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Co2C nanostructures play a vital role in selective production of value-added chemicals via syngas conversion. Recent advances in Co2C-based nanocatalysts for Fischer–Tropsch to olefin reactions are summarized in this feature article.

Alkaline-earth metal promoted CoMn catalysts with higher surface basicity benefit the carburization of CoMn oxides to form more Co2C nanoprisms for olefin formation, especially for long-chain olefins.

The RhK/Mo2C catalyst exhibited remarkable selectivity for higher alcohols synthesis from syngas under mild reaction conditions owing to the interface sites between Rh and Mo2C promoted by K, which greatly facilitated CO insertion.

Selective oxidation of methane to oxygenates using low-cost and environment-friendly molecular oxygen (O2) under mild reaction conditions is a promising strategy but still remains grand challenge. It is of great importance to accelerate the activation of O2 to generate highly active oxygen species, such as hydroxyl peroxide and hydroxyl species to improve catalytic performance for selective oxidation of methane. Selective oxidation of methane using O2 by coupling in-situ generation of hydrogen peroxide via tandem catalysis ensures the easy formation of active oxygen species for methane activation, leading to high oxygenates productivity under mild conditions. In this concept, we summarized the recent progresses for selective oxidation of methane to oxygenates using O2 based on tandem catalysis by coupling with in-situ generation of hydrogen peroxide. The remaining challenges and future perspectives for selective oxidation of methane to oxygenates via tandem catalysis were also proposed.

Na-promoted colloidal Ru NPs exhibit high efficiency for aqueous-phase FTS to produce oxygenates from syngas.

A multifunctional catalyst composed of CoMn and CuZnAlZr oxides can dramatically increase higher-alcohol selectivity. However, the role of Cu-based components and catalytic mechanism are still uncl...

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 (FexC) 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.

A green route for one−pot synthesis of acetals by tandem hydroformylation−acetalization of olefins using supported Rh−based catalysts was developed. Experimental results demonstrated that suitable Rh loading (1 wt%) with appropriate reaction temperature (120 °C) and reaction time (8 h) were favorable for the formation of acetals, and a high acetals selectivity of 94.6% was achieved. More importantly, the selectivity to valuable linear products was enhanced in this tandem catalysis. Based on the catalytic mechanism study, highly dispersed RhOx nanoparticles and abundant acid sites on the supports were responsible for the hydroformylation and acetalization, respectively. One-pot synthesis of acetals directly from olefins with high selectivity was achieved over heterogeneous bifunctional catalysts via tandem hydroformylation-acetalization.

Selectivity control of nitrobenzene hydrogenation remains a great challenge, and it is desirable to develop a green and highly efficient catalytic route toward value-added metastable intermediate products. Herein, we reported that isolated Ru single atoms coordinated with oxygen atoms in CeO2 (Ru-SAs/CeO2) can achieve chemoselective hydrogenation of nitrobenzene to azoxybenzene with a selectivity of 88.2% in a continuous flow reactor using H2 without using any bases or expensive organic reducing agents, while 82.7% aniline selectivity was obtained by Ru nanoparticles. We demonstrated that the unique coordinated structure between Ru single atoms and O atoms preferentially controls the reaction route toward the coupling of nitrosobenzene and phenylhydroxylamine intermediates to form azoxybenzene while greatly suppressing over-hydrogenation. The present work provides an efficient strategy to regulate the reaction pathway of nitrobenzene hydrogenation with a green and industry-friendly process by designing highly dispersed Ru single atoms.

A Ru single-atom (Ru SA) catalyst supported on activated carbon was adopted to synthesize 3-pentanone with 83.3% selectivity via heterogeneous ethylene hydroformylation, while 52.1% ethane selectivity was obtained for Ru nanoparticles (Ru NPs). The atomically dispersed Ru species with oxidation state (Ruδ+) and Ru-C4O coordination structure were identified as the active sites for efficient C–C coupling to generate 3-pentanone, while metallic Ru nanoparticles exhibited high activity for ethylene hydrogenation to ethane. Density functional theory (DFT) calculation revealed that the energy barrier of the direct coupling of C2H5CO* with C2H5* to form 3-pentanone on Ru SA was much lower than that on Ru NPs. As a result, the formation of 3-pentanone over Ru SA was more favourable than propanal, which was admittedly generated via coupling of C2H5CO* and H*. This strategy may provide a potential green route for the one-pot synthesis of 3-pentanone with high atomic economy.

