Fe-based catalysts are efficient systems for CO_(2)conversion via reverse water-gas shift(rWGS)reaction.Nevertheless,the nature of the active phase,namely metallic iron,iron oxide or iron carbide remains a subject of ...Fe-based catalysts are efficient systems for CO_(2)conversion via reverse water-gas shift(rWGS)reaction.Nevertheless,the nature of the active phase,namely metallic iron,iron oxide or iron carbide remains a subject of debate which our paper is meant to close.Fe0 is a much better catalyst for the rWGS than Fe_(3)C.The activity of Fe0 can be promoted by the addition of Cs and Cu whose presence hinders iron carburisation while favouring both higher conversion and enhanced selectivity.When the samples are aged in the rWGS reaction mixture during stability test a new phase appear:Fe_(5)C_(2),resulting in a more active but less selective catalysts than Fe0 for the rWGS reaction.Hence our results indicate that we could potentially achieve an optimal activity/selective balance upon finely tuning the proportion Fe/Fe_(5)C_(2).Beyond the fundamental information concerning active phase we have observed the presence of advanced Fischer-Tropsch-like products at ambient pressure opening new opportunities for the design of hybrid rWGS/Fischer-Tropsch systems.展开更多
CO2 methanation with Hydrogen to form CH4 offers a solution for off-peak renewable energy storage. γ-alumina-supported Mo and Ni-Mo catalysts were used in CO2 methanation, either in their reduced or in their carburiz...CO2 methanation with Hydrogen to form CH4 offers a solution for off-peak renewable energy storage. γ-alumina-supported Mo and Ni-Mo catalysts were used in CO2 methanation, either in their reduced or in their carburized form. The presence of Ni improved the carburization extent of Mo-species, resulting in increased catalytic activity and selectivity for the catalytic CO2 methanation reaction. Carburization generally enhances the basicity of the materials and thus CO2 absorption on their surface. At 300°C, the conversions of CO2 for the reduced Ni-Mo/Al2O3 catalyst and Ni-Mo2C/Al2O3 catalysts were 5.3% and 13.8% respectively with a corresponding selectivity in CH4 of 10.0% and 98.1%, respectively.展开更多
Nanocrystalline tungsten carbide thin films were fabricated on graphite substrates by plasma enhanced chemical vapor deposition （PECVD） at H2 and Ar atmosphere, using WF6 and CH4 as precursors. The crystal phase, st...Nanocrystalline tungsten carbide thin films were fabricated on graphite substrates by plasma enhanced chemical vapor deposition （PECVD） at H2 and Ar atmosphere, using WF6 and CH4 as precursors. The crystal phase, structure and chemical components of the films were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and energy-dispersive spectrometer （EDS）, respectively. The results show that the film prepared at CH4/WF6 concentration ratio of 20 and at 800℃ is composed of spherical particles with a diameter of 20-35 nm. Electrochemical investigations show that the electrochemical real surface area of electrode of the film is large, and the electrode of the film exhibits higher electro-catalytic activity in the reaction of methanol oxidation. The designated constant current of the film catalyst is 123.6 mA/cm^2 in the mixture solution of H2SO4 and CH3OH at the concentration of 0.5 and 2.0 mol/L at 70℃, and the designated constant potential is only 0.306 V （vs SCE）.展开更多
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 catal...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.展开更多
In the present work, the crystallographic properties of unsupported Ni-Mo catalyst serie were carried out. They were synthesized with a ratio of Mo from 10, 25, 50 to 75 wt%. The final catalysts were characterized by ...In the present work, the crystallographic properties of unsupported Ni-Mo catalyst serie were carried out. They were synthesized with a ratio of Mo from 10, 25, 50 to 75 wt%. The final catalysts were characterized by X-ray diffraction (XRD) in order to identify crystallographic phases present in the solids using DRXwinsoftware version 2.3. The crystal size was determinated by Bragg’s law. Ni-Mo catalyst model (MoC-75) structure was modeled by Carine Crystallography Software version 3.1 which was built based on its space group and atomic positions which were previous the results of XRD. Characteristical phases of Ni-Mo Carbides were identified for their typical planes (111), (200) and (311) for Ni-Mo series and the plane (101) for the a Mo-C series.展开更多
