Positron lifetimes in polyethylene glycol (PEG) polymer have been measured as a function of polymerization degree N (N = 25 - 500). It is observed that all the positron parameters are strongly dependent on N when N≤2...Positron lifetimes in polyethylene glycol (PEG) polymer have been measured as a function of polymerization degree N (N = 25 - 500). It is observed that all the positron parameters are strongly dependent on N when N≤250, and then tend to constant levels when N≥250. The variations of the longest-lived component (I3,τ3) show that the size of free- volume holes has a minimum at N - 100 and the hole concentration decreases with N. These trends may be due to the variations in crystallinity, the chain ends, entanglements and the Van der Waals interaction between segments. The variations of the second component (I2,τ2) with N reflect the changes of defect properties in crystalline regions of PEG.展开更多
Distribution of metals on Pd-SnO2/D3520 catalysts and state of the catalystswere studied with SEM, XRD. The interactlbn between metals and supped or between Pd and Sn or Ph were studied by IR, XPS. In addition, the re...Distribution of metals on Pd-SnO2/D3520 catalysts and state of the catalystswere studied with SEM, XRD. The interactlbn between metals and supped or between Pd and Sn or Ph were studied by IR, XPS. In addition, the relationship ofthe activity for catalytic hydrogenation of the olefins and outer layer valence electrondensity of Pd was discussed. The results showed that these catalysts had suitablesurface state, the metals were uniformly dispersed on the surface layer of the suppnd. There were not obvious interaction between the metals and the supal. Therewas strong interaction between Pd and Sn (or Ph) in the catalysts. The catalytic activity for hydrogenation was related to outer layer valence electron density of Pd.展开更多
Distribution of metals on Pd - SnO_2/D_(3520) catalysts and state of the catalysts were studied with SEM, XRD. The interaction between metals and support or between Pd and Sn or Ph were studied by IR, XPS. In addition...Distribution of metals on Pd - SnO_2/D_(3520) catalysts and state of the catalysts were studied with SEM, XRD. The interaction between metals and support or between Pd and Sn or Ph were studied by IR, XPS. In addition, the relationship of the activity for catalytic hydrogenation of the olefins and outer layer valence electron density Of Pd was discussed. The results showed that these catalysts had suitable surface state, the metals were uniformly dispersed on the surface layer of the suPPort. There were not obvious lute7uction between the metals and the suPPort. There was strong interaction between Pd and Sn (or Pb) in the catalysts. The catalytic activity for hydrogenation was related to outer layer silence electron density of Pd.展开更多
基金The Project Supported by National Natural Science Foundation of China
文摘Positron lifetimes in polyethylene glycol (PEG) polymer have been measured as a function of polymerization degree N (N = 25 - 500). It is observed that all the positron parameters are strongly dependent on N when N≤250, and then tend to constant levels when N≥250. The variations of the longest-lived component (I3,τ3) show that the size of free- volume holes has a minimum at N - 100 and the hole concentration decreases with N. These trends may be due to the variations in crystallinity, the chain ends, entanglements and the Van der Waals interaction between segments. The variations of the second component (I2,τ2) with N reflect the changes of defect properties in crystalline regions of PEG.
文摘Distribution of metals on Pd-SnO2/D3520 catalysts and state of the catalystswere studied with SEM, XRD. The interactlbn between metals and supped or between Pd and Sn or Ph were studied by IR, XPS. In addition, the relationship ofthe activity for catalytic hydrogenation of the olefins and outer layer valence electrondensity of Pd was discussed. The results showed that these catalysts had suitablesurface state, the metals were uniformly dispersed on the surface layer of the suppnd. There were not obvious interaction between the metals and the supal. Therewas strong interaction between Pd and Sn (or Ph) in the catalysts. The catalytic activity for hydrogenation was related to outer layer valence electron density of Pd.
文摘Distribution of metals on Pd - SnO_2/D_(3520) catalysts and state of the catalysts were studied with SEM, XRD. The interaction between metals and support or between Pd and Sn or Ph were studied by IR, XPS. In addition, the relationship of the activity for catalytic hydrogenation of the olefins and outer layer valence electron density Of Pd was discussed. The results showed that these catalysts had suitable surface state, the metals were uniformly dispersed on the surface layer of the suPPort. There were not obvious lute7uction between the metals and the suPPort. There was strong interaction between Pd and Sn (or Pb) in the catalysts. The catalytic activity for hydrogenation was related to outer layer silence electron density of Pd.
