载体焙烧气氛对环氧乙烷银催化剂性能的影响

在不同组成的焙烧气氛中制备了氧化铝载体,对其进行XRD、压汞和SEM表征。将载体浸渍在银氨络合溶液中制得银催化剂,对制备的催化剂进行CO脉冲吸附和O₂-TPD表征,并采用固定床反应器对比评价了反应性能。结果表明,空气混合氮气气氛下焙烧的载体,孔径呈多级分布,氧化铝微观形貌呈“块”状。氮气比例的提升,有利于Ag颗粒的分散和提高催化剂表面低温脱附氧的比例。以70%空气+30%氮气气氛所焙烧载体制备的催化剂相比传统空气焙烧气氛,反应温度降低1.7 ℃,选择性提高1.6%,但更高的氮气比例会造成催化剂的性能劣化。     

Hydrothermal synthesis of Litchi-like SrTiO3 with the help of ethylene glycol

Templated by TiO₂ microspheres , litchi-like SrTiO₃ crystals with a narrow size distribution and monodispersity were synthesized through the combination of regulating the ethylene glycol concentration during the hydrothermal process and the post heat treatment. The results show that when the volume ratio of water and ethylene glycol reached 10:70, microsized SrCO₃ was firstly formed under the hydrothermal process, and then the litchi-like SrTiO₃ powder was obtained after the postheat treatment at 700°C for 4 hours, which shows a large specific surface area of 37.41 m²/g. It is found that the concentration of ethylene glycol aqueous solution plays an important role on the morphology of the SrTiO₃ crystals, and the slightly higher viscosity and proper amount of OH hydroxyl groups facilitate the formation of the micrometer spherical hierarchical surface.     

Influence of Microstructure Modulation of Er~（3＋）-Doped Al_2O_3 on the Photoluminescence Performance

采用溶胶–凝胶法分别制备了掺不同摩尔分数Er3＋的Er3＋：Al2O3粉末和不同摩尔分数Y3＋的0.5%Er3＋：Al2O3（Y3＋：0.5%Er3＋：Al2O3）粉末。利用Y3＋与Al3＋的半径差异,通过共掺不同掺量的Y3＋来调制Al2O3的微结构,用X射线衍射和透射电子显微镜分析样品的结构特征,并通过光致发光光谱研究样品的光致发光特性。结果表明：不同Y3＋和Er3＋共掺杂的Y3＋：Er3＋：Al2O3样品均以-Al2O3为主相;随着Y3＋掺量的增加,Al2O3的晶格缺陷逐渐增多;样品的荧光强度、发射谱宽度及荧光寿命也都随着Y3＋掺量增大而增大。通过Y3＋掺量调制Er3＋所处微结构环境的方法有效地改善了Er3＋：Al2O3材料的发光特性。     

Oxidation of Cl-modified Ag(111) under UHV conditions and ethylene adsorption on the oxidized surface

Oxidation of Cl-modified Ag(111) under UHV conditions was investigated using AES, ISS and HREELS. The results showed that Cl-modified Ag(111) can be easily oxidized at 550 K by 1 × 10^–6 mbar oxygen which was also heated to 550 K. With HREELS two fundamental vibrations at 600 and 1000 cm^–1 were detected for silver oxide and the multiple losses and combination excitations as well. Ethylene adsorption on the oxide was analyzed by HREELS. Surface hydroxyl species was formed at 230 K and stable to above 300 K, which is attributed to silver oxide. Ethylidyne was suggested to form concurrently with hydroxyl species.     

Influence of the type and the comonomer contents on the mechanical behavior of ethylene/α‐olefin copolymers

The influences of the type and concentration of α‐olefin (1‐hexene, 1‐octene, 1‐decene, 1‐octadecene, 4‐methyl‐1‐pentene) on the mechanical behavior and crystallinity degree of some ethylene/α‐olefin copolymers obtained by metallocene catalysts were studied by means of stress/strain experiments. The crystallinity degree of these copolymers has been determined by X‐ray measurements. It has been observed that the copolymers show less resistance to strain as the comonomer content increases and the crystallinity decreases. Most of the studied copolymers exhibit a significant increase in the crystallinity level after the stress/strain experiments. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1194–1200, 1999     

Comparison of the effect of ethylene oxide and γ-irradiation on selected tyrosine-derived polycarbonates and poly(L-lactic acid)