Reverse water gas shift（RWGS） reaction can be served as a pivotal stage of transitioning the abundant CO;resource into chemicals or hydrocarbon fuels, which is attractive for the CO;utilization and of eventually sig...Reverse water gas shift（RWGS） reaction can be served as a pivotal stage of transitioning the abundant CO;resource into chemicals or hydrocarbon fuels, which is attractive for the CO;utilization and of eventually significance in enabling a rebuilt ecological system for unconventional fuels. This concept is appealing when the process is considered as a solution for the storage of renewable energy, which may also find a variety of potential end uses for the outer space exploration. However, a big challenge to this issue is the rational design of high temperature endurable RWGS catalysts with desirable CO product selectivity. In this work, we present a comprehensive overview of recent publications on this research topic,mainly focusing on the catalytic performance of RWGS reaction over three major kinds of heterogeneous catalysts, including supported metal catalysts, mixed oxide catalysts and transition metal carbides. The reaction thermodynamic analysis, kinetics and mechanisms are also described in detail. The present review attempts to provide a general guideline about the construction of well-performed heterogeneous catalysts for the RWGS reaction, as well as discussing the challenges and further prospects of this process.展开更多
The purpose of this study was to prepare iron-based catalysts supported on silica by autocombustion method for directly using for Fischer-Tropsch synthesis（FTS） without a reduction step. The effect of different citr...The purpose of this study was to prepare iron-based catalysts supported on silica by autocombustion method for directly using for Fischer-Tropsch synthesis（FTS） without a reduction step. The effect of different citric acid（CA）：iron nitrate（N） molar ratios and acid types on the FTS performance of catalysts were investigated. The CA：N molar ratios had an important influence on the formation of iron active phases and FTS activity. The iron carbide（FexC）, which is known to be one of the iron active phases, was demonstrated by the X-ray diffraction and X-ray photoelectron spectroscopy. Increasing the CA：N molar ratios up to 0.1 increased CO conversion of catalyst to 86.5%, which was then decreased markedly at higher CA：N molar ratios. An excess of CA resulted in carbon residues covering the catalyst surface and declined FTS activity. The optimal catalyst（CA：N molar ratio = 0.1） achieved the highest CO conversion when compared with other autocombustion catalysts as well as reference catalyst prepared by impregnation method, followed by a reduction step. The autocombustion method had the advantage to synthesize more efficient catalysts without a reduction step. More interestingly, iron-based FTS catalysts need induction duration at the initial stage of FTS reaction even after reduction, because metallic iron species need time to be transformed to FexC. But here, even if without reduction, FexC was formed directly by autocombustion and induction period was eliminated during FTS reaction.展开更多
Silicon carbide （SIC） has been considered a promising metal-free photocatalyst due to its unique photoelectrical properties and thermal/chemical stability. However, its performance suffers from the fast recombinatio...Silicon carbide （SIC） has been considered a promising metal-free photocatalyst due to its unique photoelectrical properties and thermal/chemical stability. However, its performance suffers from the fast recombination of charge carriers. Herein, we report mesoporous SiC nanofibers with in situ embedded graphitic carbon （SiC NFs-Cx） synthesized via a one-step carbothermal reduction between electrospun carbon nanofibers and Si powders. In the absence of a noble metal co-catalyst, the hydrogen evolution efficiency of SiC NFs-Cx is significantly improved under both simulated solar light （180.2 μmol.g-1.h-1） and visible light irradiation （31.0 ~amol-g-l-h-~） in high-pH solution. The efficient simultaneous separation of charge carriers plays a critical role in the high photocatalytic activity. The embedded carbon can swiftly transfer the photogenerated electrons and improve light absorption, whereas the additional hydroxyl anions （OH-） in high- pH solution can accelerate the trapping of holes. Our results demonstrate that the production of SiC NFs-Cx, which contains exclusively earth-abundant elements, scaled up, and is environmentally friendly, has great potential for practical applications. This work may provide a new pathway for designing stable, low- cost, high efficiency, and co-catalyst-free photocatalysts.展开更多
基金provided by the Royal Society Research Grant RSGR1180353partially sponsored by the CO2Chem UK through the Engineering and Physical Sciences Research Council(EPSRC)grant EP/P026435/1the Spanish Ministry of Science and Innovation through the projects RYC2018-024387-I and PID2019-108502RJ-I00.
