ZnO-based catalysts have been intensively studied because of their extraordinary performance in lower olefin synthesis,methanol synthesis and water-gas shift reactions.However,how ZnO catalyzes these reactions are sti...ZnO-based catalysts have been intensively studied because of their extraordinary performance in lower olefin synthesis,methanol synthesis and water-gas shift reactions.However,how ZnO catalyzes these reactions are still not well understood.Herein,we investigate the activations of CO_(2),O_(2)and CO on single crystalline ZnO polar surfaces at room temperature,through in-situ near-ambient-pressure X-ray photoelectron spectroscopy(NAP-XPS).It is revealed that O_(2)and CO_(2)can undergo chemisorption on ZnO polar surfaces at elevated pressures.On the ZnO(0001)surface,molecular CO_(2)(O_(2))can chemically interact with the top layer Zn atoms,leading to the formation of CO_(2)^(δ-)(O_(2)^(δ-))or partially dissociative atomic oxygen(O-)and hence the electron depletion layer in ZnO.Therefore,an apparent upward band-bending in ZnO(0001)is observed under the CO_(2)and O_(2)exposure.On the ZnO(0001)surface,the molecular chemisorbed CO_(2)(O_(2))mainly bond to the surface oxygen vacancies,which also results in an upward bandbending in ZnO(0001).In contrast,no band-bending is observed for both ZnO polar surfaces upon CO exposure.The electron-acceptor nature of the surface bounded molecules/atoms is responsible for the reversible binding energy shift of Zn 2 p_(3/2)and O 1 s in ZnO.Our findings can shed light on the fundamental understandings of CO_(2)and O_(2)activation on ZnO surfaces,especially the role of ZnO in heterogeneous catalytic reactions.展开更多
Organic anode materials have attracted considerable interest owing to their high tunability by adopting various active functional groups.However,the interaction mechanisms between the alkali metals and the active func...Organic anode materials have attracted considerable interest owing to their high tunability by adopting various active functional groups.However,the interaction mechanisms between the alkali metals and the active functional groups in host materials have been rarely studied systematically.Here,a widely used organic semiconductor of perylene-3,4,9,10-tetracarboxylic diimide(PTCDI)was selected as a model system to investigate how alkali metals interact with imide functional groups and induce changes in chemical and electronic structures of PTCDI.The interaction at the alkali/PTCDI interface was probed by in-situ X-ray photoelectron spectroscopy(XPS),ultraviolet photoelectron spectroscopy(UPS),synchrotron-based near edge X-ray absorption fine structure(NEXAFS),and corroborated by density functional theory(DFT)calculations.Our results indicate that the alkali metal replaces the hydrogen atoms in the imide group and interact with the imide nitrogen of PTCDI.Electron transfer induced gap states and downward band-bending like effects are identified on the alkali-deposited PTCDI surface.It was found that Na shows a stronger electron transfer effect than Li.Such a model study of alkali insertion/intercalation in PTCDI gives insights for the exploration of the potential host materials for alkali storage applications.展开更多
Nitrogen fixation is a vital process for both nature and industry.Whereas the nitrogenase can reduce nitrogen in ambient environment in nature,the industrialized Haber-Bosch process is a high temperature and high-pres...Nitrogen fixation is a vital process for both nature and industry.Whereas the nitrogenase can reduce nitrogen in ambient environment in nature,the industrialized Haber-Bosch process is a high temperature and high-pressure process.Since the discovery of the first dinitrogen complex in 1965,many dinitrogen complexes are prepared in a homogeneous solution to mimic the nitrogenase enzyme in nature.However,studies of the heterogeneous process on surface are rarely addressed.Moreover,molecular scale characterization for such dinitrogen complex is lacking.Here,we present a simple model system to investigate,at the single-molecule level,the binding of dinitrogen on a surface confined iron phthalocyanine(FePc)monolayer through the combination of in-situ low-temperature scanning tunneling microscopy(LT-STM)and X-ray photoelectron spectroscopy(XPS)measurements.The iron center in FePc molecule deposited on Au(111)and highly oriented pyrolytic graphite(HOPG)surface can adsorb dinitrogen molecule at room temperature and low pressure.A comparative study reveals that the adsorption behaviors of FePc on these two different substrates are identical.Chemical bond is formed between the dinitrogen and the Fe atom in the FePc molecule,which greatly modifies the electronic structure of FePc.The bonding is reversible and can be manipulated by applying bias using a STM tip or by thermal annealing.展开更多
