MnO_x/Al_2O_3 and MnO_x/ZrO_2-Al_2O_3 catalysts were prepared by incipientwetness impregnation of Mn(CH_3COO)_2 on the corresponding supports, followed by thecharacterization using X-ray diffraction (XRD), temperature...MnO_x/Al_2O_3 and MnO_x/ZrO_2-Al_2O_3 catalysts were prepared by incipientwetness impregnation of Mn(CH_3COO)_2 on the corresponding supports, followed by thecharacterization using X-ray diffraction (XRD), temperature programmed reduction (TPR) and BETsurface area techniques. The result shows the BET surface area of ZrO_2-Al_2O_3 is lower than thatof Al_2O_3 due to the loading of ZrO_2. However the resulted MnO_x/ZrO_2-Al_2O_3 catalyst exhibitshigher activity for methane combustion than MnO_x/Al_2O_3, because the addition of ZrO_2 ontoAl_2O_3 is beneficial for the dispersion of Mn species and the improvement of the lattice oxygenactivity in MnO_x, subsequently the activation of methane during combustion. The optimum loading ofZr in MnO_x/ZrO_2-Al_2O_3 is in the range of 5%-10% correlated with the calcination temperatures ofcatalyst supports.展开更多
Rare earth ion-doped Y_(3)Al_(5)O_(12)(YAG)-based transparent ceramics have been used as important laser gain media for a long time,yet the doping concentration of active ions is limited due to concentration quenching...Rare earth ion-doped Y_(3)Al_(5)O_(12)(YAG)-based transparent ceramics have been used as important laser gain media for a long time,yet the doping concentration of active ions is limited due to concentration quenching,wherein the inflexion concentration quenching of Nd^(3+)is recognized as 1.0 at%.In this work,YAG-Al_(2)O_(3) nanocrystalline transparent ceramics with a concentration of Nd^(3+)(O-5.0 at%)were fabricated via amorphous crystallization,and the crystal structure evolution,morphology,and optical properties were systematically investigated by differential scanning calorimetry(DSC),X-ray powder diffraction(XRD),transmission electron microscopy(TEM),magnetic resonation(MAS),nuclear magnetic resonation(NMR),and fluorescence spectroscopy.The doping of Nd^(3+)can promote the transition of Al[5]and Al[6]to Al[14],indicating improvements in the ability of the amorphous material to form Nd^(3+):Y_(2)O_(3)-Al_(2)O_(3) vitrified beads,and 1.5 at%Nd^(3+):YAG-Al_(2)O_(3) nanocrystalline transparent ceramics can be obtained by crystallization at 1050℃ with a matrix composed of YAG and concomitant δ-Al_(2)O_(3) and θ-Al_(2)O_(3).The nanocrystalline transparent ceramics show an internal transmitance of 89.56%at 1064 nm,and the strongest emission peak corresponds to the energy transfer from 4F_(3/2) to 4l_(11/2) of Nd^(3+)with a fluorescence lifetime of 231μs when pumped by an 808 nm laser.Specifically,spectral broadening begins to occur,indicating the onset of concentration quenching,when the concentration of Nd^(3+)exceeds 1.5 at%,substantially higher than the 1.0 at% observed in YAG ceramics.YAG-Al_(2)O_(3) nanocrystalline transparent ceramics obtained by amorphous crystalization can be utilized as the matrix to increase the inflexion point of doping concentration quenching of Nd^(3+),and this material may have great potential as a laser gain medium.展开更多
基金This work was financially supported by Shandong Provincial Department of Science and Technology(project number:981206403)and the State Key Laboratory of Coal Conversion at Institute of Coal Chemistry of CAS(2002-2003)
文摘MnO_x/Al_2O_3 and MnO_x/ZrO_2-Al_2O_3 catalysts were prepared by incipientwetness impregnation of Mn(CH_3COO)_2 on the corresponding supports, followed by thecharacterization using X-ray diffraction (XRD), temperature programmed reduction (TPR) and BETsurface area techniques. The result shows the BET surface area of ZrO_2-Al_2O_3 is lower than thatof Al_2O_3 due to the loading of ZrO_2. However the resulted MnO_x/ZrO_2-Al_2O_3 catalyst exhibitshigher activity for methane combustion than MnO_x/Al_2O_3, because the addition of ZrO_2 ontoAl_2O_3 is beneficial for the dispersion of Mn species and the improvement of the lattice oxygenactivity in MnO_x, subsequently the activation of methane during combustion. The optimum loading ofZr in MnO_x/ZrO_2-Al_2O_3 is in the range of 5%-10% correlated with the calcination temperatures ofcatalyst supports.
基金National Natural Science Foundation of China (52032011)State Key Laboratory of New Ceramic and Fine Processing Tsinghua University (KF 202007)Youth Fund of China Building Materials Academy (ZD-16)。
基金This work was financially supported by the National Natural Science Foundation of China(No.51972018).
文摘Rare earth ion-doped Y_(3)Al_(5)O_(12)(YAG)-based transparent ceramics have been used as important laser gain media for a long time,yet the doping concentration of active ions is limited due to concentration quenching,wherein the inflexion concentration quenching of Nd^(3+)is recognized as 1.0 at%.In this work,YAG-Al_(2)O_(3) nanocrystalline transparent ceramics with a concentration of Nd^(3+)(O-5.0 at%)were fabricated via amorphous crystallization,and the crystal structure evolution,morphology,and optical properties were systematically investigated by differential scanning calorimetry(DSC),X-ray powder diffraction(XRD),transmission electron microscopy(TEM),magnetic resonation(MAS),nuclear magnetic resonation(NMR),and fluorescence spectroscopy.The doping of Nd^(3+)can promote the transition of Al[5]and Al[6]to Al[14],indicating improvements in the ability of the amorphous material to form Nd^(3+):Y_(2)O_(3)-Al_(2)O_(3) vitrified beads,and 1.5 at%Nd^(3+):YAG-Al_(2)O_(3) nanocrystalline transparent ceramics can be obtained by crystallization at 1050℃ with a matrix composed of YAG and concomitant δ-Al_(2)O_(3) and θ-Al_(2)O_(3).The nanocrystalline transparent ceramics show an internal transmitance of 89.56%at 1064 nm,and the strongest emission peak corresponds to the energy transfer from 4F_(3/2) to 4l_(11/2) of Nd^(3+)with a fluorescence lifetime of 231μs when pumped by an 808 nm laser.Specifically,spectral broadening begins to occur,indicating the onset of concentration quenching,when the concentration of Nd^(3+)exceeds 1.5 at%,substantially higher than the 1.0 at% observed in YAG ceramics.YAG-Al_(2)O_(3) nanocrystalline transparent ceramics obtained by amorphous crystalization can be utilized as the matrix to increase the inflexion point of doping concentration quenching of Nd^(3+),and this material may have great potential as a laser gain medium.
