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Reaction mechanism studies. In situ DRIFTS spectra on K-Co 2 C for (A) CO 2 pre-adsorption. (B) Intermediates conversion with switching to H 2 at 260°C, 1.2 MPa. (C) Evolution of surface species according to the intensity of infrared featured bands.
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The decomposition of cobalt carbide (Co2C) to metallic cobalt in CO2 hydrogenation results in a notable drop in the selectivity of valued C2+ products, and the stabilization of Co2C remains a grand challenge. Here, we report an in situ synthesized K-Co2C catalyst, and the selectivity of C2+ hydrocarbons in CO2 hydrogenation achieves 67.3% at 300°C,...
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... nm, beyond the sensitive size range in CO 2 hydrogenation) and morphology of Co 3 O 4 with the K modification (fig. S2). The particle size of K-Co 3 O 4 exhibits a narrower distribution owing to the secondary calcination. Energy-dispersive spectroscopy (EDS) mappings confirm that the K promoter is uniformly dispersed across the Co 3 O 4 surface ( fig. S3). These precursors were used in CO 2 hydrogenation reaction at 300°C, 3.0 MPa with a space velocity of 6000 ml g −1 hour −1 . We collected the spent samples, which were tested for 3 hours of CO 2 hydrogenation, after careful passivation. The characteristic XRD peaks for spent samples derived from Co 3 O 4 and K-Co 3 O 4 are assigned to ...
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... conversion, can create a relatively C-rich and H-lean environment, inhibiting the deep hydrogenation while promoting the C─C coupling (37). In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was carried out to gain insight into the reaction pathways, and the detailed peak assignments are listed in table S5. As shown in Fig. 3A, the spectra for CO 2 pre-adsorbed on K-Co 2 C were collected during the pressurization of CO 2 to 1.2 MPa at 50°C and subsequent heating to 260°C. CO 2 was initially activated as monodentate carbonate (m-CO 3 2− , at 1511, 1437, 1395, and 1278 cm −1 ) and bidentate carbonate (b-CO 3 2− , at 1676 and 1625 cm −1 ) on the K-Co 2 C ...
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... 0.5%, the features of deactivation are quite similar. Furthermore, without co-feeding H 2 O, the decrease of the activity (31.6 to 24.2%) and selectivity alterations were clearly observed in 35 to 50 hours, while final CH 4 selectivity increased to 74.7% and the STY of C 2+ HCs dropped from 7.6 to 2.6 mmol g −1 hour −1 within 50 hours on stream ( fig. S33). By comparison, with co-feeding 0.5% H 2 O (Fig. 6D), the K-Co 2 C catalyst showed higher stability throughout a 210-hour test. The final selectivity to C 2+ HCs remained at 49.2%, exceeding 90% of the initial values (53.0%, at 15 hours), and the STY of C 2+ HCs still retained 7.2 mmol g −1 hour −1 at 210 hours. The XRD patterns of ...
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... By comparison, with co-feeding 0.5% H 2 O (Fig. 6D), the K-Co 2 C catalyst showed higher stability throughout a 210-hour test. The final selectivity to C 2+ HCs remained at 49.2%, exceeding 90% of the initial values (53.0%, at 15 hours), and the STY of C 2+ HCs still retained 7.2 mmol g −1 hour −1 at 210 hours. The XRD patterns of spent samples ( fig. S34) show that co-feeding 25% H 2 O caused the complete decomposition of Co 2 C, which is in accordance with the in situ XRD results (Fig. 4E). However, no substantial difference was observed in spent samples with cofeeding 0.5 or 2.5% H 2 O, indicating that their evolution mainly occurs on the catalytic surface. The quasi in situ XPS ...
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... the reaction chamber equipped with the NAP-XPS system. Here, these quasi in situ XPS spectra were recorded after reaching the setting temperatures for 20 min. The thermal couples were placed at the side of the powder sample for in situ XRD (set temperature, ±30°C) and on the upper surface of the sample piece for quasi in stu XPS, respectively ( fig. ...
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... N 2 purge for at least 1 hour. The flow rate of reactive gas (CO 2 /H 2 /N 2 = 21:63:16) or N 2 is 30 ml min −1 , whereas that of CO 2 , CO, or H 2 is 10 ml min −1 . As for mechanism studies on K-Co 2 C and Co 0 -t samples, the testing temperature is not above 260°C for avoiding the destroy from CO 2 or H 2 on catalyst structure. As shown in fig. S36, these samples were in situ synthesized in the IR cell at 300°C, 1.2 MPa for 3 hours, and then was purged (300°C) and cooled (50°C) in N 2 , atmospheric pressure before the adsorption of CO 2 and the following switching to H 2 . The co-fed H 2 O at atmospheric pressure for in situ XRD or DRIFTS and quasi in situ XPS test is stored in a ...
