The determination of catalytically active sites is crucial for the design of efficient and stable catalysts toward desired reactions.However,the complexity of supported noble metal catalysts has led to controversy ove...The determination of catalytically active sites is crucial for the design of efficient and stable catalysts toward desired reactions.However,the complexity of supported noble metal catalysts has led to controversy over the locations of catalytically active sites(e.g.,metal,support,and metal/support interface).Here we develop a structurally controllable catalyst system(Pd/SBA-15)to reveal the catalytic active sites for the selective hydrogenation of ketones to alcohol using acetophenone hydrogenation as model reaction.Systematic investigations demonstrated that unsupported Pd nanocrystals have no catalytic activity for acetophenone hydrogenation.However,oxidized Pd species were catalytically highly active for acetophenone hydrogenation.The catalytic activity decreased with the decreased oxidation state of Pd.This work provides insights into the hydrogenation mechanism of ketones but also other unsaturated compounds containing polar bonds,e.g.,nitrobenzene,N-benzylidene-benzylamine,and carbon dioxide.展开更多
The interface between metal nanoparticles(NPs)and support plays a vital role in catalysis because both electron and atom exchanges occur across the metal-support interface.However,the rational design of interfacial st...The interface between metal nanoparticles(NPs)and support plays a vital role in catalysis because both electron and atom exchanges occur across the metal-support interface.However,the rational design of interfacial structure facilitating the charge transfer between the neighboring parts remains a challenge.Herein,a guided nucleation strategy based on redox reaction between noble metal precursor and supportsurface is introduced to construct epitaxial interfaces between Pt NPs and CeO2 support.The Pt/CeO2 catalyst exhibits near room temperature catalytic activity for CO oxidation that is benefited from the well-defined interface structure facilitating charge transfer from CeO2 support to Pt NPs.Meanwhile,this general approach based on support-surface-induced-nucleation was successfully extended to synthesize Pd and Cu nanocatalysts on CeO2,demonstrating its universal and feasible characteristics.This work is an important step towards developing highly active supported metal catalysts by engineering their interfaces.展开更多
The adhesion and wetting of non-reactive liquid metals with solid ionocovalent oxides are studied on the basis of the experimental work of adhesion W data obtained with the sessile drop method.An analysis of the exper...The adhesion and wetting of non-reactive liquid metals with solid ionocovalent oxides are studied on the basis of the experimental work of adhesion W data obtained with the sessile drop method.An analysis of the experimental W values of different liquid metals on various solid oxides is first performed to evidence the de- pendence of the work of adhesion of a metal/oxide system on the electron density of the metal and on the thermodynamic stability of the oxide.An electronic model is then proposed to describe the microscopic mech- anism of metal-oxide interactions.Based on the model,the contact angle and the work of adhesion of different liquid metals on various solid oxides can be interpreted and estimated,and their correlations to the various physical quantities of the oxides can be easily deduced.The basic consideration of the model is that the adhe- sion between a metal and an oxide is assured by the electron transfer from the metal into the oxide valence band which is not completely filled of electrons at high temperatures,and is enhanced when this electron trans- fer at the metal/oxide interface is intensified.The influence of interface defects on the wetting and adhesion is suggested and discussed.展开更多
La0.67Ca0.33MnO3 thin films are fabricated on fluorine-doped tin oxide conducting glass substrates by a pulsed laser deposition technique with SrTiO3 used as a buffer layer. The current-voltage characteristics of the ...La0.67Ca0.33MnO3 thin films are fabricated on fluorine-doped tin oxide conducting glass substrates by a pulsed laser deposition technique with SrTiO3 used as a buffer layer. The current-voltage characteristics of the heterojunetions exhibit an asymmetric and resistance switching behaviour. A homogeneous interface-type conduction mechanism is also reported using impedance spectroscopy. The spatial homogeneity of the charge carrier distribution leads to field- induced potential-barrier change at the Au-La0.67Ca0.33MnO3 interface and a concomitant resistance switching effect. The ratio of the high resistance state to the low resistance state is found to be as high as 1.3 x 10^4% by simulating the AC electric field. This colossal resistance switching effect will greatly improve the signal-to-noise ratio in nonvolatile memory applications.展开更多
The resistive switching properties in amorphous Pr0.67Sr0.33MnO3 films deposited by pulsed laser deposition are investigated.Reproducible and bipolar counter-8-shape and 8-shape switching behaviours of Au/Pr0.67Sr0.33...The resistive switching properties in amorphous Pr0.67Sr0.33MnO3 films deposited by pulsed laser deposition are investigated.Reproducible and bipolar counter-8-shape and 8-shape switching behaviours of Au/Pr0.67Sr0.33MnO3 /F：SnO2 junctions are obtained at room temperature.Dramatically,the coexistence of two switching polarities could be reversibly adjusted by an applied voltage range.The results allocated those two switching types to areas of different defect densities beneath the same electrode.The migration of oxygen vacancies and the trapping effect of electrons under an applied electric field play an important role.An interface-effect-related resistance switching is proposed in an amorphous Pr0.67Sr0.33MnO3-based memory cell.展开更多
基金supported by the National Natural Science Foundation of China(Nos.92261207,21890752,and 22002126)。
文摘The determination of catalytically active sites is crucial for the design of efficient and stable catalysts toward desired reactions.However,the complexity of supported noble metal catalysts has led to controversy over the locations of catalytically active sites(e.g.,metal,support,and metal/support interface).Here we develop a structurally controllable catalyst system(Pd/SBA-15)to reveal the catalytic active sites for the selective hydrogenation of ketones to alcohol using acetophenone hydrogenation as model reaction.Systematic investigations demonstrated that unsupported Pd nanocrystals have no catalytic activity for acetophenone hydrogenation.However,oxidized Pd species were catalytically highly active for acetophenone hydrogenation.The catalytic activity decreased with the decreased oxidation state of Pd.This work provides insights into the hydrogenation mechanism of ketones but also other unsaturated compounds containing polar bonds,e.g.,nitrobenzene,N-benzylidene-benzylamine,and carbon dioxide.