Selective oxidation of methane to oxygenates with O

Cobalt carbide (Co2C) exhibits strong facet effect for Fischer-Tropsch to olefins (FTO) reaction. Herein, we report that the facet proportion of Co2C nanostructures can be tuned effectively by incorporating and altering the Mn content in the CoMn composite oxide as catalyst precursor. With the addition of Mn promoter, the Co2C nanoprisms with exposed (020) and (101) facets are generated under reaction conditions. In addition, the facet proportion of Co2C(020) facet can be effectively improved by enhancing the Mn/Co ratio. With the increase of facet proportion of Co2C(020)/Co2C(101) ratio, the as-obtained Co2C nanoprisms exhibit higher intrinsic activity and lower methane selectivity during the syngas conversion process. Kinetic experiments also demonstrate that the apparent activation energy (E-a) for CO conversion is significantly reduced as increasing the facet proportion of Co2C(020). This work provides a simple and feasible way to tune the exposed facet proportion for the rational design of Co2C nanocatalyst for FTO reaction.

Direct synthesis of aromatics from syngas was investigated by coupling Fischer–Tropsch to olefins (FTO) reaction and aromatization process. The CoMnAl composite oxides enabled the formation of olef...

Cobalt carbide (Co2C) nanoprisms derived from CoMn composite oxides exhibit promising catalytic performance for Fischer–Tropsch to olefins (FTO) synthesis via H2-lean syngas conversion, but with ne...

Selective synthesis of higher oxygenates (linear α-alcohols and α-aldehydes, C 2 + OH) from syngas is highly attractive but remains challenging owing to the low C 2 + OH selectivity and low catalytic stability. Herein we introduce a multifunctional catalyst composed of CoMn and CuZnAlZr oxides that dramatically increased the oxygenates selectivity to 58.1 wt %, where more than 92.0 wt % of the produced oxygenates are C 2 + OH. Notably, the total selectivity to value-added chemicals including oxygenates and olefins reached 80.6 wt % at CO conversion of 29.0 % with high stability. The appropriate component proximity can effectively suppress the formation of the undesired C1 products, and the selectively propulsion of reaction network by synergetic effect of different components contributes to the enhanced selectivity to higher oxygenates. This work provides an alternative strategy for the rational design of new catalysts for direct conversion of syngas into higher oxygenates with co-production of olefins.

Direct production of olefins via syngas conversion over a Co2C-based catalyst was investigated in a slurry bed reactor (SBR). It was found that the total selectivities to olefins and oxygenates reached 88.8C% at a CO conversion of 29.5% at 250 °C, 5 bar and H2/CO = 0.5. The hydrocarbon distribution greatly deviated from the classical Anderson–Schulz–Flory (ASF) distribution, with only 2.6C% methane selectivity was obtained. XRD and TEM characterization verified that the Co2C nanoprisms with special exposed facts of (101) and (020) constitutes the Fischer–Tropsch to olefins (FTO) active site. The catalytic activity increased gradually with rising the reaction temperature, while the product distribution almost kept unchanged under various reaction condition in SBR. Compared to the reaction in FBR, the Co2C-based catalyst exhibited relative better catalytic performance during FTO process in SBR. Specifically, a higher CO conversion, a lower methane selectivity and a higher total selectivities to olefins and oxygenates were achieved in SBR. In addition, the catalyst can be in situ reduced in slurry bed reactor at mild temperature (300 °C) and no obvious deactivation was found within nearly 100 h time-on-stream, which suggested a promising route for the direct production of olefins via syngas in industrial application.

