The catalytic conversion of CO2 to CO via a reverse water gas shift(RWGS)reaction followed by well-established synthesis gas conversion technologies may provide a potential approach to convert CO2 to valuable chemical...The catalytic conversion of CO2 to CO via a reverse water gas shift(RWGS)reaction followed by well-established synthesis gas conversion technologies may provide a potential approach to convert CO2 to valuable chemicals and fuels.However,this reaction is mildly endothermic and competed by a strongly exothermic CO2 methanation reaction at low temperatures.Therefore,the improvement in the low-temperature activities and selectivity of the RWGS reaction is a key challenge for catalyst designs.We reviewed recent advances in the design strategies of supported metal catalysts for enhancing the activity of CO2 conversion and its selectivity to CO.These strategies include varying support,tuning metal–support interactions,adding reducible transition metal oxide promoters,forming bimetallic alloys,adding alkali metals,and enveloping metal particles.These advances suggest that enhancing CO2 adsorption and facilitating CO desorption are key factors to enhance CO2 conversion and CO selectivity.This short review may provide insights into future RWGS catalyst designs and optimization.展开更多
Propane oxidative dehydrogenation(ODH)is an energy-efficient approach to produce propylene.However,ODH suff ers from low propylene selectivity due to a relatively higher activation barrier for propylene formation comp...Propane oxidative dehydrogenation(ODH)is an energy-efficient approach to produce propylene.However,ODH suff ers from low propylene selectivity due to a relatively higher activation barrier for propylene formation compared with that for further oxidation.In this work,calculations based on density functional theory were performed to map out the reaction pathways of propane ODH on the surfaces(001)and(010)of nickel oxide hydroxide(NiOOH).Results show that propane is physisorbed on both surfaces and produces propylene through a two-step radical dehydrogenation process.The relatively low activation barriers of propane dehydrogenation on the NiOOH surfaces make the NiOOH-based catalysts promising for propane ODH.By contrast,the weak interaction between the allylic radical and the surface leads to a high activation barrier for further propylene oxidation.These results suggest that the catalysts based on NiOOH can be active and selective for the ODH of propane toward propylene.展开更多
Although possible non-homogeneous strain effects in semiconductors have been investigated for over a half century and the strain-gradient can be over 1% per micrometer in flexible nanostructures, we still lack an unde...Although possible non-homogeneous strain effects in semiconductors have been investigated for over a half century and the strain-gradient can be over 1% per micrometer in flexible nanostructures, we still lack an understanding of their influence on energy bands. Here we conduct a systematic cathodoluminescence spectroscopy study of the strain-gradient induced exciton energy shift in elastically curved CdS nanowires at low temperature, and find that the red-shift of the exciton energy in the curved nanowires is proportional to the strain-gradient, an index of lattice distortion. Density functional calculations show the same trend of band gap reduction in curved nanostructures and reveal the underlying mechanism. The significant linear straingradient effect on the band gap of semiconductors should shed new light on ways to tune optical-electronic properties in nanoelectronics.展开更多
Novel,hierarchical,flower-like Ag/Cu2O and Au/Cu2O nanostructures were successfully fabricated and applied as efficient electrocatalysts for the electrochemical reduction of CO2.Cu2O nanospheres with a uniform size of...Novel,hierarchical,flower-like Ag/Cu2O and Au/Cu2O nanostructures were successfully fabricated and applied as efficient electrocatalysts for the electrochemical reduction of CO2.Cu2O nanospheres with a uniform size of^180 nm were initially synthesized.Thereafter,Cu2O was used as a sacrificial template to prepare a series of Ag/Cu2O composites through galvanic replacement.By varying the Ag/Cu atomic ratio,Ago.12/Cu2O,having a hierarchical,flower-like nanostructure with intersecting Ag nanoflakes encompassing an inner Cu2O sphere,was prepared.The as-prepared Ag/Cu2O samples presented higher Faradaic efficiencies(FE)for CO and relatively suppressed H2 evolution than the parent Cu2O nanospheres due to the combination of Ag with Cu2O in the former.Notably,the highest CO evolution rate was achieved with Ago.12/Cu2O due to the larger electroactive surface area furnished by the hierarchical structure.The same hier-archical flower-like structure was also obtained for the Auo./Cu2O composite,where the FEco(10%)was even higher than that of Ago.12/Cu2O.Importantly,the results reveal that Ago.12/Cu2O and Auo./Cu2O both exhibit remarkably improved stability relative to Cu2O.This study presents a facile method of developing hierarchical metal-oxide composites as fficient and stable electrocatalysts for the electrochemical reduction of CO2.展开更多
