An accelerator storage ring needs clean ultrahigh vacuum.A TiZrV non-evaporable getter(NEG) film deposited on interior walls of the chamber can realize distributed pumping,effective vacuum improvement and reduced long...An accelerator storage ring needs clean ultrahigh vacuum.A TiZrV non-evaporable getter(NEG) film deposited on interior walls of the chamber can realize distributed pumping,effective vacuum improvement and reduced longitudinal pressure gradient.But accumulation of pollutants such as N_2 and O_2 will decrease the adsorption ability of the NEG,leading to a reduction of NEG lifetime.Therefore,an NEG thin film coated with a layer of Pd,which has high diffusion rate and absorption ability for H_2,can extend the service life of NEG and improve the pumping rate of H_2 as well.In this paper,with argon as discharge gas,a magnetron sputtering method is adopted to prepare TiZrV-Pd films in a long straight pipe.By SEM measurement,deposition rates of TiZrV-Pd films are analyzed under different deposition parameters,such as magnetic field strength,gas flow rate,discharge current,discharge voltage and working pressure.By comparing the experimental results with the simulation results based on Sigmund's theory,the Pd deposition rate C can be estimated by the sputtered depth.展开更多
A series of oxygen deficient perovskite supported palladium catalysts were prepared by the “solid phase crystallization'(spc) method and investigated with XRD, TPR, TPD, TEM, XPS, BET analysis and CO oxidation. I...A series of oxygen deficient perovskite supported palladium catalysts were prepared by the “solid phase crystallization'(spc) method and investigated with XRD, TPR, TPD, TEM, XPS, BET analysis and CO oxidation. It was found that Pd/perovskite catalysts synthesized by the spc method were more active for CO oxidation than the calcined LaCo 0 95 Pd 0 05 O 3, where Pd dispersed in the solid solution. H 2 reducing treatment in the spc method could yield not only high dispersed fine Pd particles on the perovskite surface but also oxygen deficient structure. In these perovskite supported Pd catalysts, oxygen vacancies adsorbed, activated and supplied oxygen to the active Pd sites, where the oxidation occurred with adsorbed CO. The high activities were due to the cooperative action of Pd and oxygen vacancies.展开更多
Many attempts have been made to control the regioselectivity for olefin poly- merization by varying the structures of ligands in catalysts. The regioselectivity of propylene polymerization was investigated by replacin...Many attempts have been made to control the regioselectivity for olefin poly- merization by varying the structures of ligands in catalysts. The regioselectivity of propylene polymerization was investigated by replacing a nitrogen atom in the Pd(II) diimine catalyst with an oxygen atom from density functional theory method at the B3LYP/LANL2DZ level. The results show that the 1,2-insertion becomes a rival mechanism to the 2,1-insertion when the nitrogen atom is replaced by the oxygen atom leading to an asymmetric environment in the catalyst, and that the steric effect in the asymmetrical catalyst plays an important part in the polymerization. The insertion barrier from 2-O is much higher than that from 2-N. A pyramid transition state was characterized for the catalyst to convert 2-O back to 2-N through internal rotation. The propylene prefers to coordinate at the opposite side of O in the catalyst. This is the driving force for the internal rotation. The results are significant for isotactic and syndiotactic polymerization.展开更多
基金supported by the National Natural Science Funds of China(No.11205155)Fundamental Research Funds for the Central Universities(WK2310000041)
文摘An accelerator storage ring needs clean ultrahigh vacuum.A TiZrV non-evaporable getter(NEG) film deposited on interior walls of the chamber can realize distributed pumping,effective vacuum improvement and reduced longitudinal pressure gradient.But accumulation of pollutants such as N_2 and O_2 will decrease the adsorption ability of the NEG,leading to a reduction of NEG lifetime.Therefore,an NEG thin film coated with a layer of Pd,which has high diffusion rate and absorption ability for H_2,can extend the service life of NEG and improve the pumping rate of H_2 as well.In this paper,with argon as discharge gas,a magnetron sputtering method is adopted to prepare TiZrV-Pd films in a long straight pipe.By SEM measurement,deposition rates of TiZrV-Pd films are analyzed under different deposition parameters,such as magnetic field strength,gas flow rate,discharge current,discharge voltage and working pressure.By comparing the experimental results with the simulation results based on Sigmund's theory,the Pd deposition rate C can be estimated by the sputtered depth.
文摘A series of oxygen deficient perovskite supported palladium catalysts were prepared by the “solid phase crystallization'(spc) method and investigated with XRD, TPR, TPD, TEM, XPS, BET analysis and CO oxidation. It was found that Pd/perovskite catalysts synthesized by the spc method were more active for CO oxidation than the calcined LaCo 0 95 Pd 0 05 O 3, where Pd dispersed in the solid solution. H 2 reducing treatment in the spc method could yield not only high dispersed fine Pd particles on the perovskite surface but also oxygen deficient structure. In these perovskite supported Pd catalysts, oxygen vacancies adsorbed, activated and supplied oxygen to the active Pd sites, where the oxidation occurred with adsorbed CO. The high activities were due to the cooperative action of Pd and oxygen vacancies.
基金This work was supported by the Natural Science Foundation of Heilongjiang Province (No. B0313) and Research Foundation of China University of Mining and Technology
文摘Many attempts have been made to control the regioselectivity for olefin poly- merization by varying the structures of ligands in catalysts. The regioselectivity of propylene polymerization was investigated by replacing a nitrogen atom in the Pd(II) diimine catalyst with an oxygen atom from density functional theory method at the B3LYP/LANL2DZ level. The results show that the 1,2-insertion becomes a rival mechanism to the 2,1-insertion when the nitrogen atom is replaced by the oxygen atom leading to an asymmetric environment in the catalyst, and that the steric effect in the asymmetrical catalyst plays an important part in the polymerization. The insertion barrier from 2-O is much higher than that from 2-N. A pyramid transition state was characterized for the catalyst to convert 2-O back to 2-N through internal rotation. The propylene prefers to coordinate at the opposite side of O in the catalyst. This is the driving force for the internal rotation. The results are significant for isotactic and syndiotactic polymerization.