基金financial supports from the National Natural Science Foundation of China(Grant no.91645102 and 22002031)the Singapore National Research Foundation under the grant of NRF2017NRF-NSFC001-007the NUS Flagship Green Energy Programme。
文摘ZnO-based catalysts have been intensively studied because of their extraordinary performance in lower olefin synthesis,methanol synthesis and water-gas shift reactions.However,how ZnO catalyzes these reactions are still not well understood.Herein,we investigate the activations of CO_(2),O_(2)and CO on single crystalline ZnO polar surfaces at room temperature,through in-situ near-ambient-pressure X-ray photoelectron spectroscopy(NAP-XPS).It is revealed that O_(2)and CO_(2)can undergo chemisorption on ZnO polar surfaces at elevated pressures.On the ZnO(0001)surface,molecular CO_(2)(O_(2))can chemically interact with the top layer Zn atoms,leading to the formation of CO_(2)^(δ-)(O_(2)^(δ-))or partially dissociative atomic oxygen(O-)and hence the electron depletion layer in ZnO.Therefore,an apparent upward band-bending in ZnO(0001)is observed under the CO_(2)and O_(2)exposure.On the ZnO(0001)surface,the molecular chemisorbed CO_(2)(O_(2))mainly bond to the surface oxygen vacancies,which also results in an upward bandbending in ZnO(0001).In contrast,no band-bending is observed for both ZnO polar surfaces upon CO exposure.The electron-acceptor nature of the surface bounded molecules/atoms is responsible for the reversible binding energy shift of Zn 2 p_(3/2)and O 1 s in ZnO.Our findings can shed light on the fundamental understandings of CO_(2)and O_(2)activation on ZnO surfaces,especially the role of ZnO in heterogeneous catalytic reactions.
基金The authors acknowledge the financial support from Singapore MOE Tier II grant R143-000-A29-112,Academic Research Fund Tie I grant RG104/18,and the National Research Foundation under the grant of NRF2017NRF-NSFC001-007the computing resources from National Supercomputing Centre Singapore.
文摘Organic anode materials have attracted considerable interest owing to their high tunability by adopting various active functional groups.However,the interaction mechanisms between the alkali metals and the active functional groups in host materials have been rarely studied systematically.Here,a widely used organic semiconductor of perylene-3,4,9,10-tetracarboxylic diimide(PTCDI)was selected as a model system to investigate how alkali metals interact with imide functional groups and induce changes in chemical and electronic structures of PTCDI.The interaction at the alkali/PTCDI interface was probed by in-situ X-ray photoelectron spectroscopy(XPS),ultraviolet photoelectron spectroscopy(UPS),synchrotron-based near edge X-ray absorption fine structure(NEXAFS),and corroborated by density functional theory(DFT)calculations.Our results indicate that the alkali metal replaces the hydrogen atoms in the imide group and interact with the imide nitrogen of PTCDI.Electron transfer induced gap states and downward band-bending like effects are identified on the alkali-deposited PTCDI surface.It was found that Na shows a stronger electron transfer effect than Li.Such a model study of alkali insertion/intercalation in PTCDI gives insights for the exploration of the potential host materials for alkali storage applications.
基金Authors acknowledge the financial support from Singapore National Research Foundation under NRF2017NRF-NSFC001-007Singapore MOE grant of MOE2019-T2-1-002 and NUS Flagship Green Energy Program.
文摘Nitrogen fixation is a vital process for both nature and industry.Whereas the nitrogenase can reduce nitrogen in ambient environment in nature,the industrialized Haber-Bosch process is a high temperature and high-pressure process.Since the discovery of the first dinitrogen complex in 1965,many dinitrogen complexes are prepared in a homogeneous solution to mimic the nitrogenase enzyme in nature.However,studies of the heterogeneous process on surface are rarely addressed.Moreover,molecular scale characterization for such dinitrogen complex is lacking.Here,we present a simple model system to investigate,at the single-molecule level,the binding of dinitrogen on a surface confined iron phthalocyanine(FePc)monolayer through the combination of in-situ low-temperature scanning tunneling microscopy(LT-STM)and X-ray photoelectron spectroscopy(XPS)measurements.The iron center in FePc molecule deposited on Au(111)and highly oriented pyrolytic graphite(HOPG)surface can adsorb dinitrogen molecule at room temperature and low pressure.A comparative study reveals that the adsorption behaviors of FePc on these two different substrates are identical.Chemical bond is formed between the dinitrogen and the Fe atom in the FePc molecule,which greatly modifies the electronic structure of FePc.The bonding is reversible and can be manipulated by applying bias using a STM tip or by thermal annealing.