In constructing a smart court,to provide intelligent assistance for achieving more efficient,fair,and explainable trial proceedings,we propose a full-process intelligent trial system(FITS).In the proposed FITS,we intr...In constructing a smart court,to provide intelligent assistance for achieving more efficient,fair,and explainable trial proceedings,we propose a full-process intelligent trial system(FITS).In the proposed FITS,we introduce essential tasks for constructing a smart court,including information extraction,evidence classification,question generation,dialogue summarization,judgment prediction,and judgment document generation.Specifically,the preliminary work involves extracting elements from legal texts to assist the judge in identifying the gist of the case efficiently.With the extracted attributes,we can justify each piece of evidence’s validity by establishing its consistency across all evidence.During the trial process,we design an automatic questioning robot to assist the judge in presiding over the trial.It consists of a finite state machine representing procedural questioning and a deep learning model for generating factual questions by encoding the context of utterance in a court debate.Furthermore,FITS summarizes the controversy focuses that arise from a court debate in real time,constructed under a multi-task learning framework,and generates a summarized trial transcript in the dialogue inspectional summarization(DIS)module.To support the judge in making a decision,we adopt first-order logic to express legal knowledge and embed it in deep neural networks(DNNs)to predict judgments.Finally,we propose an attentional and counterfactual natural language generation(AC-NLG)to generate the court’s judgment.展开更多
The electrochemical conversion of CO_(2)-H_(2)O into CO-H_(2) using renewable energy is a promising technique for clean syngas production.Low-cost electrocatalysts to produce tunable syngas with a potential-independen...The electrochemical conversion of CO_(2)-H_(2)O into CO-H_(2) using renewable energy is a promising technique for clean syngas production.Low-cost electrocatalysts to produce tunable syngas with a potential-independent CO/H_(2) ratio are highly desired.Herein,a series of N-doped carbon nanotubes encapsulating binary alloy nanoparticles(MxNi-NCNT,M=Fe,Co)were successfully fabricated through the co-pyrolysis of melamine and metal precursors.The MxNi-NCNT samples exhibited bamboo-like nanotubular structures with a large specific surface area and high degree of graphitization.Their electrocatalytic performance for syngas production can be tuned by changing the alloy compositions and modifying the electronic structure of the carbon nanotube through the encapsulated metal nanoparticles.Consequently,syngas with a wide range of CO/H_(2) ratios,from 0.5:1 to 3.4:1,can be produced on MxNi-NCNT.More importantly,stable CO/H_(2) ratios of 2:1 and 1.5:1,corresponding to the ratio to produce biofuels by syngas fermentation,could be realized on Co1Ni-NCNT and Co2Ni-NCNT,respectively,over a potential window of-0.8 to-1.2 V versus the reversible hydrogen electrode.Our work provides an approach to develop low-cost and potential-independent electrocatalysts to effectively produce syngas with an adjustable CO/H_(2) ratio from electrochemical CO_(2) reduction.展开更多
Electrochemical reduction of CO2 has the benefit of turning greenhouse gas emissions into useful resources. We performed a comparative study of the electrochemical reduction of CO2 on stepped Pb(211) and Sn(112) surfa...Electrochemical reduction of CO2 has the benefit of turning greenhouse gas emissions into useful resources. We performed a comparative study of the electrochemical reduction of CO2 on stepped Pb(211) and Sn(112) surfaces based on the results of density functional theory slab calculations. We mapped out the potential energy profiles for electrochemical reduction of CO2 to formate and other possible products on both surfaces. Our results show that the first step is the formation of the adsorbed formate(HCOO*) species through an Eley-Rideal mechanism. The formate species can be reduced to HCOO- through a oneelectron reduction in basic solution, which produces formic acid as the predominant product. The respective potentials of forming HCOO* are predicted to be -0.72 and -0.58 V on Pb and Sn. Higher overpotentials make other reaction pathways accessible, leading to different products. On Sn(112), CO and CH4 can be generated at -0.65 V following formate formation. In contrast, the limiting potential to access alternative reaction channels on Pb(211) is -1.33 V, significantly higher than that of Sn.展开更多
TheNH_(3)-TPDcharacterization wasconducted to confirm that the acidity of Mo-Fe/HZSM-5 zeolite could be selectively modified via the glow discharge plasma treatment.The plasma catalyst treatment could totally change t...TheNH_(3)-TPDcharacterization wasconducted to confirm that the acidity of Mo-Fe/HZSM-5 zeolite could be selectively modified via the glow discharge plasma treatment.The plasma catalyst treatment could totally change the distribution of aromatic products with higher methane conversion compared to the untreated catalyst.Some polycyclic aromatics such as anthracene,pyrene and phenanthrene were also produced over the plasma treated catalyst,in addition to benzene,toluene and naphthalene,which were normally obtained over the untreated catalyst.展开更多
基金the National Key Research and Development Program of China(No.2016YFB0600900)the National Natural Science Foundation of China(Nos.21676194 and 21873067)for their support。
文摘The catalytic conversion of CO2 to CO via a reverse water gas shift(RWGS)reaction followed by well-established synthesis gas conversion technologies may provide a potential approach to convert CO2 to valuable chemicals and fuels.However,this reaction is mildly endothermic and competed by a strongly exothermic CO2 methanation reaction at low temperatures.Therefore,the improvement in the low-temperature activities and selectivity of the RWGS reaction is a key challenge for catalyst designs.We reviewed recent advances in the design strategies of supported metal catalysts for enhancing the activity of CO2 conversion and its selectivity to CO.These strategies include varying support,tuning metal–support interactions,adding reducible transition metal oxide promoters,forming bimetallic alloys,adding alkali metals,and enveloping metal particles.These advances suggest that enhancing CO2 adsorption and facilitating CO desorption are key factors to enhance CO2 conversion and CO selectivity.This short review may provide insights into future RWGS catalyst designs and optimization.