Co2C-based catalysts with SiO2, γ-Al2O3, and carbon nanotubes (CNTs) as support materials were prepared and evaluated for the Fischer-Tropsch to olefin (FTO) reaction. The combination of catalytic performance and structure characterization indicates that the cobalt-support interaction has a great influence on the Co2C morphology and catalytic performance. The CNT support facilitates the formation of a CoMn composite oxide during calcination, and Co2C nanoprisms were observed in the spent catalysts, resulting in a product distribution that greatly deviates from the classical Anderson-Schulz-Flory (ASF) distribution, where only 2.4 C% methane was generated. The Co3O4 phase for SiO2- and γ-Al2O3-supported catalysts was observed in the calcined sample. After reduction, CoO, MnO, and low-valence CoMn composite oxide were generated in the γ-Al2O3-supported sample, and both Co2C nanospheres and nanoprisms were identified in the corresponding spent catalyst. However, only separated phases of CoO and MnO were found in the reduced sample supported by SiO2, and Co2C nanospheres were detected in the spent catalyst without the evidence of any Co2C nanoprisms. The Co2C nanospheres led to a relatively high methane selectivity of 5.8 C% and 12.0 C% of the γ-Al2O3- and SiO2-supported catalysts, respectively. These results suggest that a relatively weak cobalt-support interaction is necessary for the formation of the CoMn composite oxide during calcination, which benefits the formation of Co2C nanoprisms with promising catalytic performance for the sustainable production of olefins via syngas.

The size effect of the CoxMn1−xO precursor on the formation of Co2C nanoprisms and the structure–performance relationship for the Fischer–Tropsch to olefins (FTO) reaction was investigated. CoxMn1−xO precursors with different sizes from 6.5 nm to 16.7 nm were fabricated by calcination at different temperatures. The CoxMn1−xO with small size possessed high concentration of oxygen vacancies, which promoted the dissociation of CO to form active C* species, and more Co2C nanoprisms with small size could be generated. In addition, the catalytic performance also changed with the size of the precursor. The olefin formation rate significantly increased from 3.36 to 12.48 μmol gCoxMn1−xO−1 h−1 as the CoxMn1−xO size decreased from 16.7 to 6.5 nm. This work clearly elucidates the size effect of the CoxMn1−xO precursor on the structure–performance relationship and may provide a practical and simple strategy to fabricate highly efficient CoMn catalysts for the FTO reaction.

Cu single atoms embedded in the C3N4 (Cu-SAs/C3N4) matrix exhibited high activity with 95% oxygenate selectivity for the direct conversion of methane at ambient temperature. The presence of abundant anchoring sites in C3N4 led to highly dispersed Cu–N4 moieties, which were suggested to be the underlying active sites for methane conversion.

The effect of reaction pressures on structure–performance of Co2C-based catalyst for syngas conversion was studied in detail. Co2C nanoprisms with exposed facets of (101) and (020) used for the dissociation adsorption of CO molecules were stable at low reaction pressure, and promising FTO (Fischer–Tropsch to olefins) performance with low CH4 selectivity and high C2–4= selectivity simultaneously was achieved. With the increase of reaction pressure, the oxygenates selectivity significantly increased at the expense of decreasing C2–4= selectivity. The characterization results indicated that the morphology of Co2C nanostructures changed from nanoprisms to nanospheres and that the metallic Co0 was observed with the increase of reaction pressures. The appearance of Co2C(111) benefited CO insertion, and the formation of Co/Co2C(111) as dual active sites contributed to the enhancement of oxygenates selectivity at elevated pressure. This study suggested that reaction pressures had a strong effect on structure–perf...

Fischer-Tropsch to olefins (FTO) is recognized as a surface-catalyzed structure-sensitive reaction, and the catalytic performance is strongly influenced by the morphology and exposed facets of the active phase. Here we report the effect of the reduction process on the morphology of the active phase and the catalytic performance for FTO over the CoMn catalyst. For the catalysts reduced by 10% CO-300 °C, 10% H2-300 °C and 10% H2-250 °C, Co2C nanoprisms were formed after reaching the steady state. However, for the catalysts reduced by CO-300 °C and 10% H2-400 °C, Co2C nanospheres were found instead. Both Co2C nanoprisms and nanospheres were present for the spent sample reduced by 10% H2-350 °C. Kinetic study found Co2C nanospheres to possess higher activation energy, and are more sensitive to hydrogen than Co2C nanoprisms. Density functional theory (DFT) calculations were also performed to clarify the structure-performance relationship of Co2C nanostructures for syngas conversion.

The Fischer-Tropsch to olefins (FTO) process is a promising alternative non-petroleum route to produce value-added olefins. In this study, Co2C nanoprisms formed via the CoMn spinel structure were used as the active phase for the FTO reaction and the product distribution was thoroughly investigated. A break from the traditional ASF model was found with much lower methane selectivity than that predicted by the ideal ASF law. In addition, the as-obtained hydrocarbons were mainly concentrated in the range of C2 to C12 with the C2-12 selectivity as high as 91% while the C13+ selectivity as low as 5%, indicating a much narrower distribution, which was rarely observed in the FT reaction. Moreover, ∼86% of the hydrocarbon products were olefins with very high olefin to paraffin ratios, suggesting a promising route for the selective production of olefins directly from syngas. A modified ASF distribution model was proposed with three different chain growth probabilities to rationalize the non-ASF phenomenon.

