In this study,isobutane dehydrogenation to isobutene reaction was carried out in a series of PtCu bimetallic catalysts prepared by coimpregnation method.The catalysts were characterized by means of several techniques,...In this study,isobutane dehydrogenation to isobutene reaction was carried out in a series of PtCu bimetallic catalysts prepared by coimpregnation method.The catalysts were characterized by means of several techniques,including XRD,N_(2) adsorptiondesorption,TEM,XPS,H2TPR and TG.The results show that the existence of LaAlO_(3) perovskite can enhance the dispersion and sintering resistance of metal nanoparticles and facilitate the transfer of carbon deposits from active sites to the support.Interestingly,the perovskite nanoparticles can also inhibit the reduction of CuOx and the formation of PtCu alloys,resulting in the suitable interaction between Pt and Cu.The PtCu/LaAlO_(3)/SiO_(2)catalyst exhibits the optimal dehydrogenation performance with an isobutane conversion of 47%and isobutene selectivity of 92%after 310 min reaction,which was ascribed to the unique role of LaAlO_(3) perovskite as well as the appropriate PtCu interaction.展开更多
Pure nanocrystalline LaAlO3 powders were synthesized by W/O microemulsion consisting of water, Tween-80 (surfactant), n-Hexyl alcohol (cosurfactant), and cyclohexane (oil). Precursor hydroxides were precipitated in th...Pure nanocrystalline LaAlO3 powders were synthesized by W/O microemulsion consisting of water, Tween-80 (surfactant), n-Hexyl alcohol (cosurfactant), and cyclohexane (oil). Precursor hydroxides were precipitated in the aqueous cores of W/O microemulsions and then separated and calcined to obtain nanocrystalline LaAlO3 powder. The decomposition behavior of the precursors hydroxides were studied by thermogravimetry analysis (TGA). The precursor hydroxides were calcined at different temperatures and the phase evolution was studied by X-ray powder diffraction (XRD). And the morphology of LaAlO3 powder was studied by transmission electron microscopy (TEM). The crystallite size was less than 50 nm and the shape of the particle is approximately spherical.展开更多
LaAlO_(3)/SrTiO_(3)(LAO/STO)heterostructures have shown a strong persistent photoconductivity(PPC)at room temperature.The abnormally strong PPC has attracted immense research interest due to its possible applications ...LaAlO_(3)/SrTiO_(3)(LAO/STO)heterostructures have shown a strong persistent photoconductivity(PPC)at room temperature.The abnormally strong PPC has attracted immense research interest due to its possible applications in optically-tunable electronic devices.Despite its promise,the fundamental understanding of the PPC in the LAO/STO heterostructures is still elusive.Herein,we report that the giant PPC origi-nates from the photo-induced valence change in oxygen vacancies near the LAO/STO interface.Our spec-tral analysis of the photocurrent and the model-fitting study consistently show that the ionized oxygen vacancies near the interface are neutralized during the electron relaxation process.They hinder the complete relaxation of the photoexcited electrons by the deeply-located oxygen vacancies and result in the strong PPC.The change in the ionization state distribution of the oxygen vacancies is probed by the per-sistent noise behavior at the frequency between 1 kHz and 20 kHz regime.These results provide insight into the role of oxygen vacancies in influencing the internal charge distribution and triggering the PPC phenomena in complex oxide heterostructures.展开更多
