Unravelling the Promotional Effect of La2O3 in Pt/La-TiO2 Catalysts for CO2 Hydrogenation

This work reports the preparation of a La₂O₃-modified Pt/TiO₂ (Pt/La-TiO₂) hybrid through an excess-solution impregnation method and its application for CO₂ hydrogenation catalysis. The Pt/La-TiO₂ catalyst is characterized by XRD, H₂ temperature-programmed reduction (TPR), TEM, X-ray photoelectron spectroscopy (XPS), Raman, EPR, and N₂ sorption measurements. The Pt/La-TiO₂ composite starts to catalyze the CO₂ conversion reaction at 220 °C, which is 30 °C lower than the Pt/TiO₂ catalyst. The generation of CH₄ and CO of Pt/La-TiO₂ is 1.6 and 1.4 times greater than that of Pt/TiO₂. The CO₂ temperature-programmed desorption (TPD) analysis confirms the strengthened CO₂ adsorption on Pt/La-TiO₂. Moreover, the in situ FTIR experiments demonstrate that the enhanced CO₂ adsorption of Pt/La-TiO₂ facilitates the formation of the active Pt–CO intermediate and subsequently boosts the evolution of CH₄ and CO. The cycling tests reveal that Pt/La-TiO₂ shows reinforced stability for the CO₂ hydrogenation reaction because the La species can prevent Pt nanoparticles (NPs) from sintering. This work may provide some guidance on the development new rare-metal-modified hybrid catalysts for CO₂ fixation.     

Pivotal Role of Holes in Photocatalytic CO2 Reduction on TiO2

Evidence is provided that in a gas-solid photocatalytic reaction the removal of photogenerated holes from a titania (TiO₂) photocatalyst is always detrimental for photocatalytic CO₂ reduction. The coupling of the reaction to a sacrificial oxidation reaction hinders or entirely prohibits the formation of CH₄ as a reduction product. This agrees with earlier work in which the detrimental effect of oxygen-evolving cocatalysts was demonstrated. Photocatalytic alcohol oxidation or even overall water splitting proceeds in these reaction systems, but carbon-containing products from CO₂ reduction are no longer observed. H₂ addition is also detrimental, either because it scavenges holes or because it is not an efficient proton donor on TiO₂. The results are discussed in light of previously suggested reaction mechanisms for photocatalytic CO₂ reduction. The formation of CH₄ from CO₂ is likely not a linear sequence of reduction steps but includes oxidative elementary steps. Furthermore, new hypotheses on the origin of the required protons are suggested.     

Ceria-Supported Cobalt Catalyst for Low-Temperature Methanation at Low Partial Pressures of CO2

The direct catalytic conversion of atmospheric CO₂ to valuable chemicals is a promising solution to avert negative consequences of rising CO₂ concentration. However, heterogeneous catalysts efficient at low partial pressures of CO₂ still need to be developed. Here, we explore Co/CeO₂ as a catalyst for the methanation of diluted CO₂ streams. This material displays an excellent performance at reaction temperatures as low as 175 °C and CO₂ partial pressures as low as 0.4 mbar (the atmospheric CO₂ concentration). To gain mechanistic understanding of this unusual activity, we employed in situ X-ray photoelectron spectroscopy and operando infrared spectroscopy. The higher surface concentration and reactivity of formates and carbonyls—key reaction intermediates—explain the superior activity of Co/CeO₂ as compared to a conventional Co/SiO₂ catalyst. This work emphasizes the catalytic role of the cobalt-ceria interface and will aid in developing more efficient CO₂ hydrogenation catalysts.     

Surface and Interface Engineering for the Catalysts of Electrocatalytic CO2 Reduction

The massive use of fossil fuels releases a great amount of CO₂, which substantially contributes to the global warming. For the global goal of putting CO₂ emission under control, effective utilization of CO₂ is particularly meaningful. Electrocatalytic CO₂ reduction reaction (eCO₂RR) has great potential in CO₂ utilization, because it can convert CO₂ into valuable carbon-containing chemicals and feedstock using renewable electricity. The catalyst design for eCO₂RR is a key challenge to achieving efficient conversion of CO₂ to fuels and useful chemicals. For a typical heterogeneous catalyst, surface and interface engineering is an effective approach to enhance reaction activity. Herein, the development and research progress in CO₂ catalysts with focus on surface and interface engineering are reviewed. First, the fundaments of eCO₂RR is briefly discussed from the reaction mechanism to performance evaluation methods, introducing the role of the surface and interface engineering of electrocatalyst in eCO₂RR. Then, several routes to optimize the surface and interface of CO₂ electrocatalysts, including morphology, dopants, atomic vacancies, grain boundaries, surface modification, etc., are reviewed and representative examples are given. At the end of this review, we share our personal views in future research of eCO₂RR.     