Tyrosine-derived polycarbonates are a new class of degradable polymers that have possible biomedical applications. In this study, the effect of the two most common sterilization techniques, ethylene oxide and γ-irradiation (0.3, 1.1, 3.9, 6.4, 10.6 Mrad), was evaluated for a family of four structurally related tyrosine-derived polycarbonates and for poly(L-lactic acid) (PLLA). The four polycarbonates were poly(DTE carbonate), poly(DTB carbonate), poly(DTH carbonate), and poly(DTO carbonate) and differed only in the length of the pendent chain. Ethylene oxide exposure had little effect on molecular weight, surface composition, mechanical properties, or degradation rate of all test polymers except for poly(DTO carbonate). Poly(DTO carbonate) was unique since following ethylene oxide exposure it degraded faster than did the nonsterilized control. γ-Irradiated tyrosine-derived polycarbonates retained over 81% of their initial molecular weight when exposed to a clinically relevant dose of 3.9 Mrad and retained still 58% of the initial molecular weight when exposed to the highest test dose of 10.6 Mrad. No changes in surface composition and only slight changes in yield strength and the Young's modulus were detected for any of the tyrosine-derived polycarbonates following γ-irradiation. In vitro, irradiated films of poly(DTE carbonate), poly(DTB carbonate), and poly(DTH carbonate) degraded at approximately the same rate as did the nonsterilized films regardless of irradiation dose. Only poly(DTO carbonate), irradiated at high doses, degraded faster than did the control. Medical-grade PLLA was tested under identical conditions. Ethylene oxide exposure of PLLA did not affect the molecular weight, surface composition, mechanical properties, or in vitro degradation rate. However, upon irradiation at 10.6 Mrad, PLLA retained only 29% of its initial molecular weight; a dose of 3.9 Mrad resulted in retention of 49% of the initial molecular weight. In correspondence with earlier publications, irradiation of PLLA induced significant losses in the Young's modulus, % strain at break, and changes in the postirradiation rate of degradation in some specimens. Compared to PLLA, tyrosine-derived polycarbonates are significantly more stable to γ-irradiation and can be sterilized by conventional γ-sterilization techniques. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1499–1510, 1997     

Influence of the longest ethylene and isotactic propylene sequences on crystallization elution fractionation of ethylene/propylene copolymers

Crystallization elution fractionation (CEF) is the newest crystallization-based technique for estimating the chemical composition distribution of ethylene/1-olefin copolymers. Understanding the separation mechanism of CEF for ethylene/propylene copolymers over their full compositional range is challenging because the crystallizabilities of the copolymer chains depend on the longest ethylene sequence and on longest isotactic propylene sequence. We developed a mathematical model to describe the CEF mechanism for ethylene/propylene copolymers over the entire compositional range using population balances for the crystallization and dissolution stages. The joint distribution of longest ethylene and isotactic propylene sequences determines how the copolymer populations crystallize and dissolve. The model was validated with experimental CEF profiles of ethylene/propylene copolymers varying from pure ethylene to propylene homopolymers.     

Influence of multi-step annealing on nanostructure and surface morphology of Y2O3:SiO2 powder

Y₂O₃:SiO₂ powder was synthesized by a sol–gel method, using hydrous yttrium nitrate and hydrous silicon oxide as precursors and HCl as a catalyst. The dried samples were submitted to multi-step annealing schedule in air without applying pressure. A simple four-step annealing schedule with a final stage of about 900 °C for 6.0 h was followed. The samples of Y₂O₃:SiO₂ nanocomposites were obtained with well defined size and shape. Structural changes of the nanocomposites were investigated by XRD, FTIR and TEM. Multi-step annealing scheme with different ramp rates and incubation times allows recovery-relaxation processes within the boundaries and leading to a concomitant linear increase of crystallite size and densification. Almost fully dense quasi-spherical cubic-yttria nanopowder has been demonstrated with an average grain size distribution of 10–40 nm; can be uniformly dispersed in silica matrix.     

Influence of particle size and shape on the rate of hydrogen produced by Al-doped SrTiO3 photocatalysts

Photocatalytic hydrogen production rates have been measured from Al-doped SrTiO₃ with a range of controlled shapes and sizes using a high-throughput parallelized and automated photochemical reactor. It is found that the photocatalytic reactivity is influenced by crystal shape and that crystals with a {1 1 0} to {1 0 0} surface area ratio between 1.3 and 1.8 yield more H₂ than crystals with other ratios. Crystals with a {1 1 0}/{1 0 0} surface area ratio of 1.8 generate hydrogen at 550 μmol h⁻¹ g⁻¹ at pH 7, whereas crystals with only {1 0 0} facets exposed generate hydrogen at 300 μmol h⁻¹ g⁻¹ under the same condition. It is likely that the surface area ratio provides the appropriate balance between the photoanodic reaction on the {1 1 0} surface and the photocathodic reaction on the {1 0 0} surface. In the size range of 250–450 nm, larger crystals produce hydrogen at a rate of 400 μmol h⁻¹ g⁻¹ at pH 7, whereas smaller crystals only produce 200 μmol h⁻¹ g⁻¹, suggesting that the larger crystals reduce the rate of electron–hole recombination or back reaction and that the widths of the space charges within the crystal are comparable to the particle radius.     