文摘Fe-based catalysts are efficient systems for CO_(2)conversion via reverse water-gas shift(rWGS)reaction.Nevertheless,the nature of the active phase,namely metallic iron,iron oxide or iron carbide remains a subject of debate which our paper is meant to close.Fe0 is a much better catalyst for the rWGS than Fe_(3)C.The activity of Fe0 can be promoted by the addition of Cs and Cu whose presence hinders iron carburisation while favouring both higher conversion and enhanced selectivity.When the samples are aged in the rWGS reaction mixture during stability test a new phase appear:Fe_(5)C_(2),resulting in a more active but less selective catalysts than Fe0 for the rWGS reaction.Hence our results indicate that we could potentially achieve an optimal activity/selective balance upon finely tuning the proportion Fe/Fe_(5)C_(2).Beyond the fundamental information concerning active phase we have observed the presence of advanced Fischer-Tropsch-like products at ambient pressure opening new opportunities for the design of hybrid rWGS/Fischer-Tropsch systems.
文摘CO2 methanation with Hydrogen to form CH4 offers a solution for off-peak renewable energy storage. γ-alumina-supported Mo and Ni-Mo catalysts were used in CO2 methanation, either in their reduced or in their carburized form. The presence of Ni improved the carburization extent of Mo-species, resulting in increased catalytic activity and selectivity for the catalytic CO2 methanation reaction. Carburization generally enhances the basicity of the materials and thus CO2 absorption on their surface. At 300°C, the conversions of CO2 for the reduced Ni-Mo/Al2O3 catalyst and Ni-Mo2C/Al2O3 catalysts were 5.3% and 13.8% respectively with a corresponding selectivity in CH4 of 10.0% and 98.1%, respectively.
基金This work was supported by the National Natural Scmnce Foundation of China(Grant Nos.20276069,20476097)
文摘Nanocrystalline tungsten carbide thin films were fabricated on graphite substrates by plasma enhanced chemical vapor deposition （PECVD） at H2 and Ar atmosphere, using WF6 and CH4 as precursors. The crystal phase, structure and chemical components of the films were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and energy-dispersive spectrometer （EDS）, respectively. The results show that the film prepared at CH4/WF6 concentration ratio of 20 and at 800℃ is composed of spherical particles with a diameter of 20-35 nm. Electrochemical investigations show that the electrochemical real surface area of electrode of the film is large, and the electrode of the film exhibits higher electro-catalytic activity in the reaction of methanol oxidation. The designated constant current of the film catalyst is 123.6 mA/cm^2 in the mixture solution of H2SO4 and CH3OH at the concentration of 0.5 and 2.0 mol/L at 70℃, and the designated constant potential is only 0.306 V （vs SCE）.
基金supported by Collaborative Innovation Center of Suzhou Nano Science&Technology,the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD)the 111 Project,Joint International Research Laboratory of CarbonBased Functional Materials and Devices,the National Natural Science Foundation of China(11905154)+1 种基金the Natural Science Foundation of the Jiangsu Higher Education Institutions of China(19KJA550004)the Natural Science Foundation of Jiangsu Province(BK20190814)。
文摘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.
文摘In the present work, the crystallographic properties of unsupported Ni-Mo catalyst serie were carried out. They were synthesized with a ratio of Mo from 10, 25, 50 to 75 wt%. The final catalysts were characterized by X-ray diffraction (XRD) in order to identify crystallographic phases present in the solids using DRXwinsoftware version 2.3. The crystal size was determinated by Bragg’s law. Ni-Mo catalyst model (MoC-75) structure was modeled by Carine Crystallography Software version 3.1 which was built based on its space group and atomic positions which were previous the results of XRD. Characteristical phases of Ni-Mo Carbides were identified for their typical planes (111), (200) and (311) for Ni-Mo series and the plane (101) for the a Mo-C series.
