C2 Oxygenate Synthesis via Fischer–Tropsch Synthesis on Co2C and Co/Co2C Interface Catalysts: How To Control the Catalyst Crystal Facet for Optimal Selectivity

The Importance of Sintering-Induced Grain Boundaries in Copper Catalysis to Improve Carbon-Carbon Coupling

Syngas conversion serves as a gas-to-liquid technology to produce liquid fuels and valuable chemicals from coal, natural gas, or biomass. During syngas conversion, sintering is known to deactivate the catalyst owing to the loss of active surface area. However, the growth of nanoparticles might induce the formation of new active sites such as grain boundaries (GBs) which perform differently from the original nanoparticles. Herein, we reported a unique Cu-based catalyst, Cu nanoparticles with in situ generated GBs confined in zeolite Y (denoted as activated Cu/Y), which exhibited a high selectivity for C5+ hydrocarbons (65.3 C%) during syngas conversion. Such high selectivity for long-chain products distinguished activated Cu/Y from typical copper-based catalysts which mainly catalyze methanol synthesis. This unique performance was attributed to the GBs, while the zeolite assisted the stabilization through spatial confinement. Specifically, the GBs enabled H-assisted dissociation of CO and subsequent hydrogenation into CHx*. CHx* species not only serve as the initiator but also directly polymerize on Cu GBs, known as the carbide mechanism. Meanwhile, the synergy of GBs and their vicinal low-index facets led to the CO insertion where non-dissociative adsorbed CO on low-index facets migrated to GBs and inserted into the metal-alkyl bond for the chain growth.

Hydrogenation of CO2 into Value-added Chemicals Using Solid-Supported Catalysts

Reducing CO2 emissions is an urgent global priority. In this context, several mitigation strategies, including CO2 tax and stringent legislation, have been adopted to halt the deterioration of the natural environment. Also, carbon recycling procedures undoubtedly help reduce net emissions into the atmosphere, enhancing sustainability. Utilizing Earth's abundant CO2 to produce high-potential green chemicals and light fuels opens new avenues for the chemical industry. In this context, many attempts have been devoted to converting CO2 as a feedstock into various value-added chemicals, such as CH4 , lower methanol, light olefins, gasoline, and higher hydrocarbons, for numerous applications involving various catalytic reactions. Although several CO2 -conversion methods have been used, including electrochemical, photochemical, and biological approaches, the hydrogenation method allows the reaction to be tuned to produce the targeted compound without significantly altering infrastructure. This review discusses the numerous hydrogenation routes and their challenges, such as catalyst design, operation, and the combined art of structure-activity relationships for the various product formations.

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

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, 3.0 MPa. Experimental and theoretical results elucidate that CoO transforms to Co₂C in the reaction, while the stabilization of Co₂C is dependent on the reaction atmosphere and the K promoter. During the carburization, the K promoter and H₂O jointly assist in the formation of surface C^* species via the carboxylate intermediate, while the adsorption of C^* on CoO is enhanced by the K promoter. The lifetime of the K-Co₂C is further prolonged from 35 hours to over 200 hours by co-feeding H₂O. This work provides a fundamental understanding toward the role of H₂O in Co₂C chemistry, as well as the potential of extending its application in other reactions.

Syngas Conversion to C2 Species over WC and M/WC (M = Cu or Rh) Catalysts: Identifying the Function of Surface Termination and Supported Metal Type

Improving the selectivity and activity of C₂ species from syngas is still a challenge. In this work, catalysts with monolayer Cu or Rh supported over WC with different surface terminations (M/WC (M = Cu or Rh)) are rationally designed to facilitate C₂ species generation. The complete reaction network is analyzed by DFT calculations. Microkinetics modeling is utilized to consider the experimental reaction temperature, pressure, and the coverage of the species. The thermal stabilities of the M/WC (M = Cu or Rh) catalysts are confirmed by AIMD simulations. The results show that the surface termination and supported metal types in the M/WC (M = Cu or Rh) catalysts can alter the existence form of abundant CH_x (x = 1-3) monomer, as well as the activity and selectivity of CH_x monomer and C₂ species. Among these, only the Cu/WC-C catalyst is screened out to achieve outstanding activity and selectivity for C₂H₂ generation, attributing to that the synergistic effect of the subsurface C atoms and the surface monolayer Cu atoms presents the noble-metal-like character to promote the generation of CH_x and C₂ species. This work demonstrates a new possibility for rational construction of other catalysts with the non-noble metal supported by the metal carbide, adjusting the surface termination of metal carbide and the supported metal types can present the noble-metal-like character to tune catalytic performance of C₂ species from syngas.