不同制备条件对SBA-15介孔氧化硅的形貌、比表面积和孔径分布的影响

研究了表面活性剂用量、水解过程中维持搅拌或静置、水热或微波辐射陈化等反应条件或因素对合成SBA-15的形貌、比表面积以及孔径大小和分布的影响及规律。结果表明,在P123中增加CTAB表面活性剂的用量,所得SBA-15形貌由棒状逐渐转变为球型颗粒;硅源水解过程中,搅拌会使产物倾向于呈现棒状颗粒,而静置水解则有利于成球颗粒的形成。与水热陈化处理相比,微波能快速方便地合成形貌规则、比表面积大且孔径较均一的SBA-15。     

Studies on probing SiO2 surface using BF3 as probe and SiO2/Al2Et3Cl3/TiCl4(PhMgCl) catalytic system for copolymerization of ethylene and propylene

Using BF₃ as probe, the surface of SiO₂ was probed. The effects of the roast temperature on the SiO₂ surface were investigated and a possible mechanism is suggested. Using SiO₂ as starting material for supports, new supported catalysts for copolymerization of ethylene and propylene were prepared and their possible structures are discussed. It was found that higher polymerization productivity, for instance, 480 kg P/mol_Ti h, can be obtained by using a SiO₂/Al₂Et₃Cl₃/TiCl₄ catalytic system and addition of PhMgCl to this catalytic system can significantly increase polymerization activity. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1583–1589, 2000     

Effects of oxidation and redox-properties on the selectivity of heat-treated Ag/Al2O3 catalysts for HC-SCR of NOx

Ag/Al₂O₃ catalysts (2 wt% Ag) have been prepared and calcined at different temperatures to render catalysts with different silver particle size or silver configuration. The differences in activity and selectivity of these catalysts are related to the activity for oxidation of NO and hydrocarbons, the NO_x storage properties, and to the oxidation state of silver.     

纤维素/聚乙二醇共混物中组分比例的变化对共混物Tg的影响规律及模型

应用DSC方法和经典的高分子共混物经验方程估算了纤维素/聚乙二醇共混物的玻璃化转变温度(Tg),并研究了Tg与两组分比例之间的关系。结果显示:该共混物的Tg随纤维素比例增加而降低,且明显低于两个独立组分的Tg,其规律为:Tg=A-B×Ln(WCell/WPEG)。与文献介绍的一些经典的高分子共混物Tg估算公式,如:Fox方程、Gordon-Taylor方程和Kwei方程相比较发现,其中惟有Fox方程似乎比较接近DSC实验导出的模型。     

Effect of poly(ethylene glycol) additives on the photocatalytic activity of TiO2 films prepared by sol–gel processing and low temperature treatments

Photocatalytic activity of titania with poly(ethylene glycol) (PEG) in the sample films made under different operating conditions was investigated by kinetic analysis of photodegradation tests. The sample films, composed of PEG and nano-TiO₂ particles, were prepared by sol–gel processing and then treated thermally under an atmosphere of wet and dry air at different temperatures. After the thermal treatment, photocatalytic activities of the films were evaluated by a UV-exposure test. Results showed that the photoactivity was enhanced by processing in an atmosphere of wet air at 100 °C. Moreover, the presence of poly(ethylene glycol), and the change in surface morphology in the sample films were verified to be the most influential and significant factors to affect the photoactivitic activity.     

Influence of Er3+ substitution on the structural,magnetic, and magnetostrictive properties of cobalt ferrite synthesized from spent Li-ion batteries

This study presents the effect of Er³⁺ substitution for Fe³⁺ at low concentrations on the structural, magnetic, and magnetostrictive properties of cobalt ferrite synthesized by sol–gel method using spent Li-ion batteries as raw materials. The XRD results confirm the formation of pure-phase cubic spinel structure with average crystallite sizes of 24.8–41.5?nm as obtained through the Scherrer formula. Although Er³⁺ substitution does not show any observable changes in morphology, the magnetic and magnetostrictive properties are strongly affected. Density measurements obtained by the Archimedes method reveal that the bulk density decreases and the porosity increases with Er³⁺ substitution because of the formation of intragranular pores during sintering. The saturation magnetization and coercivity of the samples obtained with a vibrating sample magnetometer are influenced by the incorporation of Er³⁺ at the B-sites. Magnetostriction and strain derivative curves show that Er³⁺ substitution makes cobalt ferrite more suitable for advanced magnetomechanical stress sensors and energy-efficient actuator devices.     

Influence of nonionic emulsifiers on the properties of vinyl acetate/VeoVa10 and vinyl acetate/ethylene emulsions and paints

This paper presents results on the influence of the nonionic surfactant on the properties of vinyl acetate/VeoVa10^® and vinyl acetate/ethylene emulsions and paints made thereof. Emulsions were prepared in which the concentration of the nonionic surfactant and its degree of ethoxylation were varied. An increase of the nonionic emulsifier concentration and of the length of the ethylene oxide chain leads to dispersions with smaller particles and higher viscosities. Using these emulsions as binders in high pigmented paints, it was observed that the pigment binding capacity of the interior paints goes through a maximum which is located at a emulsifier concentration of about 2–3% and at a degree of ethoxylation of 17–28 mol ethylene oxide (EO). In (semi-) gloss paints, the gloss of the paint films improves with an increase of the emulsifier concentration and reaches a constant value at around 4% or a degree of ethoxylation of ca. 17 EO-moieties per molecule. The blocking of the films shows a drastic increase at a concentration above 4% and at a chain length of greater than 17 EO-moieties.