Coreeshell structured Bi_(0.5)Na_(0.5)TiO_(3)eKTaO_(3)þx%(in mass)Li_(2)CO_(3)ceramics were fabricated in this study.Increasing x from 0 to 2 leads to the decrease of sintering temperature from 1175℃to 1020℃.Th...Coreeshell structured Bi_(0.5)Na_(0.5)TiO_(3)eKTaO_(3)þx%(in mass)Li_(2)CO_(3)ceramics were fabricated in this study.Increasing x from 0 to 2 leads to the decrease of sintering temperature from 1175℃to 1020℃.The limited diffusion of Ta5þresults in chemical heterogeneities and coreeshell microstructures.The Ta5þ-depleted cores show the nanodomains(~10 nm),while the Ta^(5+)-rich shells display the polar nanoregions(1e2 nm).From x¼0 to 1,the appearance of cores with nanodomains contributes to the increase of dielectric constant and maximum polarization,while the further addition of Li2CO3 suppresses the dielectric and polarization responses due to the reduced grain sizes and polarization coupling.The enhanced dielectric relaxation and existence of core-shell microstructure with different polarization levels help to optimize the dielectric temperature stability.The x¼2 ceramics exhibit a stable high dielectric constant~1400 over a wide temperature range of 20e520℃.More encouragingly,the ultrafine grain size and coreeshell microstructure in the x¼2 ceramics greatly benefit the improvement of breakdown strength.Combined with the delayed polarization saturation and high ergodicity,a high recoverable energy density of~5.07 J/cm3 is obtained under 44 kV/mm,with a high efficiency of~85.17%.展开更多
The article describes the approaches for a reliable,quantitative compositional analysis of lead-free perovskite ceramics in powder and bulk forms that contain volatile alkaline compounds.The combination of scanning el...The article describes the approaches for a reliable,quantitative compositional analysis of lead-free perovskite ceramics in powder and bulk forms that contain volatile alkaline compounds.The combination of scanning electron microscopy(SEM)and transmission electron microcopy(TEM)with electron-probe analytical techniques,such as energy-dispersive X-ray spectroscopy(EDS),wavelength-dispersive X-ray spectroscopy(WDS)and electron-energy-loss spectroscopy(EELS)makes it possible to determine the true chemical composition,from precursor powders to synthesized ceramics or single crystals.The microscale(SEM)and nanoscale(TEM)analytical methods also give an insight into the local variations of the chemical composition.展开更多
基金the National Natural Science Foundation of China(21776214)and State Key Laboratory of Chemical Resource Engineering.
文摘In this study,isobutane dehydrogenation to isobutene reaction was carried out in a series of PtCu bimetallic catalysts prepared by coimpregnation method.The catalysts were characterized by means of several techniques,including XRD,N_(2) adsorptiondesorption,TEM,XPS,H2TPR and TG.The results show that the existence of LaAlO_(3) perovskite can enhance the dispersion and sintering resistance of metal nanoparticles and facilitate the transfer of carbon deposits from active sites to the support.Interestingly,the perovskite nanoparticles can also inhibit the reduction of CuOx and the formation of PtCu alloys,resulting in the suitable interaction between Pt and Cu.The PtCu/LaAlO_(3)/SiO_(2)catalyst exhibits the optimal dehydrogenation performance with an isobutane conversion of 47%and isobutene selectivity of 92%after 310 min reaction,which was ascribed to the unique role of LaAlO_(3) perovskite as well as the appropriate PtCu interaction.
基金Natural Science Foundation Project of Chongqing Science and Technology Commission (2005BA4019)
文摘Pure nanocrystalline LaAlO3 powders were synthesized by W/O microemulsion consisting of water, Tween-80 (surfactant), n-Hexyl alcohol (cosurfactant), and cyclohexane (oil). Precursor hydroxides were precipitated in the aqueous cores of W/O microemulsions and then separated and calcined to obtain nanocrystalline LaAlO3 powder. The decomposition behavior of the precursors hydroxides were studied by thermogravimetry analysis (TGA). The precursor hydroxides were calcined at different temperatures and the phase evolution was studied by X-ray powder diffraction (XRD). And the morphology of LaAlO3 powder was studied by transmission electron microscopy (TEM). The crystallite size was less than 50 nm and the shape of the particle is approximately spherical.