基金the National Natural Science Foundation of China(Nos.21873067 and 21576204).
文摘Propane oxidative dehydrogenation(ODH)is an energy-efficient approach to produce propylene.However,ODH suff ers from low propylene selectivity due to a relatively higher activation barrier for propylene formation compared with that for further oxidation.In this work,calculations based on density functional theory were performed to map out the reaction pathways of propane ODH on the surfaces(001)and(010)of nickel oxide hydroxide(NiOOH).Results show that propane is physisorbed on both surfaces and produces propylene through a two-step radical dehydrogenation process.The relatively low activation barriers of propane dehydrogenation on the NiOOH surfaces make the NiOOH-based catalysts promising for propane ODH.By contrast,the weak interaction between the allylic radical and the surface leads to a high activation barrier for further propylene oxidation.These results suggest that the catalysts based on NiOOH can be active and selective for the ODH of propane toward propylene.
基金This study was supported by the National Natural Science Foundation of China （NSFC）, the State Key Research Projects for Fundamental Science （Nos. 2007CB936200, 2007CB936202, and 2009CB623703） of Ministry of Science and Technology of China （MOST）, and Natural Science Foundation （NSF） of Jiangsu Province of China.
文摘Although possible non-homogeneous strain effects in semiconductors have been investigated for over a half century and the strain-gradient can be over 1% per micrometer in flexible nanostructures, we still lack an understanding of their influence on energy bands. Here we conduct a systematic cathodoluminescence spectroscopy study of the strain-gradient induced exciton energy shift in elastically curved CdS nanowires at low temperature, and find that the red-shift of the exciton energy in the curved nanowires is proportional to the strain-gradient, an index of lattice distortion. Density functional calculations show the same trend of band gap reduction in curved nanostructures and reveal the underlying mechanism. The significant linear straingradient effect on the band gap of semiconductors should shed new light on ways to tune optical-electronic properties in nanoelectronics.
基金We are grateful to the Analysis and Test Center of Tianjin University for providing XRD,SEM,and TEM characterization.We also acknowledge the National Natural Science Foundation of China(Grant Nos.21576204 and 21206117)for financial support.
文摘Novel,hierarchical,flower-like Ag/Cu2O and Au/Cu2O nanostructures were successfully fabricated and applied as efficient electrocatalysts for the electrochemical reduction of CO2.Cu2O nanospheres with a uniform size of^180 nm were initially synthesized.Thereafter,Cu2O was used as a sacrificial template to prepare a series of Ag/Cu2O composites through galvanic replacement.By varying the Ag/Cu atomic ratio,Ago.12/Cu2O,having a hierarchical,flower-like nanostructure with intersecting Ag nanoflakes encompassing an inner Cu2O sphere,was prepared.The as-prepared Ag/Cu2O samples presented higher Faradaic efficiencies(FE)for CO and relatively suppressed H2 evolution than the parent Cu2O nanospheres due to the combination of Ag with Cu2O in the former.Notably,the highest CO evolution rate was achieved with Ago.12/Cu2O due to the larger electroactive surface area furnished by the hierarchical structure.The same hier-archical flower-like structure was also obtained for the Auo./Cu2O composite,where the FEco(10%)was even higher than that of Ago.12/Cu2O.Importantly,the results reveal that Ago.12/Cu2O and Auo./Cu2O both exhibit remarkably improved stability relative to Cu2O.This study presents a facile method of developing hierarchical metal-oxide composites as fficient and stable electrocatalysts for the electrochemical reduction of CO2.