Ligand regulated metal–organic frameworks for synergistic photoredox and nickel catalysis

Synergistic photoredox and nickel catalytic cross-coupling systems have created a great attraction as a promising methodology to produce the aryl C−N bonds under mild conditions as well as extreme challenge,...

Cobalt Carbide Nanocatalysts for Efficient Syngas Conversion to Value-Added Chemicals with High Selectivity

Syngas conversion is a key platform for efficient utilization of various carbon-containing resources including coal, natural gas, biomass, organic wastes, and even CO₂. One of the most classic routes for syngas conversion is Fischer-Tropsch synthesis (FTS), which is already available for commercial application. However, it still remains a grand challenge to tune the product distribution from paraffins to value-added chemicals such as olefins and higher alcohols. Breaking the selectivity limitation of the Anderson-Schulz-Flory (ASF) distribution has been one of the hottest topics in syngas chemistry.Metallic Co⁰ is a well-known active phase for Co-catalyzed FTS, and the products are dominated by paraffins with a small amount of chemicals (i.e., olefins or alcohols). Specifically, a cobalt carbide (Co₂C) phase is typically viewed as an undesirable compound that could lead to deactivation with low activity and high methane selectivity. Although iron carbide (Fe_xC) can produce olefins with selectivity up to ∼60%, the fraction of methane is still rather high, and the required high reaction temperature (300-350 °C) typically causes coke deposition and fast deactivation. Recently, we discovered that Co₂C nanoprisms with preferentially exposed facets of (020) and (101) can effectively produce olefins from syngas conversion under mild reaction conditions with high selectivity. The methane fraction was limited within 5%, and the product distribution deviated greatly from ASF statistic law. The catalytic performances of Co₂C nanoprisms are completely different from that reported for the traditional FT process, exhibiting promising potential industrial application.This Account summarizes our progress in the development of Co₂C nanoprisms for Fischer-Tropsch synthesis to olefins (FTO) with remarkable efficiencies and stability. The underlying mechanism for the observed unique catalytic behaviors was extensively explored by combining DFT calculation, kinetic measurements, and various spectroscopic and microscopic investigation. We also emphasize the following issues: particle size effect of Co₂C, the promotional effect of alkali and Mn promoters, and the role of metal-support interaction (SMI) in fabricating supported Co₂C nanoprisms. Specially, we briefly review the synthetic methods for different Co₂C nanostructures. In addition, Co₂C can also be applied as a nondissociative adsorption center for higher alcohol synthesis (HAS) via syngas conversion. We also discuss the construction of a Co⁰/Co₂C interfacial catalyst for HAS and demonstrate how to tune the reaction network and strengthen CO nondissociative adsorption ability for efficient production of higher alcohols. We believe that the advances in the development of Co₂C nanocatalysts described here present a critic step to produce chemicals through the FTS process.

Recent developments in catalyst pretreatment technologies for cobalt based Fisher–Tropsch synthesis

Stringent environmental regulations and energy insecurity necessitate the development of an integrated process to produce high-quality fuels from renewable resources and to reduce dependency on fossil fuels, in this case Fischer–Tropsch synthesis (FTS). The FT activity and selectivity are significantly influenced by the pretreatment of the catalyst. This article reviews traditional and developing processes for pretreatment of cobalt catalysts with reference to their application in FTS. The activation atmosphere, drying, calcination, reduction conditions and type of support are critical factors that govern the reducibility, dispersion and crystallite size of the active phase. Compared to traditional high temperature H2 activation, both hydrogenation–carbidisation–hydrogenation and reduction–oxidation–reduction pretreatment cycles result in improved metal dispersion and exhibit much higher FTS activity. Cobalt carbide (Co2C) formed by CO treatment has the potential to provide a simpler and more effective way of producing lower olefins, and higher alcohols directly from syngas. Syngas activation or direct synthesis of the metallic cobalt catalyst has the potential to remove the expensive H2 pretreatment procedure, and consequently simplify the pretreatment process, which would make it more economical and thus more attractive to industry.

