface in methanol synthesis catalysis

Methanol formation over Cu/ZnO catalysts is linked with a catalytically active phase created by contact between Cu nanoparticles and Zn species whose chemical and structural state depends on reaction conditions. Herein, we use variable-temperature scanning tunneling microscopy at elevated pressure conditions combined with X-ray photoelectron spectroscopy measurements to investigate the surface structures and chemical states that evolve when a CuZn/Cu(111) surface alloy is exposed to reaction gas mixtures. In CO2 hydrogenation conditions, Zn stays embedded in the CuZn surface, but once CO gas is added to the mixture, the Zn segregates onto the Cu surface. The Zn segregation is CO-induced, and establishes a new dynamic state of the catalyst surface where Zn is continually exchanged at the Cu surface. Candidates for the migrating few-atom Zn clusters are further identified in time-resolved imaging series. The findings point to a significant role of CO affecting the distribution of Zn in the multiphasic ZnO/CuZn/Cu catalysts.

In Situ Carbon-Confined MoSe2 Catalyst with Heterojunction for Highly Selective CO2 Hydrogenation to Methanol

The synthesis of methanol from CO2 hydrogenation is an effective measure to deal with global climate change and an important route for the chemical fixation of CO2. In this work, carbon-confined MoSe2 (MoSe2@C) catalysts were prepared by in situ pyrolysis using glucose as a carbon source. The physico-chemical properties and catalytic performance of CO2 hydrogenation to yield methanol were compared with MoSe2 and MoSe2/C. The results of the structure characterization showed MoSe2 displayed few layers and a small particle size. Owing to the synergistic effect of the Mo2C-MoSe2 heterojunction and in situ carbon doping, MoSe2@C with a suitable C/Mo mole ratio in the precursor showed excellent catalytic performance in the synthesis of methanol from CO2 hydrogenation. Under the optimal catalyst MoSe2@C-55, the selectivity of methanol reached 93.7% at a 9.7% conversion of CO2 under optimized reaction conditions, and its catalytic performance was maintained without deactivation during a continuous reaction of 100 h. In situ diffuse infrared Fourier transform spectroscopy studies suggested that formate and CO were the key intermediates in CO2 hydrogenation to methanol.

Biocatalysis of CO2 and CH4: Key enzymes and challenges

Mitigating greenhouse gas emissions is a critical challenge for promoting global sustainability. The utilization of CO2 and CH4 as substrates for the production of valuable products offers a promising avenue for establishing an eco-friendly economy. Biocatalysis, a sustainable process utilizing enzymes to facilitate biochemical reactions, plays a significant role in upcycling greenhouse gases. This review provides a comprehensive overview of the enzymes and associated reactions involved in the biocatalytic conversion of CO2 and CH4. Furthermore, the challenges facing the field are discussed, paving the way for future research directions focused on developing robust enzymes and systems for the efficient fixation of CO2 and CH4.

The Enigma of Methanol Synthesis by Cu/ZnO/Al2O3-Based Catalysts

The activity and durability of the Cu/ZnO/Al2O3 (CZA) catalyst formulation for methanol synthesis from CO/CO2/H2 feeds far exceed the sum of its individual components. As such, this ternary catalytic system is a prime example of synergy in catalysis, one that has been employed for the large scale commercial production of methanol since its inception in the mid 1960s with precious little alteration to its original formulation. Methanol is a key building block of the chemical industry. It is also an attractive energy storage molecule, which can also be produced from CO2 and H2 alone, making efficient use of sequestered CO2. As such, this somewhat unusual catalyst formulation has an enormous role to play in the modern chemical industry and the world of global economics, to which the correspondingly voluminous and ongoing research, which began in the 1920s, attests. Yet, despite this commercial success, and while research aimed at understanding how this formulation functions has continued throughout the decades, a comprehensive and universally agreed upon understanding of how this material achieves what it does has yet to be realized. After nigh on a century of research into CZA catalysts, the purpose of this Review is to appraise what has been achieved to date, and to show how, and how far, the field has evolved. To do so, this Review evaluates the research regarding this catalyst formulation in a chronological order and critically assesses the validity and novelty of various hypotheses and claims that have been made over the years. Ultimately, the Review attempts to derive a holistic summary of what the current body of literature tells us about the fundamental sources of the synergies at work within the CZA catalyst and, from this, suggest ways in which the field may yet be further advanced.

