When ethylene-vinyl acetate copolymer, EVA, is heated, a two-stage thermal degradation occurs following its melting. The vinyl
acetate content of the copolymer was determined to be 43.8% by using TA 2950 and TA 2050 thermogravimetric instruments. TG/FTIR
was used to detect the evolved gas. Acetic acid and trans-1-R-4-R'-cyclohexane were the main products evolved from EVA in
the first and second stage, respectively. The apparent activation energies were determined for both stages by differential
Authors:D. Shen, X. Fan, X. Su, J. Zeng, and Y. Dong
The sorption behavior of technetium on pyrrhotine was studied with batch experiments and diluted sulfuric acid (less than 2.88 mol/l) was used to dissolve the technetium adsorbed on pyrrhotine. A significant sorption of technetium on pyrrhotine was observed under aerobic and anaerobic conditions, and the sorption on the mineral was supposed to be due to the reduction of TcO4- to insoluble TcO2.nH2O. Sorbed technetium on the mineral could be desorbed by diluted sulfuric acid. The maximum desorption ratio under aerobic conditions was much higher than that of under anaerobic conditions, meanwhile, the desorption rates under anaerobic conditions were higher than that of under aerobic conditions in the initial stage of the experiments.
Authors:G. Shen, S. Tan, Q. Yang, X. Y. Sun, X. W. Sun, and X. Wang
The hypothesis of niche differentiation with respect to resources is considered to be one of the most influential explanations for the maintenance of species diversity. The hypothesis has been examined extensively by testing its prediction of species-habitat association, which posits that the spatial distribution of species is highly correlated with environmental variables. However, we argue that widespread evidence of the species-habitat association lacks adequate rigor to justify the niche differentiation hypothesis. In this study, we tested whether and to what extent the observed species-habitat association could be caused by ecological processes other than niche differentiation, in a 20-ha subtropical forest plot. The niche differentiation hypothesis was evaluated by testing the species-habitat association and performing a cross-evaluation of the habitat-diversity expectation, which posits that a strong positive correlation exists between species diversity and habitat complexity. Failure to support the habitat-diversity expectation would at a minimum indicate that the niche differentiation hypothesis might not be the main underlying process of species distribution, despite prevalence of the species-habitat association in the same plot. Our analysis revealed that distributions of most species (86.11%) in the plot were significantly associated with at least one of eight topographical and soil nutrient variables. However, there was almost no significant positive correlation between species diversity and habitat complexity at various spatial scales in the same plot. The results indicate that additional caution is warranted when interpreting the species-habitat association from the niche differentiation perspective. A significant species-habitat association indicates only a species’ habitat preference. The association may reveal nothing about interspecific differences in habitat preference, which is a requirement of the niche differentiation hypothesis.
N,N,N',N'-Tetrabutyladipicamide (TBAA) was used for the extraction of nitric acid and uranyl(II) ion from nitric acid media
into toluene. The effects of nitric acid, uranyl(II) ion, and extractant concentration, temperature and back extraction on
the distribution coefficient of uranyl(II) ion have been studied. The main adduct of TBAA and HNO3 is TBAA·HNO3 in 1.0 mol/l nitric acid solution. The 1:2:2 complex of uranyl(II) ion, nitrate ion and TBAA as extracted species is further
confirmed by IR spectra of the extraction of uranyl(II) ion with TBAA. The values of the thermodynamic parameters have also
Authors:X. Chen, W. Feng, W. Miao, Y. Shen, and Y. Yu
Power-time curves and metabolic properties of Tetrahymena thermophila BF5 exposed to different Yb3+ levels were studied by ampoule method of isothermal calorimetry at 28°C. Metabolic rate (r) decreased significantly while peak time (PT) increased with the increase of Yb3+. These results were mainly due to the inhibition of cell growth, which corresponded to the decrease of cell number obtained
by cell counting. Compared with cell counting, calorimetry was sensible, easy to use and convenient for monitoring the toxic
effects of Yb3+ on cells and freshwater ecosystem. It was also found that cell membrane fluidity decreased significantly under the effects
of Yb3+, which indicated that Yb3+ could be membrane active molecules with its effect on cell membranes as fundamental aspect of
Authors:L. Li, X. Wang, J. Shen, L. Zhou, and T. Zhang
Adsorption microcalorimetry has been employed to study the interaction of ethylene with the reduced and oxidized Pt-Ag/SiO2catalysts with different Ag contents to elucidate the modified effect of Ag towards the hydrocarbon processing on platinum
catalysts. In addition, microcalorimetric adsorption of H2, O2, CO and FTIR of CO adsorption were conducted to investigate the influence of Ag on the surface structure of Pt catalyst.
