Effect of the support on cobalt carbide catalysts for sustainable production of olefins from syngas

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‐andγ‐Al2O3‐supported catalysts was observed in the calcined sample.After reduction,CoO,MnO,and low‐valence CoMn composite oxide were generated in theγ‐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 theγ‐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.

High coercivity cobalt carbide nanoparticles as electrocatalysts for hydrogen evolution reaction

Cobalt carbide nanoparticles(NPs),as a typical carbide material,have attracted extensive attention in the fields of magnetism and electrochemistry.Herein,we adopted a modified solution route by pyrolysis long-chain amines at high temperatures to obtain Co_(2)C NPs,in which different forms of Co NPs were used as precursors.The results reveal that no matter what the structure of the precursor and the type of long-chain amine,single-phase Co_(2)C NPs with good crystallinity are obtained.At the same time,carbonization of hexagonal close packed(hcp)cobalt as the precursor gives the materials high magnetic anisotropy,exhibiting a large coercivity(~1,300 Oe)on the nanoscale.In terms of catalytic properties,benefiting from intrinsically high activity of Co_(2)C NPs,the material demonstrates superior hydrogen evolution reaction(HER)performance,with optimal overpotential as low as 73 mV at the current density of 10 mA·cm^(-2).This provides new ideas for the further development of transition metal carbides(TMCs)and the improvement of their magnetic and electrocatalytic properties.

Synthesis of Commercial-Scale Tungsten Carbide-Cobalt (WC/Co) Nanocomposite Using Aqueous Solutions of Tungsten (W), Cobalt (Co), and Carbon (C) Precursors

This paper reports the chemical synthesis of tungsten carbide/cobalt (WC/Co) nanocomposite powders via a unique chemical processing technique, involving the using of all water soluble solution of W-, Co- and C-precursors. In the actual synthesis, large quantities of commercial-scale WC-Co nanocomposite powders are made by an unique combination of converting a molecularly mixed W-, Co-, and C-containing solutions into a complex inorganic polymeric powder precursor, conversion of the inorganic polymeric precursor powder into a W-Co-C-O containing powder intermediates using a belt furnace with temperature at about 500°C - 600°C in an inert atmosphere, followed by carburization in a rotary furnace at temperature less than 1000°C in nitrogen. Liquid phase sintering technique is used to consolidate the WC/Co nanocomposite powder into sintered bulk parts. The sintered parts have excellent hardness in excess of 93 HRA, with WC grains in the order of 200 - 300 nm, while Co phase is uniformly distributed on the grain boundaries of the WC nanoparticles. We also report the presence of cobalt Co precipitates inside tungsten carbide WC nanograins in the composites of the consolidated bulk parts. EDS is used to identify the presence of these precipitates and micro-micro-diffraction technique is employed to determine the nature of these precipitates.

Recovery of Tungsten and Cobalt from Wasted Tungsten Carbide

The collected tungsten carbide/cobalt scrapped waste typically contains approximately 90% tungsten carbide and 10% cobalt.A nitric method is used to extract tungsten and cobalt from tungsten-containing waste.The waste is first dissolved in nitric acid,which then makes cobalt soluble and becomes cobalt nitrate solution.The waste also oxidizes tungsten carbide to insoluble tungstenic acid precipitate.If tungsten carbide scraps are obtained from leftover of LCD glass cutting,after applying the same process as above,the remaining glass also needs to be separated from the tungstenic acid.XRF analysis shows that 93.8% of cobalt and 97.72% of tungsten can be obtained separately by this wet chemical method.By ICP analysis,no more tungsten ion remains after 2 h reaction in the cobalt recovery when 12 N of nitric acid is used for oxidation.The recovery materials obtained for tungsten are tungsten oxide and for cobalt a mixture of Co3O4 and CoO.

Bidirectionally catalytic polysulfide conversion by high-conductive metal carbides for lithium-sulfur batteries

Utilizing catalysts to accelerate the redox kinetics of lithium polysulfides (LiPSs) is a promising strategy to alleviate the shuttle effect of lithium–sulfur (Li–S) batteries.Nevertheless,most of the reported catalysts are only effective for LiPSs reduction,resulting in the devitalization of catalysts over extended cycles as a consequence of the continuous accumulation of Li_(2)S passivation layer.The situation gets even worse when employing mono-directional catalyst with poor electron conductivity because the charge transfer for the decomposition of solid Li_(2)S is severely hampered.Herein,a high-conductive and dualdirectional catalyst Co_(3)C decorated on porous nitrogen-doped graphene-like structure and carbon nanotube (Co_(3)C@PNGr-CNT) is fabricated as sulfur host,which not only promotes the precipitation of Li_(2)S from Li PSs during discharge but also facilitates the decomposition of Li;S during subsequent charge,as evidenced by the reduced activation energies for both reduction and oxidation processes.Furthermore,the long-term catalytic stability of Co_(3)C is corroborated by the reversible evolution of Co–C bond length over extended cycles as observed from X-ray absorption fine structure results.As a consequence,the fabricated Co_(3)C@PNGr-CNT/S cathode delivers a low capacity decay of 0.043%per cycle over 1000 cycles at 2C.Even at high sulfur loading (15.6 mg cm^(-2)) and low electrolyte/sulfur (E/S) ratio (~8μL mg^(-1))conditions,the battery still delivers an outstanding areal capacity of 11.05 m Ah cm^(-2) after 40 cycles.This work provides a rational strategy for designing high-efficient bidirectional catalyst with single component for high-performance Li-S batteries.

Effect of Sodium on the Structure-Performance Relationship of Co/SiO2 for Fischer-Tropsch Synthesis

A series of Co/SiO2 catalysts with different sodium （Na）loadings （0, 0.1, 0.2, 0.5 and I 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 selec- tivity due to the enhanced WGS activity. The addition of Na also resulted in higher selectivity to oxygenates （alco- hols and aldehydes） and O/P ratio as well as the shift of hydrocarbons to lower carbon numbers. Structure charac- terization revealed a decrease in the surface area and particles size for the calcined samples with the addition of Na. CozC was formed during the reaction process for the Na-promoted catalysts. As a result, a new Co/Co2C bifunc- tional 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.