Energy Storage and CO2 Reduction Performances of Co/Co2C/C Prepared by an Anaerobic Ethanol Oxidation Reaction Using Sacrificial SnO2

Co/Co2C/C hybrids were prepared employing a new synthetic route and demonstrated as materials for energy storage and CO2 recycling application. Herein, an anaerobic ethanol oxidation reaction over Co3O4 nanoparticles (NPs) was first employed to fabricate Co/Co2C/C hybrids using sacrificial SnO2. In the absence of SnO2, Co3O4 NPs were converted to alpha and beta metallic Co. On the other hand, using sacrificial SnO2 resulted in the formation of Co2C and Co embedded in the carbon matrix at approximately 450 °C, as determined by temperature-programmed mass spectrometry analysis. The newly developed materials were fully examined by X-ray diffraction crystallography, scanning electron microscopy, energy-dispersive X-ray analysis, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. The Co/Co2C/C hybrids showed a specific capacitance of 153 F/g at a current density of 0.5 A/g. Photocatalytic CO2 reduction experiments were performed and generated CO, CH4, and CH3OH as reduction products with yields of 47.7, 11.0, and 23.4 μmol/g, respectively. The anaerobic ethanol oxidation reaction could be a very useful method for the development of carbon-supported metal carbides, which have not been achieved by other synthetic methods. Furthermore, the demonstration tests unveiled new application areas of Co carbide materials.

Theoretically predicted surface morphology of FCC cobalt nanoparticles induced by Ru promoter

The addition of Ru promoter has an important role in tuning the stability of the exposed facets of FCC Co NPs, accompanied by the change of surface morphology.

Investigation of the deactivation behavior of Co catalysts in Fischer–Tropsch synthesis using encapsulated Co nanoparticles with controlled SiO2 shell layer thickness

The deactivation behavior of Co catalysts was clearly elucidated using Co nanoparticles confined by a porous SiO₂ shell layer with varying thickness and different reaction temperatures.

Promoted cobalt metal catalysts suitable for the production of lower olefins from natural gas

Due to the surge of natural gas production, feedstocks for chemicals shift towards lighter hydrocarbons, particularly methane. The success of a Gas-to-Chemicals process via synthesis gas (CO and H2) depends on the ability of catalysts to suppress methane and carbon dioxide formation. We designed a Co/Mn/Na/S catalyst, which gives rise to negligible Water-Gas-Shift activity and a hydrocarbon product spectrum deviating from the Anderson-Schulz-Flory distribution. At 240 °C and 1 bar, it shows a C2-C4 olefins selectivity of 54%. At 10 bar, it displays 30% and 59% selectivities towards lower olefins and fuels, respectively. The spent catalyst consists of 10 nm Co nanoparticles with hcp Co metal phase. We propose a synergistic effect of Na plus S, which act as electronic promoters on the Co surface, thus improving selectivities towards lower olefins and fuels while largely reducing methane and carbon dioxide formation.

Co3 O4 /Fe0.33 Co0.66 P Interface Nanowire for Enhancing Water Oxidation Catalysis at High Current Density

Designing well-defined nanointerfaces is of prime importance to enhance the activity of nanoelectrocatalysts for different catalytic reactions. However, studies on non-noble-metal-interface electrocatalysts with extremely high activity and superior stability at high current density still remains a great challenge. Herein, a class of Co₃ O₄ /Fe_0.33 Co_0.66 P interface nanowires is rationally designed for boosting oxygen evolution reaction (OER) catalysis at high current density by partial chemical etching of Co(CO₃ )_0.5 (OH)·0.11H₂ O (Co-CHH) nanowires with Fe(CN)₆ ^3- , followed by low-temperature phosphorization treatment. The resulting Co₃ O₄ /Fe_0.33 Co_0.66 P interface nanowires exhibit very high OER catalytic performance with an overpotential of only 215 mV at a current density of 50 mA cm^-2 and a Tafel slope of 59.8 mV dec^-1 in 1.0 m KOH. In particular, Co₃ O₄ /Fe_0.33 Co_0.66 P exhibits an obvious advantage in enhancing oxygen evolution at high current density by showing an overpotential of merely 291 mV at 800 mA cm^-2 , much lower than that of RuO₂ (446 mV). Co₃ O₄ /Fe_0.33 Co_0.66 P is remarkably stable for the OER with negligible current loss under overpotentials of 200 and 240 mV for 150 h. Theoretical calculations reveal that Co₃ O₄ /Fe_0.33 Co_0.66 P is more favorable for the OER since the electrochemical catalytic oxygen evolution barrier is optimally lowered by the active Co- and O-sites from the Co₃ O₄ /Fe_0.33 Co_0.66 P interface.

Recent progress in improving the stability of copper-based catalysts for hydrogenation of carbon–oxygen bonds

Five different strategies to enhance the stability of Cu-based catalysts for hydrogenation of C–O bonds are summarized in this review.