It is found from the microcalorimetric results of H2and O2adsorption that the addition of Ag to Pt/SiO2leads to the enrichment of Ag on the catalyst surface which decreases the size of Pt surface ensembles of Pt-Ag/SiO2catalysts. The microcalorimetry and FTIR of CO adsorption indicates that there still exist sites for linear and bridged CO
adsorption on the surface of platinum catalysts simultaneously although Ag was incorporated into Pt/SiO2. The ethylene microcalorimetric results show that the decrease of ensemble size of Pt surface sites suppresses the formation
of dissociative species (ethylidyne) upon the chemisorption of C2H4on Pt-Ag/SiO2. The differential heat vs. uptake plots for C2H4adsorption on the oxygen-preadsorbed Pt/SiO2and Pt-Ag/SiO2catalysts suggest that the incorporation of Ag to Pt/SiO2could decrease the ability for the oxidation of C2H4.
Carburization and coke deposition of unsupported and carbon-supported Fe, Mo and Fe−Mo catalysts in syngas have been studied
using thermogravimetry. Compositions of the carbides formed are evaluated on the basis of the amount of metals in the catalysts
and amount of carbon deposited during carburization. It is shown that carburization temperature and the nature of the carbides
formed (Fe5C2 and Fe2C for iron and Mo2C for molybdenum) depend on the metals but are influenced by the support and metal loading. Coke deposition on these catalysts
takes place as soon as carburization is complete.
The catalytic performance of unsupported and carbon-supported Fe, Mo and Fe−Mo catalysts for Fischer-Tropsch synthesis is
greatly influenced by the final reduction states of the catalysts. In this investigation, the reduction process of the catalysts
by H2 was studied by using TG-DTG. The reduction process depends not only on the reducibility of metals but also on the nature
of the support. Methanation of the support occurred as soon as the supported metals were completely reduced for the carbon-supported
catalysts. For these, the reduction temperature should by carefully selected so that the metal oxides are reduced as completely
as possible, whilst the methanation of the support must be avoided to obtain optimum reduced catalysts.
Authors:X. Cai, H. Shen, C. Zhang, Y. Wang, and Z. Kong
A simple operation mode to determine the apparent activation energy Ea is introduced. Ea can be determined with a double-curve method by using a constant reaction rate (CRR) approach of Hi-Res TG. The most appropriate
mechanism function f(α) and frequency factor A are determined by a single-curve method when the activation energies provided by the two methods are in good agreement with
each other. The deacetylation of EVA copolymer has been used for illustration. Advantages of the CRR are discussed.
Authors:J. Liu, H. Xu, W. Shen, X. Pan, and Y. Xiang
Mn2O3/-Al2O3 catalysts were prepared by the impregnation method, and the maximum monolayer dispersion capacity or dispersion threshold value of Mn2O3 on the surface of -Al2O3 was determined to be 13.08% from the decomposition mass loss of supported Mn(NO3)2 in the monolayer state. This was compared with the values estimated from a close-packed monolayer model and an interaction model. It was confirmed that the high activities and selectivities of the catalysts for benzoic acid hydrogenation to benzaldehyde are due to the monolayer dispersion of the Mn2O3 on the surface of -Al2O3.