Electrolyte Effects on the Electrochemical Reduction of CO2

The electrochemical reduction of CO₂ to fuels or commodity chemicals is a reaction of high interest for closing the anthropogenic carbon cycle. The role of the electrolyte is of particular interest, as the interplay between the electrocatalytic surface and the electrolyte plays an important role in determining the outcome of the CO₂ reduction reaction. Therefore, insights on electrolyte effects on the electrochemical reduction of CO₂ are pivotal in designing electrochemical devices that are able to efficiently and selectively convert CO₂ into valuable products. Here, we provide an overview of recently obtained insights on electrolyte effects and we discuss how these insights can be used as design parameters for the construction of new electrocatalytic systems.     

CO2 Reduction Mechanism on the Cu2O(110) Surface: A First-Principles Study

Cu₂O is an attractive catalyst for the selective reduction of CO₂ to methanol. However, the mechanism of the reaction and the role of the Cu species in different oxidation states are not well understood yet. In this work, by first-principles calculations, we investigate the mechanism of the reaction on the Cu₂O(110) surface, which is the most selective for methanol, in different degrees of reduction: ideal surface, slightly reduced surface (SRS), and partially reduced surface (PRS). The most favorable reaction pathways on the three surfaces were identified. We found that Cu(I) on the ideal surface is not capable of chemisorbing CO₂, but surface oxygen serves as the active site which selectively converts CO₂ to CH₃OH with a limiting potential of −0.77 V. The Cu(0) on the SRS and PRS promotes the adsorption and reduction of CO₂, while the removal of the residue O* becomes potential/rate limiting with a more negative limiting potential than the ideal surface. The SRS is selective to methanol while the PRS becomes selective to methane. The result suggests that the key to high methanol selectivity is to avoid the reduction of Cu(I), which provides a new strategy for the design of more efficient catalysts for selective CO₂ reduction to methanol.     

A New Type of Photocatalysis Initiated by Photoexcitation of Adsorbed Carbon Dioxide on ZrO2

ZrO₂ has been found to be an effective photocatalyst for reduction of CO₂ by hydrogen or methane at room temperature. The effective photon energy is less than the band gap energy of ZrO₂ (5.0 eV), indicating that photoexcitation of bulk ZrO₂ is not involved. The reaction is initiated by photoexcitation of surface carbonates derived from adsorption of CO₂ to convert it to a CO₂ ^– radical, which in turn reacts with hydrogen or methane to form surface formate. The formate is stable at temperatures below 573 K, but works as a reductant of CO₂ under photoirradiation. A new type of reaction mechanism is proposed.     

Designs of Tandem Catalysts and Cascade Catalytic Systems for CO2 Upgrading

Upgrading CO₂ into multi-carbon (C2+) compounds through the CO₂ reduction reaction (CO₂RR) offers a practical approach to mitigate atmospheric CO₂ while simultaneously producing high value chemicals. The reaction pathways for C2+ production involve multi-step proton-coupled electron transfer (PCET) and C−C coupling processes. By increasing the surface coverage of adsorbed protons (*H_ad) and *CO intermediates, the reaction kinetics of PCET and C−C coupling can be accelerated, thereby promoting C2+ production. However, *H_ad and *CO are competitively adsorbed intermediates on monocomponent catalysts, making it difficult to break the linear scaling relationship between the adsorption energies of the *H_ad/*CO intermediate. Recently, tandem catalysts consisting of multicomponents have been developed to improve the surface coverage of *H_ad or *CO by enhancing water dissociation or CO₂-to-CO production on auxiliary sites. In this context, we provide a comprehensive overview of the design principles of tandem catalysts based on reaction pathways for C2+ products. Moreover, the development of cascade CO₂RR catalytic systems that integrate CO₂RR with downstream catalysis has expanded the range of potential CO₂ upgrading products. Therefore, we also discuss recent advancements in cascade CO₂RR catalytic systems, highlighting the challenges and perspectives in these systems.     

