Stabilizing Co2C with H2O and K promoter for CO2 hydrogenation to C2+ hydrocarbons

Ru-Co Interface Unlocks Efficient Solar-Driven CO2 Conversion into Value-Added Hydrocarbons under Mild Conditions

Co-based catalysts exhibit high activity for C-C coupling in the Fischer-Tropsch synthesis unit, however, they tend to produce primarily C1 hydrocarbons (CO or CH4) during CO2 hydrogenation. Here, a novel 0.04RuCo/MnO-500 catalyst for photothermocatalytic CO2 hydrogenation, exhibiting a CO2 conversion of 65.6% and a value-added hydrocarbons (C2+) selectivity of 63.2% (excluding CO) under mild conditions is reported. The time-yield of C2+ hydrocarbons over 0.04RuCo/MnO-500 catalyst reaches 8.2 mmolCH2 gcat -1 h-1, which is 3.0-fold and 3.3-fold higher than that of Co/MnO-500 (2.7 mmolCH2 gcat -1 h-1) and 0.04Ru/MnO-500 (2.5 mmolCH2 gcat -1 h-1), respectively. Further investigations disentangle the exceptional performance that should be attributed to the interface sites between Co and Ru within the catalyst. The presence of interfacial sites enhances the ability of the catalyst to adsorb and activate intermediate (*CO) produced during CO2 hydrogenation, achieving low CO selectivity and promoting the production of value-added hydrocarbons with high CO2 conversion. This work presents a novel approach to developing the Ru/Co catalyst for directly converting CO2 into value-added hydrocarbons through photothermocatalytic hydrogenation, realizing the demand for sustainable energy sources.

Unlocking the Potential of Oxide-Based Catalysts for CO2 Photo-Hydrogenation: Oxygen Vacancies Promoted C─O Bond Cleavage in Key Intermediates

Oxygen vacancies are generally recognized to play significant roles in CO2 adsorption and activation during CO2 hydrogenation. However, by revisiting its structural/electronic affinity for a range of oxygen-containing intermediates in CO2 hydrogenation processes, the additional roles of oxygen vacancies can be long overlooked and underestimated. Herein, using CO2 (photo-)methanation as a model reaction, Co3O4 with abundant oxygen vacancies is employed to investigate the relationship between oxygen vacancies and the formation/conversion of oxygen-containing intermediates. Combined analyses of in situ diffuse reflectance infrared Fourier transform spectroscopy and theoretical calculations reveal that the key intermediate is formate, whose C─O bond cleavage is inferred to be the rate-limiting step during CO2 methanation on Co3O4. Remarkably, leveraging the oxygen vacancy-mediated C─O bond scission to accelerate the conversion of formate, the CH4 production activity (1108.1 mmol g-1 h-1) and selectivity (93%) are improved significantly. This comprehensive study provides valuable insights into the multifaceted roles of oxygen vacancies in CO2 hydrogenation reactions, establishing a solid foundation toward the design and development of high-performance oxide-containing/-based catalysts for the conversion of CO2 into various valuable chemicals.

Potassium-stabilized metastable carbides and chalcogenides via surface chemical potential modulation

Metastable carbides and chalcogenides are attractive candidates for wide and promising applications. However, their inherent instability leads to synthetic difficulty and poor durability. Thus, the development of facile strategies for the controllable synthesis and stabilization of metastable carbides is still a great challenge. Here, taking metastable ɛ-Fe2C as a case study, potassium ions (K+) are theoretically predicted and experimentally reported to control the synthesis of metastable ɛ-Fe2C from an Fe2N precursor by increasing the surface carbon chemical potential (μC). The controllable synthesis and improved stability are attributed to the better-matched denitriding and carburizing rates and the impeded spillover of carbon atoms in metastable ɛ-Fe2C with high carbon contents due to the enhanced surface μC. In addition, this strategy is suitable for synthesizing metastable γ'-MoC, MoN, 1T-MoS2, 1T-MoSe2, 1T-MoSe2xTe2(1-x), and 1T-Mo1-xWxSe2, highlighting the universality of the methodology. Impressively, gram-level scalable metastable ɛ-Fe2C remains stable for more than 398 days in air. Furthermore, ɛ-Fe2C exhibits remarkable olefin selectivity and durability for more than 36 h of continuous testing. This work not only demonstrates a facile, easily scalable, and general strategy for accessing various metastable carbides and chalcogenides but also addresses the synthetic difficulty and poor durability challenge of metastable materials.

Multifunctional electrolyte additive for high power lithium metal batteries at ultra-low temperatures

Ultra-low-temperature lithium metal batteries face significant challenges, including sluggish ion transport and uncontrolled lithium dendrite formation, particularly at high power. An ideal electrolyte requires high carrier ion concentration, low viscosity, rapid de-solvation, and stable interfaces, but balancing these attributes remains a formidable task. Here, we design and synthesize a multifunctional additive, perfluoroalkylsulfonyl quaternary ammonium nitrate (PQA-NO3), which features both cationic (PQA+) and anionic (NO3-) components. PQA+ reacts in situ with lithium metal to form an inorganic-rich solid-electrolyte interphase (SEI) that enhances Li+ transport through the SEI film. NO3- creates an anion-rich, solvent-poor solvation structure, improving oxidation stability at the positive electrode/electrolyte interface and reducing Li+-solvent interactions. This allows ether-based electrolytes to achieve high voltage tolerance, increased ionic conductivity, and lower de-solvation energy barriers. The Li (40 µm)||NMC811 (3 mAh cm-2) coin cells with the developed electrolyte exhibited stable cycling at -60 °C and a 450 Wh kg-1 pouch cell retained 48.1% capacity at -85 °C, achieving a specific energy (except tabs and packing foil, same hereafter) of 171.8 Wh kg-1. Additionally, the pouch cell demonstrated a discharge rate of 3.0 C at -50 °C, reaching a specific power (except tabs and packing foil, same hereafter) of 938.5 W kg-1, indicating the electrolyte's suitability for high-rate lithium metal batteries in extreme low-temperature environments.