Fischer-Tropsch synthesis (FTS) is a structure-sensitive reaction for sustainable production of green fuels and value-added chemicals via syngas derived from coal, biomass, shale gas and natural gas. The nanostructure of a Fischer-Tropsch (FT) catalyst plays a crucial role in its catalytic performance. This review summarizes recent advances in the investigation of nanoeffects of FT catalysts, especially the effects of the active phase, particle size and exposed facet on catalytic performance. Perspectives and challenges for further research in nanocatalysis for syngas conversion are also given.

Flowerlike ZIF-67 micro/nano composite structures were developed by the evolution of ZIF-67 rhombododecahedrons ZIF-67(r) via facile ion-assistant solvothermal treatment. The morphology evolution of ZIF-67 with time-on-stream was studied. The flowerlike Co3O4 micro/nano composite were formed under calcination at relatively low temperature. The flowerlike Co3O4 micro/nano composite structures showed good catalytic properties for photocatalytic degradation of RhB (83.2%), higher than that of Co3O4(p) (69.7%) and Co3O4(r) (75.7%) after 90 min irradiation.

CoMn model catalysts were prepared by co-precipitation and evaluated for higher alcohol synthesis (HAS) via syngas. The selectivity to oxygenates (mainly alcohols and aldehydes) was found to be higher than 20 C% for the Na-promoted CoMn catalyst. Among the oxygenates, C2+ and C6+ fractions accounted for >90 wt% and ∼50 wt%, respectively. Metallic Co0 particles and MnCO3 were found in both Na-promoted and unpromoted CoMn catalysts after the reaction, whereas Co2C nanoparticles could only be observed in the spent Na-promoted catalyst. The addition of Na benefited the carbonization of cobalt and increased the selectivity to oxygenates and CO2. Our studies thus suggested that Co/Co2C were the bifunctional dual-sites for the oxygenates formation over the Na-promoted CoMn catalyst, where Co catalyzed CO dissociation and chain propagation, while Co2C was responsible for CO non-dissociative activation and subsequent insertion. In addition, the sole Co2C nanoparticles with certain exposed facets may also act as another kind of active dual-sites for oxygenates formation.

Co2C nanoprisms exhibit promising catalytic performance for Fischer-Tropsch synthesis to olefins (FTO) but with high CO2 selectivity (>40%). Herein, silica-coated CoMn-based catalyst was designed to limit CO2 production and remained Co2C nanoprisms as active sites unchanged. With a desired coating amount of silica, CO2 selectivity was significantly suppressed to 15.1 C% while enhancing olefins selectivity from 39.7 C% to 58.8 C%, which also shows at least 160 h of stability. It is suggested the silica-coating not only reduces the adsorption capacity of H2O, but also promotes the fast transfer of H2O away from active sites due to the higher adsorption energy of H2O on SiO2 surface, thus suppressing water-gas-shift-reaction (WGSR) activity. Moreover, the sodium promoter can counteract the H2-enrichment effect caused by SiO2-coating and largely restrain CH4 formation and olefins hydrogenation. This work provides an effective strategy to suppress CO2 formation and enhance the carbon efficiency of FTO process.

SiO2 supported Co2C-based catalysts were used for Fischer-Tropsch to olefins (FTO), and the effect of thermal pretreatment of SiO2 support under different temperatures on the Co2C morphology and catalytic performance was investigated. It was found that the interaction between cobalt and support was weakened when SiO2 was pretreated at high temperature (990 °C) due to the decreased content of surface Si OH groups. The relative weak interaction between cobalt and support benefited the formation of cobalt manganese composite oxide after calcination and reduction, and thus promoted the generation of Co2C nanoprisms with promising FTO performance. In contrast, for the SiO2 support pretreated at 350 °C or 650 °C, the strong interaction between cobalt and support led to phase separation of cobalt and manganese. As a result, only Co2C nanospheres were generated which displayed low activity and high methane selectivity.