基金supported by the National Natural Science Foundation of China(Nos.51771047,51525101,U1602275,51601119)the Fundamental Research Funds for the Central Universities(N180204014)+1 种基金the Key Lab for ATM of Northeastern University(China)the Natural Science Foundation of Shenzhen University(No.2019006).
文摘The interface between metal nanoparticles(NPs)and support plays a vital role in catalysis because both electron and atom exchanges occur across the metal-support interface.However,the rational design of interfacial structure facilitating the charge transfer between the neighboring parts remains a challenge.Herein,a guided nucleation strategy based on redox reaction between noble metal precursor and supportsurface is introduced to construct epitaxial interfaces between Pt NPs and CeO2 support.The Pt/CeO2 catalyst exhibits near room temperature catalytic activity for CO oxidation that is benefited from the well-defined interface structure facilitating charge transfer from CeO2 support to Pt NPs.Meanwhile,this general approach based on support-surface-induced-nucleation was successfully extended to synthesize Pd and Cu nanocatalysts on CeO2,demonstrating its universal and feasible characteristics.This work is an important step towards developing highly active supported metal catalysts by engineering their interfaces.
基金This work was supported by the National Natural Science Foundation of China(No.12075243)the National Key Research and Development Program of China(No.2017YFA0402800)。
文摘The adhesion and wetting of non-reactive liquid metals with solid ionocovalent oxides are studied on the basis of the experimental work of adhesion W data obtained with the sessile drop method.An analysis of the experimental W values of different liquid metals on various solid oxides is first performed to evidence the de- pendence of the work of adhesion of a metal/oxide system on the electron density of the metal and on the thermodynamic stability of the oxide.An electronic model is then proposed to describe the microscopic mech- anism of metal-oxide interactions.Based on the model,the contact angle and the work of adhesion of different liquid metals on various solid oxides can be interpreted and estimated,and their correlations to the various physical quantities of the oxides can be easily deduced.The basic consideration of the model is that the adhe- sion between a metal and an oxide is assured by the electron transfer from the metal into the oxide valence band which is not completely filled of electrons at high temperatures,and is enhanced when this electron trans- fer at the metal/oxide interface is intensified.The influence of interface defects on the wetting and adhesion is suggested and discussed.
基金supported by the National Natural Science Foundation of China (Grant No. 60976016)the Program for Innovative Research Team in Science and Technology in University of Henan Province (IRTSTHN),China (Grant No. 2012IRTSTHN004)the Research Program of Henan University, China (Grant No. SBGJ090503)
文摘La0.67Ca0.33MnO3 thin films are fabricated on fluorine-doped tin oxide conducting glass substrates by a pulsed laser deposition technique with SrTiO3 used as a buffer layer. The current-voltage characteristics of the heterojunetions exhibit an asymmetric and resistance switching behaviour. A homogeneous interface-type conduction mechanism is also reported using impedance spectroscopy. The spatial homogeneity of the charge carrier distribution leads to field- induced potential-barrier change at the Au-La0.67Ca0.33MnO3 interface and a concomitant resistance switching effect. The ratio of the high resistance state to the low resistance state is found to be as high as 1.3 x 10^4% by simulating the AC electric field. This colossal resistance switching effect will greatly improve the signal-to-noise ratio in nonvolatile memory applications.
基金Project supported by the National Natural Science Foundation of China (Grant No. 60976016)the Program for Innovative Research Team in Science and Technology in University of Henan Province (IRTSTUHN),China (Grant No. 2012IRTSTHN004)the Foundation Co-established by the Province and the Ministry in Henan University,China (Grant No. SBGJ090503)
文摘The resistive switching properties in amorphous Pr0.67Sr0.33MnO3 films deposited by pulsed laser deposition are investigated.Reproducible and bipolar counter-8-shape and 8-shape switching behaviours of Au/Pr0.67Sr0.33MnO3 /F：SnO2 junctions are obtained at room temperature.Dramatically,the coexistence of two switching polarities could be reversibly adjusted by an applied voltage range.The results allocated those two switching types to areas of different defect densities beneath the same electrode.The migration of oxygen vacancies and the trapping effect of electrons under an applied electric field play an important role.An interface-effect-related resistance switching is proposed in an amorphous Pr0.67Sr0.33MnO3-based memory cell.