基金This work is supported by the National Research Foundation of Korea(NRF)grant funded by the Korea government(MSIT)(Nos.2021R1C1C1011219 and2021R1A4A1032085)K.Eomwould like to acknowledge the support by National Research Founda-tion of Korea through the Basic Science Research Program(NRF-2022R1C1C2010693)J.W.Lee acknowledges the support from Ba-sic Science Research Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Education(No.2022R1I1A1A01068965).
文摘LaAlO_(3)/SrTiO_(3)(LAO/STO)heterostructures have shown a strong persistent photoconductivity(PPC)at room temperature.The abnormally strong PPC has attracted immense research interest due to its possible applications in optically-tunable electronic devices.Despite its promise,the fundamental understanding of the PPC in the LAO/STO heterostructures is still elusive.Herein,we report that the giant PPC origi-nates from the photo-induced valence change in oxygen vacancies near the LAO/STO interface.Our spec-tral analysis of the photocurrent and the model-fitting study consistently show that the ionized oxygen vacancies near the interface are neutralized during the electron relaxation process.They hinder the complete relaxation of the photoexcited electrons by the deeply-located oxygen vacancies and result in the strong PPC.The change in the ionization state distribution of the oxygen vacancies is probed by the per-sistent noise behavior at the frequency between 1 kHz and 20 kHz regime.These results provide insight into the role of oxygen vacancies in influencing the internal charge distribution and triggering the PPC phenomena in complex oxide heterostructures.
基金supports from the National Key R&D Programof China(Grant No.2021YFB2012100)and the Special Funding Support for the Construction of Innovative Provinces in Hunan Province of China(Grant No.2020GK2062).Xuefan Zhou(Postdoc)is particularly grateful for the support from the China National Postdoctoral Program for Innovative Talents(Grant No.BX2021377).
文摘Coreeshell structured Bi_(0.5)Na_(0.5)TiO_(3)eKTaO_(3)þx%(in mass)Li_(2)CO_(3)ceramics were fabricated in this study.Increasing x from 0 to 2 leads to the decrease of sintering temperature from 1175℃to 1020℃.The limited diffusion of Ta5þresults in chemical heterogeneities and coreeshell microstructures.The Ta5þ-depleted cores show the nanodomains(~10 nm),while the Ta^(5+)-rich shells display the polar nanoregions(1e2 nm).From x¼0 to 1,the appearance of cores with nanodomains contributes to the increase of dielectric constant and maximum polarization,while the further addition of Li2CO3 suppresses the dielectric and polarization responses due to the reduced grain sizes and polarization coupling.The enhanced dielectric relaxation and existence of core-shell microstructure with different polarization levels help to optimize the dielectric temperature stability.The x¼2 ceramics exhibit a stable high dielectric constant~1400 over a wide temperature range of 20e520℃.More encouragingly,the ultrafine grain size and coreeshell microstructure in the x¼2 ceramics greatly benefit the improvement of breakdown strength.Combined with the delayed polarization saturation and high ergodicity,a high recoverable energy density of~5.07 J/cm3 is obtained under 44 kV/mm,with a high efficiency of~85.17%.
基金The authors wish to acknowledge the-nancial support of Slovenian Research Agency(P2-105)the Ministry of Higher Education,Science and Technology of Slovenia,the 5 FP project LEAF,the 6FP project IMMEDIATE and the 6FP NoE MIND.
文摘The article describes the approaches for a reliable,quantitative compositional analysis of lead-free perovskite ceramics in powder and bulk forms that contain volatile alkaline compounds.The combination of scanning electron microscopy(SEM)and transmission electron microcopy(TEM)with electron-probe analytical techniques,such as energy-dispersive X-ray spectroscopy(EDS),wavelength-dispersive X-ray spectroscopy(WDS)and electron-energy-loss spectroscopy(EELS)makes it possible to determine the true chemical composition,from precursor powders to synthesized ceramics or single crystals.The microscale(SEM)and nanoscale(TEM)analytical methods also give an insight into the local variations of the chemical composition.
