The physicochemical properties of Pd and Pd-Pt catalysts which possess different Ce doping position were investigated by techniques of TEM, XRD, N2 adsorption-desorption, XPS and FT-IR. The catalytic performance for m...The physicochemical properties of Pd and Pd-Pt catalysts which possess different Ce doping position were investigated by techniques of TEM, XRD, N2 adsorption-desorption, XPS and FT-IR. The catalytic performance for methanol total oxidation was examined to study the effects of Ce adding position.CeO2-Al2 O3-TiO2（CAT） catalysts that Ce is directly introduced into support show higher reactivity and CO2 selectivity than CeO2/Al2 O3-TiO2（Ce/AT） samples in which Ce is loaded by impregnation method.The characterization results reveal that the Ce doping position does not cause obvious otherness of basic crystalline phase and mesoporous structure of support. However, the Ce doping position affects the pore shapes of support and then influences the pore diameter. CAT catalysts possess more abundant adsorbed oxygen and more Ti3＋ can transform the more gaseous oxygen into the active oxygen species on the catalyst surface, which is beneficial to the reaction. The Al-O-Ti bridges in CAT facilitate the cooperation of Al and Ti species, which further speeds up the reaction rate.展开更多
The excellent oxygen reduction reaction(ORR)activity of Fe–N–C catalysts in acidic media makes them potential for low-cost proton exchange membrane fuel cells.In recent years,it has been shown that heteroatoms(B,O,S...The excellent oxygen reduction reaction(ORR)activity of Fe–N–C catalysts in acidic media makes them potential for low-cost proton exchange membrane fuel cells.In recent years,it has been shown that heteroatoms(B,O,S,P,Cl,F,etc.)can be used as electron-withdrawing groups to modulate the planar structure and electron distribution of the Fe–Nx active sites to achieve simultaneous improvement of catalytic activity and stability.However,the optimal location of the heteroatoms remains unclear.Here,taking chalcogen heteroatoms(S and Se)as an example,we control the doping positions and investigate their effect on the ORR performance of the Fe–N–C catalysts.The first coordination shell of the iron single atom is identified as the optimal doping position.The optimized catalysts Fe–N_(3)Se_(1)/NC and Fe–N_(3)Se_(1)/NC demonstrate improved activity and stability in both half cells and fuel cells.This work provides insights into the enhancement mechanism of heteroatom doping in single-atom catalysts.展开更多
The extinction ratio （ER） ofa Mach-Zehnder-interference （MZI） based silicon optical modulator can be strongly influenced by carrier absorption. Moreover, different doping positions can induce different distributio...The extinction ratio （ER） ofa Mach-Zehnder-interference （MZI） based silicon optical modulator can be strongly influenced by carrier absorption. Moreover, different doping positions can induce different distributions of injected carriers, leading to different ERs. This effect has been experimentally investigated based on the devices fabricated on silicon-on-insulator （SOl） by using a 0.18μm CMOS process. Our experiments indicate that a device with a doping position of about 0.5μm away from the edge of the rib waveguide has optimal ER.展开更多
基金Project supported by the Key Program of National Natural Science Foundation of China(21336006)the Shanxi Province Scientific and Technological Project(20140313002-2)
文摘The physicochemical properties of Pd and Pd-Pt catalysts which possess different Ce doping position were investigated by techniques of TEM, XRD, N2 adsorption-desorption, XPS and FT-IR. The catalytic performance for methanol total oxidation was examined to study the effects of Ce adding position.CeO2-Al2 O3-TiO2（CAT） catalysts that Ce is directly introduced into support show higher reactivity and CO2 selectivity than CeO2/Al2 O3-TiO2（Ce/AT） samples in which Ce is loaded by impregnation method.The characterization results reveal that the Ce doping position does not cause obvious otherness of basic crystalline phase and mesoporous structure of support. However, the Ce doping position affects the pore shapes of support and then influences the pore diameter. CAT catalysts possess more abundant adsorbed oxygen and more Ti3＋ can transform the more gaseous oxygen into the active oxygen species on the catalyst surface, which is beneficial to the reaction. The Al-O-Ti bridges in CAT facilitate the cooperation of Al and Ti species, which further speeds up the reaction rate.
基金supported by the National Key Research and Development Program of China(grant No.2021YFB4000601)Natural Science Foundation of Beijing Municipality(grant No.Z200012)+1 种基金National Natural Science Foundation of China(grant No.21975010,U21A20328)the China Postdoctoral Science Foundation(grant No.2022M720013).
文摘The excellent oxygen reduction reaction(ORR)activity of Fe–N–C catalysts in acidic media makes them potential for low-cost proton exchange membrane fuel cells.In recent years,it has been shown that heteroatoms(B,O,S,P,Cl,F,etc.)can be used as electron-withdrawing groups to modulate the planar structure and electron distribution of the Fe–Nx active sites to achieve simultaneous improvement of catalytic activity and stability.However,the optimal location of the heteroatoms remains unclear.Here,taking chalcogen heteroatoms(S and Se)as an example,we control the doping positions and investigate their effect on the ORR performance of the Fe–N–C catalysts.The first coordination shell of the iron single atom is identified as the optimal doping position.The optimized catalysts Fe–N_(3)Se_(1)/NC and Fe–N_(3)Se_(1)/NC demonstrate improved activity and stability in both half cells and fuel cells.This work provides insights into the enhancement mechanism of heteroatom doping in single-atom catalysts.
基金Project Supported by the Natural Basic Research Program of China(No.2007CB6I3405)the NationaI Natural Science Foundation of China(Nos.60977043,60808035)
文摘The extinction ratio （ER） ofa Mach-Zehnder-interference （MZI） based silicon optical modulator can be strongly influenced by carrier absorption. Moreover, different doping positions can induce different distributions of injected carriers, leading to different ERs. This effect has been experimentally investigated based on the devices fabricated on silicon-on-insulator （SOl） by using a 0.18μm CMOS process. Our experiments indicate that a device with a doping position of about 0.5μm away from the edge of the rib waveguide has optimal ER.