Aktivierung von CO2 an Übergangsmetallzentren: Zum Ablauf der CO2-Reduktion an Nickel(0)-Fragmenten

Activation of CO₂ at Transition Metal Centres: The Route of the CO₂ Reduction at Nikel(0) Moieties A competing reaction in the catalytic cyclooligomerization of hex-3-yne and CO₂ at the (TMED)Ni(0)-fragment (TMED = N,N,N′,N′-tetramethylethylendiamine) is the formation of carbon monoxide and (TMED)Ni(CO₃). So it is possible to explain the generation of II (TMED)Ni(diethylmalicacidanhydride) and III (a nickel trimer with two (TMED)Ni(CO₃) units). Both complexes are characterized by X-ray analysis. The reduction of CO₂ to CO most likely proceeds via an intermediate in which two molecules of carbon dioxide are coupled head-to-tail to form a metallacycle. An ab initio scf geometry optimization supports the existence of such an intermediate.     

Efficient Electrochemical Reduction of CO2 to HCOOH over Sub‐2 nm SnO2 Quantum Wires with Exposed Grain Boundaries

Electrochemical reduction of CO₂ could mitigate environmental problems originating from CO₂ emission. Although grain boundaries (GBs) have been tailored to tune binding energies of reaction intermediates and consequently accelerate the CO₂ reduction reaction (CO₂RR), it is challenging to exclusively clarify the correlation between GBs and enhanced reactivity in nanostructured materials with small dimension (<10 nm). Now, sub‐2 nm SnO₂ quantum wires (QWs) composed of individual quantum dots (QDs) and numerous GBs on the surface were synthesized and examined for CO₂RR toward HCOOH formation. In contrast to SnO₂ nanoparticles (NPs) with a larger electrochemically active surface area (ECSA), the ultrathin SnO₂ QWs with exposed GBs show enhanced current density (j), an improved Faradaic efficiency (FE) of over 80 % for HCOOH and ca. 90 % for C1 products as well as energy efficiency (EE) of over 50 % in a wide potential window; maximum values of FE (87.3 %) and EE (52.7 %) are achieved.     

Comprehensive Mechanism of CO2 Electroreduction on Non-Noble Metal Single-Atom Catalysts of Mo2CS2-MXene

In this work, a series of non-noble metal single-atom catalysts of Mo₂CS₂-MXene for CO₂ reduction were systematically investigated by well-defined density-functional-theory (DFT) calculations. It is found that nine types of transitional metal (TM) supported Mo₂CS₂ (TM-Mo₂CS₂) are very stable, while eight can effectively inhibit the competitive hydrogen evolution reaction (HER). After comprehensively comparing the changes of free energy for each pathway in CO₂ reduction reaction (CO₂RR), it is found that the products of TM-Mo₂CS₂ are not completely CH₄. Furthermore, Cr-, Fe-, Co- and Ni-Mo₂CS₂ are found to render excellent CO₂RR catalytic activity, and their limiting potentials are in the range of 0.245–0.304 V. In particular, Fe-Mo₂CS₂ with a nitrogenase-like structure has the lowest limiting potential and the highest electrocatalytic activity. Ab initio molecular dynamics (AIMD) simulations have also proven that these kinds of single-atom catalysts with robust performance could exist stably at room temperature. Therefore, these single TM atoms anchored on the surface of MXenes can be profiled as a promising catalyst for the electrochemical reduction of CO₂.     

Kinetic study of CO2 absorption in aqueous solutions of 2-((2-aminoethyl)amino)-ethanol using a stirred cell reaction calorimeter

In the literature, aqueous 2-((2-aminoethyl)amino) ethanol (AEEA) is identified as a promising solvent for postcombustion CO₂ capture. In this work, the kinetics of CO₂ absorption in the aqueous AEEA, containing a primary and a secondary amino group, is studied over a wide temperature range of 303.15-343.15 K and the amine concentration in the range of 0.47-2.89 M using the fall-in-pressure technique in a stirred cell reaction calorimeter setup with a horizontal gas-liquid interface. The overall rate constants for (AEEA + H₂O + CO₂) reaction system are estimated in the pseudo–first-order reaction regime. The kinetic models based on zwitterion and the termolecular reaction mechanisms are used to predict kinetic rate constants. The experimental kinetic data are better correlated using the zwitterion mechanism (AAD 9.18%) than that of the termolecular mechanism (AAD 10.4%). The density, viscosity, and physical solubility of pure components and aqueous binary mixtures of AEEA are also measured at the similar temperature and concentration ranges of rate kinetics. Empirical models are proposed to predict pure component density and viscosity data with AAD of 0.02% and 7.17%, respectively. The Redlich-Kister model, the Grunberg-Nissan model, and the O'Connell's model are used to correlate experimental density, viscosity, and physical solubility data of the binary mixtures with AAD of 0.034%, 4.92%, and 6.5%, respectively. The reaction activation energy (E_a ∼ 32 kJ/mol) of the (AEEA + H₂O + CO₂) system is calculated from the Arrhenius power-law model using the zwitterion mechanism, which indicates lower energy barrier than that of the reported value for monoethanolamine (∼44 kJ/mol) in the literature.     