Tandem hydroaminomethylation is an efficient and green route for one-pot synthesis of amines directly from olefins. Herein, heterogeneous hydroxyapatite (HAP) supported single-atom Rh catalyst was prepared and used for tandem hydroaminomethylation of olefins. Characterization techniques confirmed the atomic dispersion of Rh species on HAP. Up to 99% conversion of 1-hexene with high selectivity to the desired amines (93.2%) was obtained over 0.5Rh1/HAP catalyst. Mechanism study demonstrated that the first hydroformylation step during the tandem catalytic process was rate-determining. Compared with the Rh nanoparticles on other oxide supports (Mg3Al, MgO and Al2O3), the atomically dispersed Rh sites on HAP ensured the high hydroformylation activity, thereby guaranteed the outstanding catalytic performance for the total tandem process. Furthermore, various corresponding amines can be obtained with satisfactory yields over 0.5Rh1/HAP catalyst from a wide scope of olefins or amines substrates.

The Fischer–Tropsch to olefins (FTO) reaction over Co2C catalysts is structure-sensitive, as the catalytic performance is strongly influenced by the surface structure of the active phase. The exposed facets determine the surface structure, and it remains a great challenge to precisely control the particle morphology of the FTO active phase. In this study, the controlling effect of the Mn promoter on the final morphology of the Co2C nanoparticles for the FTO reaction was investigated. The unpromoted catalyst and several promoted catalysts with Ce, La, and Al were also studied for comparison. For the Mn-promoted catalysts, the combination method of the Co and Mn components plays a crucial role in the final morphology of Co2C and thus the catalytic performance. For the CoMn catalyst prepared by coprecipitation, Co2C nanoprisms with specifically exposed facets of (101) and (020) can be obtained, which exhibit a promising FTO catalytic performance with high C2–4= selectivity, low methane selectivity, and high ...

A series of Co/SiO2 catalysts with different sodium (Na) loadings (0, 0.1, 0.2, 0.5 and 1 wt%) were prepared and evaluated for Fischer-Tropsch reaction to study the effect of Na on the catalyst structure and catalytic performance. The addition of Na was found to decrease the catalytic activity and hydrocarbon selectivity, but increase CO2 selectivity due to the enhanced WGS activity. The addition of Na also resulted in higher selectivity to oxygenates (alcohols and aldehydes) and O/P ratio as well as the shift of hydrocarbons to lower carbon numbers. Structure characterization revealed a decrease in the surface area and particles size for the calcined samples with the addition of Na. Co2C was formed during the reaction process for the Na-promoted catalysts. As a result, a new Co/Co2C bifunctional active sites were generated for oxygenates formation leading to increasing oxygenates selectivity. In addition, the Co2C nanoparticles alone may also act as dual active sites for oxygenate formation at high reaction pressure over the promoted catalysts with high Na loading.

Syngas conversion to fuels and chemicals is one of the most challenging subjects in the field of C1 chemistry. It is considered as an attractive alternative non-petroleum-based production route. The direct synthesis of olefins and alcohols as high value-added chemicals from syngas has drawn particular attention due to its process simplicity, low energy consumption and clean utilization of carbon resource, which conforms to the principles of green carbon science. This review describes the recent advances for the direct production of lower olefins and higher alcohols via syngas conversion. Recent progress in the development of new catalyst systems for enhanced catalytic performance is highlighted. We also give recommendations regarding major challenges for further research in syngas conversion to various chemicals.

The effects of a sodium (Na) promoter on the catalytic performance of cobalt-manganese (CoMn) catalysts for Fischer–Tropsch to olefin (FTO) reactions were investigated. For the sample without Na, Co0 was found to be the active phase for the traditional Co-based Fischer–Tropsch reaction with low CO2 selectivity. The olefin/paraffin (O/P) ratio was found to be low with a C2–4= selectivity of only 15.4 C%. However, with the addition of Na, cobalt carbide (Co2C) quadrangular nanoprisms with the (101) and (020) facets exposed were formed. The Co2C nanoprisms displayed a high C2–4= selectivity (54.2 C%) as well as a low methane selectivity (5.9 C%) under mild reaction conditions. The O/P ratio for C2–4 reached 23.9, and the product distribution deviated greatly from the classical Anderson–Schulz–Flory (ASF) distribution. Co2C nanoprisms were considered to be an effective FTO active phase with strong facet effects. The Na promoter played a key role in the evolution of the FTO catalysts. The addition of Na, which...