基金supported by the Key R&D Projects of the Ministry of Science and Technology of China(No.2020YFC0832500)the National Key Research and Development Program of China(No.2018AAA0101900)+3 种基金the National Social Science Foundation of China(No.20&ZD047)the National Natural Science Foundation of China(Nos.61625107 and 62006207)the Key R&D Project of Zhejiang Province,China(No.2020C01060)the Fundamental Research Funds for the Central Universities,China(Nos.LQ21F020020 and 2020XZA202)。
文摘In constructing a smart court,to provide intelligent assistance for achieving more efficient,fair,and explainable trial proceedings,we propose a full-process intelligent trial system(FITS).In the proposed FITS,we introduce essential tasks for constructing a smart court,including information extraction,evidence classification,question generation,dialogue summarization,judgment prediction,and judgment document generation.Specifically,the preliminary work involves extracting elements from legal texts to assist the judge in identifying the gist of the case efficiently.With the extracted attributes,we can justify each piece of evidence’s validity by establishing its consistency across all evidence.During the trial process,we design an automatic questioning robot to assist the judge in presiding over the trial.It consists of a finite state machine representing procedural questioning and a deep learning model for generating factual questions by encoding the context of utterance in a court debate.Furthermore,FITS summarizes the controversy focuses that arise from a court debate in real time,constructed under a multi-task learning framework,and generates a summarized trial transcript in the dialogue inspectional summarization(DIS)module.To support the judge in making a decision,we adopt first-order logic to express legal knowledge and embed it in deep neural networks(DNNs)to predict judgments.Finally,we propose an attentional and counterfactual natural language generation(AC-NLG)to generate the court’s judgment.
基金funded by the National Natural Science Foundation of China(Grant Nos.21873067,21206117).
文摘The electrochemical conversion of CO_(2)-H_(2)O into CO-H_(2) using renewable energy is a promising technique for clean syngas production.Low-cost electrocatalysts to produce tunable syngas with a potential-independent CO/H_(2) ratio are highly desired.Herein,a series of N-doped carbon nanotubes encapsulating binary alloy nanoparticles(MxNi-NCNT,M=Fe,Co)were successfully fabricated through the co-pyrolysis of melamine and metal precursors.The MxNi-NCNT samples exhibited bamboo-like nanotubular structures with a large specific surface area and high degree of graphitization.Their electrocatalytic performance for syngas production can be tuned by changing the alloy compositions and modifying the electronic structure of the carbon nanotube through the encapsulated metal nanoparticles.Consequently,syngas with a wide range of CO/H_(2) ratios,from 0.5:1 to 3.4:1,can be produced on MxNi-NCNT.More importantly,stable CO/H_(2) ratios of 2:1 and 1.5:1,corresponding to the ratio to produce biofuels by syngas fermentation,could be realized on Co1Ni-NCNT and Co2Ni-NCNT,respectively,over a potential window of-0.8 to-1.2 V versus the reversible hydrogen electrode.Our work provides an approach to develop low-cost and potential-independent electrocatalysts to effectively produce syngas with an adjustable CO/H_(2) ratio from electrochemical CO_(2) reduction.
基金supported by the National Natural Sciences Foundation of China(21373148,21206117)
文摘Electrochemical reduction of CO2 has the benefit of turning greenhouse gas emissions into useful resources. We performed a comparative study of the electrochemical reduction of CO2 on stepped Pb(211) and Sn(112) surfaces based on the results of density functional theory slab calculations. We mapped out the potential energy profiles for electrochemical reduction of CO2 to formate and other possible products on both surfaces. Our results show that the first step is the formation of the adsorbed formate(HCOO*) species through an Eley-Rideal mechanism. The formate species can be reduced to HCOO- through a oneelectron reduction in basic solution, which produces formic acid as the predominant product. The respective potentials of forming HCOO* are predicted to be -0.72 and -0.58 V on Pb and Sn. Higher overpotentials make other reaction pathways accessible, leading to different products. On Sn(112), CO and CH4 can be generated at -0.65 V following formate formation. In contrast, the limiting potential to access alternative reaction channels on Pb(211) is -1.33 V, significantly higher than that of Sn.
基金The support from the State Key Development Program for Basic Research of China(Grant No.2005CB221406)the National Natural Science Foundation of China(Grant No.20490203)are much appreciated.
文摘TheNH_(3)-TPDcharacterization wasconducted to confirm that the acidity of Mo-Fe/HZSM-5 zeolite could be selectively modified via the glow discharge plasma treatment.The plasma catalyst treatment could totally change the distribution of aromatic products with higher methane conversion compared to the untreated catalyst.Some polycyclic aromatics such as anthracene,pyrene and phenanthrene were also produced over the plasma treated catalyst,in addition to benzene,toluene and naphthalene,which were normally obtained over the untreated catalyst.