基金supported by the Natural Science Foundation of China (21306046)the Open Project of State Key Laboratory of Chemical Engineering (SKL-Che-15C03)+2 种基金the Fundamental Research Funds for the Central Universities (WA1514013)the 111 Project of Ministry of Education of China (B08021)supported by the China Scholarship Council (CSC) for the research at Norwegian University of Science and Technology (NTNU)
基金supported by the National Natural Science Foundation of China(Nos.21506204 and 21476226)China Ministry of Science and Technology under contact of 2016YFB0600902+3 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences(XDB17020400)State Grid Cooperation of China(SGRI-DL-71-16-015)Dalian Science Foundation for Distinguished Young Scholars(2016RJ04)the Youth Innovation Promotion Association of CAS
文摘Reverse water gas shift（RWGS） reaction can be served as a pivotal stage of transitioning the abundant CO;resource into chemicals or hydrocarbon fuels, which is attractive for the CO;utilization and of eventually significance in enabling a rebuilt ecological system for unconventional fuels. This concept is appealing when the process is considered as a solution for the storage of renewable energy, which may also find a variety of potential end uses for the outer space exploration. However, a big challenge to this issue is the rational design of high temperature endurable RWGS catalysts with desirable CO product selectivity. In this work, we present a comprehensive overview of recent publications on this research topic,mainly focusing on the catalytic performance of RWGS reaction over three major kinds of heterogeneous catalysts, including supported metal catalysts, mixed oxide catalysts and transition metal carbides. The reaction thermodynamic analysis, kinetics and mechanisms are also described in detail. The present review attempts to provide a general guideline about the construction of well-performed heterogeneous catalysts for the RWGS reaction, as well as discussing the challenges and further prospects of this process.
基金financial support to the Overseas Academic Presentation Scholarship for Graduate Students, Graduate School, Chulalongkorn University
文摘The purpose of this study was to prepare iron-based catalysts supported on silica by autocombustion method for directly using for Fischer-Tropsch synthesis（FTS） without a reduction step. The effect of different citric acid（CA）：iron nitrate（N） molar ratios and acid types on the FTS performance of catalysts were investigated. The CA：N molar ratios had an important influence on the formation of iron active phases and FTS activity. The iron carbide（FexC）, which is known to be one of the iron active phases, was demonstrated by the X-ray diffraction and X-ray photoelectron spectroscopy. Increasing the CA：N molar ratios up to 0.1 increased CO conversion of catalyst to 86.5%, which was then decreased markedly at higher CA：N molar ratios. An excess of CA resulted in carbon residues covering the catalyst surface and declined FTS activity. The optimal catalyst（CA：N molar ratio = 0.1） achieved the highest CO conversion when compared with other autocombustion catalysts as well as reference catalyst prepared by impregnation method, followed by a reduction step. The autocombustion method had the advantage to synthesize more efficient catalysts without a reduction step. More interestingly, iron-based FTS catalysts need induction duration at the initial stage of FTS reaction even after reduction, because metallic iron species need time to be transformed to FexC. But here, even if without reduction, FexC was formed directly by autocombustion and induction period was eliminated during FTS reaction.
基金The work was financially supported by National Natural Science Foundation of China （Nos. 51173202 and 51203182）, Hunan Provincial Natural Science Foundation of China （No. 13JJ4009）, State Key Laboratory of Advanced Technology for Materials Synthesis and Processing （Wuhan University of Technology） （No. 2014-KF-10）, the State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology （No. G201501） and Research Project of National University of Defense Technology （No. JC13-01-05）. This work was also supported by Aid program for Science and Technology Innovative Research Team in Higher Educational Institutions of Hunan Province and Aid Program for Innovative Group of National University of Defense Technology.
文摘Silicon carbide （SIC） has been considered a promising metal-free photocatalyst due to its unique photoelectrical properties and thermal/chemical stability. However, its performance suffers from the fast recombination of charge carriers. Herein, we report mesoporous SiC nanofibers with in situ embedded graphitic carbon （SiC NFs-Cx） synthesized via a one-step carbothermal reduction between electrospun carbon nanofibers and Si powders. In the absence of a noble metal co-catalyst, the hydrogen evolution efficiency of SiC NFs-Cx is significantly improved under both simulated solar light （180.2 μmol.g-1.h-1） and visible light irradiation （31.0 ~amol-g-l-h-~） in high-pH solution. The efficient simultaneous separation of charge carriers plays a critical role in the high photocatalytic activity. The embedded carbon can swiftly transfer the photogenerated electrons and improve light absorption, whereas the additional hydroxyl anions （OH-） in high- pH solution can accelerate the trapping of holes. Our results demonstrate that the production of SiC NFs-Cx, which contains exclusively earth-abundant elements, scaled up, and is environmentally friendly, has great potential for practical applications. This work may provide a new pathway for designing stable, low- cost, high efficiency, and co-catalyst-free photocatalysts.