Higher alcohols synthesis (HAS) from syngas with high selectivity attracts great attention but remains challenging. Herein, we reported an effective strategy by tuning chemical environment and synergistic relay reaction to promote the production of higher alcohols. CO insertion rate was greatly enhanced by introducing Rh or Ru component to CoMn oxides. The catalytic activity and oxygenates selectivity increased dramatically over the as-obtained Rh-CoMn or Ru-CoMn catalyst, while the fraction of C2+OH in oxygenates maintained >92 %. Multiple studies demonstrated the highly dispersed Rhδ+ or Ruδ+ species not only effectively tuned the chemical environment and facilitated the stable existence of Co2C, but also catalyzed the coupling of syngas and in-situ generated olefins to produce extra oxygenates via hydroformylation route. The synergistic effect of Co0, Co2C and Rhδ+ (or Ruδ+) species, as well as the promotional effect of olefins relay reaction contributed to the enhancement in both higher alcohols selectivity and CO conversion.

Lower olefins-generally referring to ethylene, propylene and butylene-are basic carbon-based building blocks that are widely used in the chemical industry, and are traditionally produced through thermal or catalytic cracking of a range of hydrocarbon feedstocks, such as naphtha, gas oil, condensates and light alkanes. With the rapid depletion of the limited petroleum reserves that serve as the source of these hydrocarbons, there is an urgent need for processes that can produce lower olefins from alternative feedstocks. The 'Fischer-Tropsch to olefins' (FTO) process has long offered a way of producing lower olefins directly from syngas-a mixture of hydrogen and carbon monoxide that is readily derived from coal, biomass and natural gas. But the hydrocarbons obtained with the FTO process typically follow the so-called Anderson-Schulz-Flory distribution, which is characterized by a maximum C2-C4 hydrocarbon fraction of about 56.7 per cent and an undesired methane fraction of about 29.2 per cent (refs 1, 10, 11, 12). Here we show that, under mild reaction conditions, cobalt carbide quadrangular nanoprisms catalyse the FTO conversion of syngas with high selectivity for the production of lower olefins (constituting around 60.8 per cent of the carbon products), while generating little methane (about 5.0 per cent), with the ratio of desired unsaturated hydrocarbons to less valuable saturated hydrocarbons amongst the C2-C4 products being as high as 30. Detailed catalyst characterization during the initial reaction stage and theoretical calculations indicate that preferentially exposed {101} and {020} facets play a pivotal role during syngas conversion, in that they favour olefin production and inhibit methane formation, and thereby render cobalt carbide nanoprisms a promising new catalyst system for directly converting syngas into lower olefins.

Dual active sites play a vital role in higher alcohols synthesis (HAS) from syngas and the relative proportion of each active sites may greatly affect the contact boundaries between the dual active sites and the reaction network. Herein, we regulated the ratio of Co0/Co2C dual active sites by changing the content of Na promoter, and investigated the structure-performance relationship of Co0/Co2C for HAS. It was found that both of the catalytic activity and paraffins selectivity increased with the increase of Co0/Co2C ratio, while the formation of olefins was inhibited. However, the oxygenates selectivity exhibited a volcano variation trend. The results suggested that only when the Co0/Co2C ratio was in the appropriate range, the strong synergistic effect of Co0/Co2C dual-site could be obtained, and the CO insertion rate can thus match well with hydrogenation rate and chain-growth rate, which benefited for the oxygenates formation.

The effects of preparation methods for CoMn-based catalysts on the precursor phase of Co species, the morphology of Co2C nanostructures as well as the catalytic performance for Fischer-Tropsch to olefins were investigated. Five catalysts prepared by precipitation and impregnation methods were compared in detail. CoMn spinel oxide was found in the calcined catalysts prepared by co-precipitation or sequential precipitation starting from the Co salt. However, Co3O4 and MnO2 were the major phases for the calcined catalysts prepared by sequential precipitation starting from the Mn salt or impregnation methods. During the syngas conversion process, Co2C nanoprisms with exposed facets of (101) and (020) were generated from CoMn spinel phase, and exhibited high CO conversion, low methane selectivity and high olefins selectivity. In contrast, Co2C nanospheres carburized from metallic Co or CoO were observed for the other samples with poorer FTO catalytic performance.