Au sites supported on Ti-containing materials(Au/Ti-containing catalyst)are currently considered as a promising catalyst for the propylene epoxidation owing to the synergistic effect that hydrogen peroxide species for...Au sites supported on Ti-containing materials(Au/Ti-containing catalyst)are currently considered as a promising catalyst for the propylene epoxidation owing to the synergistic effect that hydrogen peroxide species formed on Au sites diffuses to the Ti sites to form the Ti-hydroperoxo intermedi-ates and contributes to the formation of propylene oxide(PO).In principle,thermal treatment will significantly affect the chemical and physical structures of Ti-containing materials.Consequently,the synergy between tailored Ti sites with different surface properties and Au sites is highly expected to enhance the catalytic performance for the reaction.Herein,we systematically studied the intrinsic effects of different microenvironments around Ti sites on the PO adsorption/desorption and conversion,and then effectively improved the catalytic performance by tailoring the number of surface hydroxyl groups.The Ti^(Ⅵ) material with fewer hydroxyls stimulates a remarkable enhancement in PO selectivity and H_(2) efficiency compared to the Ti^(Ⅵ) material that possessed more hydroxyls,offering a 7-fold and 4-fold increase,respectively.As expected,the Ti^(Ⅵ+Ⅳ) and Ti^(Ⅳ) materials also exhibit a similar phenomenon to the Ti^(Ⅵ) materials through the same thermal treatment,which strongly supports that the Ti sites microenvironment is an important factor in suppressing PO con-version and enhancing catalytic performance.These insights could provide guidance for the rational preparation and optimization of Ti-containing materials synergizing with Au catalysts for propylene epoxidation.展开更多
1.0μm gate-length GaAs-based MHEMTs have been fabricated by MBE epitaxial material and contact-mode lithography technology. Pt/Ti/Pt/Au and Ti/Pt/Au were evaporated to form gate metals. Excellent DC and RF performanc...1.0μm gate-length GaAs-based MHEMTs have been fabricated by MBE epitaxial material and contact-mode lithography technology. Pt/Ti/Pt/Au and Ti/Pt/Au were evaporated to form gate metals. Excellent DC and RF performances have been obtained, and the transconductance, maximum saturation drain current density, threshold voltage, current cut-off frequency,and maximum oscillation frequency of Pt/Ti/Pt/Au and Ti/Pt/Au MHEMTs were 502 （503） mS/mm, 382（530）mA/mm,0.1（ - 0.5）V,13.4（14.8）GHz,and 17.0（17.5）GHz,respectively. DC-10GHz single-pole double-throw （SPDT） switch MMICs have been designed and fabricated by Ti/Pt/Au MHEMTs. Insertion loss,isolation,input,and out- put return losses of SPDT chips were better than 2.93,23.34,and 20dB.展开更多
文摘Au sites supported on Ti-containing materials(Au/Ti-containing catalyst)are currently considered as a promising catalyst for the propylene epoxidation owing to the synergistic effect that hydrogen peroxide species formed on Au sites diffuses to the Ti sites to form the Ti-hydroperoxo intermedi-ates and contributes to the formation of propylene oxide(PO).In principle,thermal treatment will significantly affect the chemical and physical structures of Ti-containing materials.Consequently,the synergy between tailored Ti sites with different surface properties and Au sites is highly expected to enhance the catalytic performance for the reaction.Herein,we systematically studied the intrinsic effects of different microenvironments around Ti sites on the PO adsorption/desorption and conversion,and then effectively improved the catalytic performance by tailoring the number of surface hydroxyl groups.The Ti^(Ⅵ) material with fewer hydroxyls stimulates a remarkable enhancement in PO selectivity and H_(2) efficiency compared to the Ti^(Ⅵ) material that possessed more hydroxyls,offering a 7-fold and 4-fold increase,respectively.As expected,the Ti^(Ⅵ+Ⅳ) and Ti^(Ⅳ) materials also exhibit a similar phenomenon to the Ti^(Ⅵ) materials through the same thermal treatment,which strongly supports that the Ti sites microenvironment is an important factor in suppressing PO con-version and enhancing catalytic performance.These insights could provide guidance for the rational preparation and optimization of Ti-containing materials synergizing with Au catalysts for propylene epoxidation.
文摘1.0μm gate-length GaAs-based MHEMTs have been fabricated by MBE epitaxial material and contact-mode lithography technology. Pt/Ti/Pt/Au and Ti/Pt/Au were evaporated to form gate metals. Excellent DC and RF performances have been obtained, and the transconductance, maximum saturation drain current density, threshold voltage, current cut-off frequency,and maximum oscillation frequency of Pt/Ti/Pt/Au and Ti/Pt/Au MHEMTs were 502 （503） mS/mm, 382（530）mA/mm,0.1（ - 0.5）V,13.4（14.8）GHz,and 17.0（17.5）GHz,respectively. DC-10GHz single-pole double-throw （SPDT） switch MMICs have been designed and fabricated by Ti/Pt/Au MHEMTs. Insertion loss,isolation,input,and out- put return losses of SPDT chips were better than 2.93,23.34,and 20dB.