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... in a glass wash bottle, which is placed before the reactor chamber. Its content is dependent on the controlled temperature of wash bottle. The theoretical H 2 O content was calculated according to the following equation and was used for the expression. The actual H 2 O content was determined using the NaOH and silica gel as the absorbents ( fig. S37), while the above results are listed in table ...
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... (20 to 40 meshes), and then loaded into the middle of the reactor. Catalytic performance was tested in the reactive gas (CO 2 /H 2 /Ar = 1:3:1.5, space velocity = 6000 ml g −1 hour −1 , P = 3.0 MPa unless otherwise noted) at 260°, 300°, and 340°C. The products were collected at about 3 hours after reaching the steady state on steam. As shown in fig. S38, all the products, including the liquid oxygenates and C 5+ HCs, were heated by an oven and heating belt at 100°C for full vaporization and accessed into the online chromatography (Agilent, 7890B) for the analysis by the thermal conductivity detector and flame ionization detector, while the Ar was used as an internal standard. CO 2 ...
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We herein report a novel Mn-SNS-based catalyst, which is capable of performing indirect hydrogenation of CO2 to methanol via formylation. In this domain of CO2 hydrogenation, pincer ligands have shown a clear predominance. Our catalyst is based on the SNS-type tridentate ligand, which is quite stable and cheap as compared to the pincer type ligands...
Citations
... The broad Anderson-Schulz-Flory (ASF) distribution poses challenge as it restricts selectivity to the intended hydrocarbon fraction. Many efforts have been made to improve the activity and olefin selectivity by tuning the support [11,12], catalyst promotion [13,14], catalytic reactor optimization [15] and refinement of reaction conditions [16]. ...
Fischer-Tropsch synthesis (FTS) converts syngas into multi-carbon products, whose distribution is highly dependent on the catalyst structure. Here, nano-iron catalysts with different silica supports were prepared, and their activities and durability for Fischer-Tropsch to olefins (FTO) process were investigated. Fe/KCC-1 demonstrated the best FTO catalytic selectivity of 25.0% for C2–4= and an olefin-to-paraffin ratio of 1.68. Its open pore structure allowed primary olefins to escape quickly from the catalyst surface, lowering the probability for secondary reactions. However, its durability was lower than Fe/SBA-15 due to coke formation, pore structure collapse and Fe particle agglomeration. The thermal stability of SBA-15 resulted in its better durability, and the encapsulated Fe particles inside the cylindrical mesopores also allowed better resistance to sintering. However, the less open structure of Fe/SBA-15 led to longer residence time for the primary olefins and increased possibility for secondary reactions, causing undesired chain growth.
Graphical Abstract
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.
Reconstruction of supported nanocatalysts often occurs in gas–solid reactions and significantly affects the catalytic performance, yet it is much less explored in liquid-phase environment. Herein, we find that highly-dispersed Ag nanocatalysts, i.e., AgOx clusters, supported on alumina, silica, and titania, can aggregate into larger Ag or Ag2O particles after immersing in liquid-phase media at room temperature. The spontaneous aggregation of AgOx clusters in liquid water is attributed to liquid-phase Ostwald ripening through dissolution of AgOx clusters into water and subsequent redeposition to form Ag2O particles. The immersion into organic solvents such as ethanol leads to reduction of AgOx clusters and further growth into Ag particles. This work reveals that liquid-phase reaction media can induce substantial structural evolution of supported nanostructured catalysts, which should be carefully considered in liquid–solid interface catalytic reactions such as electrocatalysis, environmental catalysis, and organic synthesis in liquid phase.
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.
Thermocatalytic CO2 hydrogenation to liquid fuels, including ethanol and liquid hydrocarbons, has drawn global attention recently as a potential strategy to decrease CO2 emissions and reduce the consumption of and dependence on fossil fuels. The nature of catalyst has an important impact on the conversion and selectivity and clarifying the catalyst structure-performance relationship is essential to synthesize the desired liquid products. Compared with C1 products, the generation of ethanol and liquid hydrocarbons with two or more carbon atoms is more difficult owing to the high energy barrier for C–C coupling. Current studies show that the interfacial catalysts are suitable for CO2 hydrogenation to ethanol and the active interface is generally responsible for key CO* insertion, while the metal/carbide catalysts and oxide-zeolite tandem catalysts play vital roles in that to liquid hydrocarbons. In this chapter, we discuss the latest advances in the representative noble metals, transition metals and their carbides, and modified Cu-based catalysts for the synthesis of ethanol, Fe–, Co-based catalysts as well as tandem catalysts for that of long-chain hydrocarbons. Fundamental understanding on active sites, structural evolution, CO2 activation, and reaction mechanism are discussed based on computational and experimental results. On this basis, we discuss some concepts on catalyst design as well as the challenges and opportunities for its development and potential industrial applications.
Developing inexpensive cobalt-based catalysts with sufficiently high activity and selectivity for heterogeneous hydroformylation has aroused great interest but remains challenging. Herein, a series of K-promoted Co/SiO2 catalysts were synthesized and...