Significant Acceleration of Photocatalytic CO2 Reduction at the Gas-Liquid Interface of Microdroplets**

Solar-driven CO₂ reduction reaction (CO₂RR) is largely constrained by the sluggish mass transfer and fast combination of photogenerated charge carriers. Herein, we find that the photocatalytic CO₂RR efficiency at the abundant gas-liquid interface provided by microdroplets is two orders of magnitude higher than that of the corresponding bulk phase reaction. Even in the absence of sacrificial agents, the production rates of HCOOH over WO₃ ⋅ 0.33H₂O mediated by microdroplets reaches 2536 μmol h⁻¹ g⁻¹ (vs. 13 μmol h⁻¹ g⁻¹ in bulk phase), which is significantly superior to the previously reported photocatalytic CO₂RR in bulk phase reaction condition. Beyond the efficient delivery of CO₂ to photocatalyst surfaces within microdroplets, we reveal that the strong electric field at the gas-liquid interface of microdroplets essentially promotes the separation of photogenerated electron-hole pairs. This study provides a deep understanding of ultrafast reaction kinetics promoted by the gas-liquid interface of microdroplets and a novel way of addressing the low efficiency of photocatalytic CO₂ reduction to fuel.     

CO2 Electroreduction in Ionic Liquids: A Review

The increasing emission of carbon dioxide (CO₂) caused by the unrestrained consumption of fossil fuels in recent hundreds of years, has caused global environmental and social problems. Meanwhile, CO₂ is a cheap, abundant and renewable C1‐feedstock, which can be converted into alcohols, ethers, acids and other value‐added chemicals. Compared with the thermal reactions, electrochemical reduction of CO₂ is more attractive because of its advantages by using the seasonal, geographical and intermittent energy (tide, wind and solar) under mild conditions. In recent years, taking ionic liquids (ILs) as electrolytes in the CO₂ electrochemical reduction reaction has been paid much more attention due to the advantages of lowering the overpotential of CO₂ electroreduction and improving the Faradaic efficiency. In this paper, we summarized the recent progresses of electrochemical reduction of CO₂ in ILs electrolytes, and analyzed the reaction mechanism of CO₂ reaction in the electrode‐electrolyte interface region by experimental and simulation methods. Finally, the research which needs to be highlighted in this area was proposed.     

An FTIR spectroscopic study and quantification of 2-amino-2-methyl-1-propanol,piperazine and absorbed carbon dioxide in concentrated aqueous solutions

This study reports the investigation of carbon dioxide (CO₂) absorption into an amine blend solution of 2-amino-2-methyl-1-propanol (AMP) and piperazine (PZ). The reaction in the liquid phase between CO₂ and the amines were qualitatively and quantitatively monitored by Fourier Transform Mid-Infrared spectroscopy (mid-FTIR). A multivariate partial least square regression (PLS2) model was obtained to quantify free or non-reacted AMP and PZ and absorbed CO₂ in all chemical forms, i.e. no differentiation was made into carbonates or carbamates. The calibration model was constructed using a single wide region and 270 calibration samples. The concentration of AMP, PZ and CO₂ from 568 samples were simultaneously predicted with low relative errors.     

Acetamide Electrosynthesis from CO2 and Nitrite in Water

Renewable electricity driven electrocatalytic CO₂ reduction reaction (CO₂RR) is a promising solution to carbon neutralization, which mainly generate simple carbon products. It is of great importance to produce more valuable C−N chemicals from CO₂ and nitrogen species. However, it is challenging to co-reduce CO₂ and NO₃⁻/NO₂⁻ to generate aldoxime an important intermediate in the electrocatalytic C−N coupling process. Herein, we report the successful electrochemical conversion of CO₂ and NO₂⁻ to acetamide for the first time over copper catalysts under alkaline condition through a gas diffusion electrode. Operando spectroelectrochemical characterizations and DFT calculations, suggest acetaldehyde and hydroxylamine identified as key intermediates undergo a nucleophilic addition reaction to produce acetaldoxime, which is then dehydrated to acetonitrile and followed by hydrolysis to give acetamide under highly local alkaline environment and electric field. Moreover, the above mechanism was successfully extended to the formation of phenylacetamide. This study provides a new strategy to synthesize highly valued amides from CO₂ and wastewater.     

