The promoting effect of La2O3 on Ni/γ-Al2O3 methanation catalyst was investigated by XPS, TPR and TPD methods. Results indicated that La2O3 can be partially reduced to LaOx (x＜3/2) during H2 reduction of the Ni cata...The promoting effect of La2O3 on Ni/γ-Al2O3 methanation catalyst was investigated by XPS, TPR and TPD methods. Results indicated that La2O3 can be partially reduced to LaOx (x＜3/2) during H2 reduction of the Ni catalysts with La2O3.The excess charge associated with the LaOx can be transfered to Ni. It weakened C-O bond strength, accelerated CO dissociation, proportionation and methanation reaction.The interaction between NiO and Al2O3 can be suppressed and the formation of NiAl2O4-like species can be reduced by adding La2O3. With the increase of La2O3 con tents the fraction of NiO which is easier to be reduced becomes larger.The fact that there was more residual H2 on the catalyst with La2O3 means that it is able to retain some H2. Besides, the distribution of CO adsorption sites of the Ni catalyst was shifted by adding La2O3.展开更多
The effects of rare-earth La_2O_3 addition on microstructures and electrical properties of SrTiO_3 ceramics were investigated. Semiconductor SrTiO_3-based voltage-sensing and dielectric dual functional ceramics was pr...The effects of rare-earth La_2O_3 addition on microstructures and electrical properties of SrTiO_3 ceramics were investigated. Semiconductor SrTiO_3-based voltage-sensing and dielectric dual functional ceramics was prepared by a single step sintering technology in this study, and the effects of the content of La_2O_3 on characteristics of the product were discussed in terms of microstructures and electrical properties of materials. The results show that SrTiO_3-based ceramics doped with La_2O_3 exhibits more homogeneous grain distribution, greater grain size, and excellent voltage sensing and dielectric characteristics than those without La_2O_3 doping. The samples doped with 1 1% La_2O_3 were sintered at 1420 ℃ in N_2+C weak reducing atmosphere. The average grain size of the samples doped with La_2O_3 is 40 μm, the breakdown voltage of 19.7 V·mm^(-1), the nonlinear exponent of 7.2, and dielectric constant of 22500. The results reveal that final products are suitable to use in low operating voltage.展开更多
The recrystallization behavior of Mo wires doped with various contents of La2O3,which were prepared by powder metallurgy method,was investigated using TEM and SEM in detail.It is shown that the recrystallization tempe...The recrystallization behavior of Mo wires doped with various contents of La2O3,which were prepared by powder metallurgy method,was investigated using TEM and SEM in detail.It is shown that the recrystallization temperature and recrystallized microstructure of Mo-La2O3 wires are strongly dependent on the La2O3 contents.An interlocked large grain structure is formed in Mo-La2O3 wires with contents of 0.2-0.4 wt% La2O3,on the other hand,Mo─La2O3 wires containing less than 0.1 or more than 0.8 wt% La2O3 show equiaxed grain structure.The reason for this is the difference between the longitudinal interparticle spacing and the transverse spacing of La2O3 particles in various Mo-La2O3 wires,which was observed by using TEM.展开更多
文摘The promoting effect of La2O3 on Ni/γ-Al2O3 methanation catalyst was investigated by XPS, TPR and TPD methods. Results indicated that La2O3 can be partially reduced to LaOx (x＜3/2) during H2 reduction of the Ni catalysts with La2O3.The excess charge associated with the LaOx can be transfered to Ni. It weakened C-O bond strength, accelerated CO dissociation, proportionation and methanation reaction.The interaction between NiO and Al2O3 can be suppressed and the formation of NiAl2O4-like species can be reduced by adding La2O3. With the increase of La2O3 con tents the fraction of NiO which is easier to be reduced becomes larger.The fact that there was more residual H2 on the catalyst with La2O3 means that it is able to retain some H2. Besides, the distribution of CO adsorption sites of the Ni catalyst was shifted by adding La2O3.
基金Project supported by Science and Technology Foundation of Yunnan Province (2002GG-09)
文摘The effects of rare-earth La_2O_3 addition on microstructures and electrical properties of SrTiO_3 ceramics were investigated. Semiconductor SrTiO_3-based voltage-sensing and dielectric dual functional ceramics was prepared by a single step sintering technology in this study, and the effects of the content of La_2O_3 on characteristics of the product were discussed in terms of microstructures and electrical properties of materials. The results show that SrTiO_3-based ceramics doped with La_2O_3 exhibits more homogeneous grain distribution, greater grain size, and excellent voltage sensing and dielectric characteristics than those without La_2O_3 doping. The samples doped with 1 1% La_2O_3 were sintered at 1420 ℃ in N_2+C weak reducing atmosphere. The average grain size of the samples doped with La_2O_3 is 40 μm, the breakdown voltage of 19.7 V·mm^(-1), the nonlinear exponent of 7.2, and dielectric constant of 22500. The results reveal that final products are suitable to use in low operating voltage.
文摘The recrystallization behavior of Mo wires doped with various contents of La2O3,which were prepared by powder metallurgy method,was investigated using TEM and SEM in detail.It is shown that the recrystallization temperature and recrystallized microstructure of Mo-La2O3 wires are strongly dependent on the La2O3 contents.An interlocked large grain structure is formed in Mo-La2O3 wires with contents of 0.2-0.4 wt% La2O3,on the other hand,Mo─La2O3 wires containing less than 0.1 or more than 0.8 wt% La2O3 show equiaxed grain structure.The reason for this is the difference between the longitudinal interparticle spacing and the transverse spacing of La2O3 particles in various Mo-La2O3 wires,which was observed by using TEM.