Boosted Sacrificial-Agent-Free Selective Photoreduction of CO2 to CH3OH by Rhenium Atomically Dispersed on Indium Oxide

Solar-energy-driven photoreduction of CO2 is promising in alleviating environment burden, but suffers from low efficiency and over-reliance on sacrificial agents. Herein, rhenium (Re) is atomically dispersed in In2O3 to fabricate a 2Re-In2O3 photocatalyst. In sacrificial-agent-free photoreduction of CO2 with H2O, 2Re-In2O3 shows a long-term stable efficiency which is enhanced by 3.5 times than that of pure In2O3 and is also higher than those on Au-In2O3, Ag-In2O3, Cu-In2O3, Ir-In2O3, Ru-In2O3, Rh-In2O3 and Pt-In2O3 photocatalysts. Moreover, carbon-based product of the photoreduction overturns from CO on pure In2O3 to CH3OH on 2Re-In2O3. Re promotes charge separation, H2O dissociation and CO2 activation, thus enhancing photoreduction efficiency of CO2 on 2Re-In2O3. During the photoreduction, CO is a key intermediate. CO prefers to desorption rather than hydrogenation on pure In2O3, as CO binds to pure In2O3 very weakly. Re strengthens the interaction of CO with 2Re-In2O3 by 5.0 times, thus limiting CO desorption but enhancing CO hydrogenation to CH3OH. This could be the origin for photoreduction product overturn from CO on pure In2O3 to CH3OH on 2Re-In2O3. The present work opens a new way to boost sacrificial-agent-free photoreduction of CO2.

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.

Electrochemically coupled CH4 and CO2 consumption driven by microbial processes

The chemical transformations of methane (CH4) and carbon dioxide (CO2) greenhouse gases typically have high energy barriers. Here we present an approach of strategic coupling of CH4 oxidation and CO2 reduction in a switched microbial process governed by redox cycling of iron minerals under temperate conditions. The presence of iron minerals leads to an obvious enhancement of carbon fixation, with the minerals acting as the electron acceptor for CH4 oxidation and the electron donor for CO2 reduction, facilitated by changes in the mineral structure. The electron flow between the two functionally active microbial consortia is tracked through electrochemistry, and the energy metabolism in these consortia is predicted at the genetic level. This study offers a promising strategy for the removal of CH4 and CO2 in the natural environment and proposes an engineering technique for the utilization of major greenhouse gases.

Copper Single Atoms Chelated on Ligand-Modified Carbon for Ullmann-type C-O Coupling

Cross-coupling reactions are of great importance in chemistry due to their ability to facilitate the construction of complex organic molecules. Among these reactions, the Ullmann-type C-O coupling between phenols and aryl halides is particularly noteworthy and useful for preparing diarylethers. However, this reaction typically relies on homogeneous catalysts that rapidly deactivate under harsh reaction conditions. In this study, we introduce a novel heterogeneous catalyst for the Ullmann-type C-O coupling reaction, comprised of isolated Cu atoms chelated to a tetraethylenepentamine-pyrrole ligand that is immobilized on graphite nanoplatelets. The catalytic study reveals the recyclability of the material, and demonstrates the crucial role of the pyrrole linker in stabilizing the Cu sites. The work expands the potential of single-atom catalyst nanoarchitectures and underscores the significance of ligands in stabilizing metals in cationic forms, providing a novel, tailored catalyst for cross-coupling chemistries.

Strategies to improve hydrogen activation on gold catalysts

Catalytic reactions involving molecular hydrogen are at the heart of many transformations in the chemical industry. Classically, hydrogenations are carried out on Pd, Pt, Ru or Ni catalysts. However, the use of supported Au catalysts has garnered attention in recent years owing to their exceptional selectivity in hydrogenation reactions. This is despite the limited understanding of the physicochemical aspects of hydrogen activation and reaction on Au surfaces. A rational design of new improved catalysts relies on making better use of the hydrogenating properties of Au. This Review analyses the strategies utilized to improve hydrogen-Au interactions, from addressing the importance of the Au particle size to exploring alternative mechanisms for H2 dissociation on Au cations and Au-ligand interfaces. These insights hold the potential to drive future applications of Au catalysis.