Hydrogenation of CO2 for sustainable fuel and chemical production

Catalytic carbon dioxide (CO2) hydrogenation is a potential route for producing sustainable fuels and chemicals, but existing catalysts need improvement. In particular, identifying active sites and understanding the interaction between components and the dynamic behavior of the participant species remain unclear. This fundamental knowledge is essential for the design of more efficient and stable catalysts. Because the nature of the active site (metal, oxide, carbide) is the main factor that determines the catalytic activity of the catalysts, this Review focuses on various types of heterogeneous catalysts that have been recently reported in the literature as efficient for CO2 conversion to C1 [carbon monoxide (CO), methanol (CH3OH), methane (CH4)], and higher hydrocarbons. We focus on establishing key connections between active-site structures and selectivity, regardless of catalyst composition.

Understanding and Tuning the Effects of H2O on Catalytic CO and CO2 Hydrogenation

Catalytic COx (CO and CO2) hydrogenation to valued chemicals is one of the promising approaches to address challenges in energy, environment, and climate change. H2O is an inevitable side product in these reactions, where its existence and effect are often ignored. In fact, H2O significantly influences the catalytic active centers, reaction mechanism, and catalytic performance, preventing us from a definitive and deep understanding on the structure-performance relationship of the authentic catalysts. It is necessary, although challenging, to clarify its effect and provide practical strategies to tune the concentration and distribution of H2O to optimize its influence. In this review, we focus on how H2O in COx hydrogenation induces the structural evolution of catalysts and assists in the catalytic processes, as well as efforts to understand the underlying mechanism. We summarize and discuss some representative tuning strategies for realizing the rapid removal or local enrichment of H2O around the catalysts, along with brief techno-economic analysis and life cycle assessment. These fundamental understandings and strategies are further extended to the reactions of CO and CO2 reduction under an external field (light, electricity, and plasma). We also present suggestions and prospects for deciphering and controlling the effect of H2O in practical applications.

Ethanol synthesis via catalytic CO2 hydrogenation over multi-elemental KFeCuZn/ZrO2 catalyst

Technological enablers that use CO2 as a feedstock to create value-added chemicals, including ethanol, have gained widespread appeal. They offer a potential solution to climate change and promote the development of a circular economy. However, the conversion of CO2 to ethanol poses significant challenges, not only because CO2 is a thermodynamically stable and chemically inert molecule but also because of the complexity of the reaction routes and uncontrollability of C-C coupling. In this study, we developed an efficient catalyst, K-Fe-Cu-Zn/ZrO2 (KFeCuZn/ZrO2), which enhances the EtOH space time yield (STYEtOH) to 5.4 mmol gcat -1 h-1, under optimized conditions (360 °C, 4 MPa, and 12 L gcat -1 h-1). Furthermore, we investigated the roles of each constituent element using in situ/operando spectroscopy such as X-ray absorption spectroscopy (XAS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). These results demonstrate that all components are necessary for efficient ethanol synthesis.

Visualizing Phase Evolution of Co2C for Efficient Fischer-Tropsch to Olefins

Cobalt carbide (Co2C) possesses high catalytic efficiency Fischer-Tropsch synthesis (FTS), while the products selectivity appears sensitive to crystallography geometry. Since the Anderson-Schulz-Flory (ASF) distribution in FTS is broken through fabricating facetted Co2C nanocrystals, yet the underlying mechanism of Co2C crystallization remains unclarified suffering from sophisticated catalyst composition involving promoter agents. Herein, the synthesis of high-purity single-crystal nanoprisms (Co2C-p) for highly efficient FTS is reported to lower olefins. Through comprehensive microstructure analysis, e.g., high-resolution TEM, in situ TEM and electron diffraction, as well as finite element simulation of gas flow field, for the first time the full roadmap of forming catalytic active cobalt carbides is disclosed, starting from reduction of Co3O4 precursor to CoO intermediate, then carburization into Co2C-s and subsequent ripening growth into Co2C-p. This gas-induced engineering of crystal phase provides a new synthesis strategy, with many new possibilities for precise design of metal-based catalyst for diverse catalytic applications.

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

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

Role of H2O in Catalytic Conversion of C1 Molecules

Due to their role in controlling global climate change, the selective conversion of C1 molecules such as CH4, CO, and CO2 has attracted widespread attention. Typically, H2O competes with the reactant molecules to adsorb on the active sites and therefore inhibits the reaction or causes catalyst deactivation. However, H2O can also participate in the catalytic conversion of C1 molecules as a reactant or a promoter. Herein, we provide a perspective on recent progress in the mechanistic studies of H2O-mediated conversion of C1 molecules. We aim to provide an in-depth and systematic understanding of H2O as a promoter, a proton-transfer agent, an oxidant, a direct source of hydrogen or oxygen, and its influence on the catalytic activity, selectivity, and stability. We also summarize strategies for modifying catalysts or catalytic microenvironments by chemical or physical means to optimize the positive effects and minimize the negative effects of H2O on the reactions of C1 molecules. Finally, we discuss challenges and opportunities in catalyst design, characterization techniques, and theoretical modeling of the H2O-mediated catalytic conversion of C1 molecules.