Simultaneous co-Photocatalytic CO2 Reduction and Ethanol Oxidation towards Synergistic Acetaldehyde Synthesis

Photocatalytic conversion of CO₂ is of great interest but it often suffers sluggish oxidation half reaction and undesired by-products. Here, we report for the first the simultaneous co-photocatalytic CO₂ reduction and ethanol oxidation towards one identical value-added CH₃CHO product on a rubidium and potassium co-modified carbon nitride (CN-KRb). The CN-KRb offers a record photocatalytic activity of 1212.3 μmol h⁻¹g⁻¹ with a high selectivity of 93.3 % for CH₃CHO production, outperforming all the state-of-art CO₂ photocatalysts. It is disclosed that the introduced Rb boosts the *OHCCHO fromation and facilitates the CH₃CHO desorption, while K promotes ethanol adsorption and activation. Moreover, the H⁺ stemming from ethanol oxidation is confirmed to participate in the CO₂ reduction process, endowing near ideal overall atomic economy. This work provides a new strategy for effective use of the photoexcited electron and hole for high selective and sustainable conversion of CO₂ paired with oxidation reaction into identical product.     

Engineering a Copper Single-Atom Electron Bridge to Achieve Efficient Photocatalytic CO2 Conversion

Developing highly efficient and stable photocatalysts for the CO₂ reduction reaction (CO₂RR) remains a great challenge. We designed a Z-Scheme photocatalyst with N−Cu₁−S single-atom electron bridge (denoted as Cu-SAEB), which was used to mediate the CO₂RR. The production of CO and O₂ over Cu-SAEB is as high as 236.0 and 120.1 μmol g⁻¹ h⁻¹ in the absence of sacrificial agents, respectively, outperforming most previously reported photocatalysts. Notably, the as-designed Cu-SAEB is highly stable throughout 30 reaction cycles, totaling 300 h, owing to the strengthened contact interface of Cu-SAEB, and mediated by the N−Cu₁−S atomic structure. Experimental and theoretical calculations indicated that the SAEB greatly promoted the Z-scheme interfacial charge-transport process, thus leading to great enhancement of the photocatalytic CO₂RR of Cu-SAEB. This work represents a promising platform for the development of highly efficient and stable photocatalysts that have potential in CO₂ conversion applications.     

Catholyte‐Free Electrocatalytic CO2 Reduction to Formate

Electrochemical reduction of carbon dioxide (CO₂) into value‐added chemicals is a promising strategy to reduce CO₂ emission and mitigate climate change. One of the most serious problems in electrocatalytic CO₂ reduction (CO₂R) is the low solubility of CO₂ in an aqueous electrolyte, which significantly limits the cathodic reaction rate. This paper proposes a facile method of catholyte‐free electrocatalytic CO₂ reduction to avoid the solubility limitation using commercial tin nanoparticles as a cathode catalyst. Interestingly, as the reaction temperature rises from 303 K to 363 K, the partial current density (PCD) of formate improves more than two times with 52.9 mA cm^?2, despite the decrease in CO₂ solubility. Furthermore, a significantly high formate concentration of 41.5 g L^?1 is obtained as a one‐path product at 343 K with high PCD (51.7 mA cm^?2) and high Faradaic efficiency (93.3 %) via continuous operation in a full flow cell at a low cell voltage of 2.2 V.     

Highly Efficient CO2 Utilization via Aqueous Zinc– or Aluminum–CO2 Systems for Hydrogen Gas Evolution and Electricity Production

Atmospheric carbon dioxide (CO₂) has increased from 278 to 408 parts per million (ppm) over the industrial period and has critically impacted climate change. In response to this crisis, carbon capture, utilization, and storage/sequestration technologies have been studied. So far, however, the economic feasibility of the existing conversion technologies is still inadequate owing to sluggish CO₂ conversion. Herein, we report an aqueous zinc– and aluminum–CO₂ system that utilizes acidity from spontaneous dissolution of CO₂ in aqueous solution to generate electrical energy and hydrogen (H₂). The system has a positively shifted onset potential of hydrogen evolution reaction (HER) by 0.4 V compared to a typical HER under alkaline conditions and facile HER kinetics with low Tafel slope of 34 mV dec^?1. The Al–CO₂ system has a maximum power density of 125 mW cm^?2 which is the highest value among CO₂ utilization electrochemical system.