Solubility of 1‐hexene in LLDPE synthesized by (2‐MeInd)2ZrCl2/MAO and by Mg(OEt)2/DIBP/TiCl4–TEA

The solubility of 1‐hexene was measured for linear low‐density polyethylenes (LLDPEs) produced over a heterogeneous Ziegler–Natta catalyst, Mg(OEt)₂/DIBP/TiCl₄–TEA (ZN), and over a homogeneous metallocene catalyst, (2‐MeInd)_zZrCl₂–MAO (MT). The 1‐hexene solubility in LLDPEs was well represented by the Flory–Huggins equation with a constant value of χ. ZN–LLDPEs dissolved a larger amount of 1‐hexene and thus showed a lower value of χ compared to MT–LLDPEs. The Flory–Huggins interaction parameter χ, or the solubility of 1‐hexene at a given temperature and pressure, was suggested as a sensitive measure for the composition distribution of LLDPEs. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1566–1571, 2002; DOI 10.1002/app.10418     

外给电子体对MgCl2负载TiCl4催化剂催化乙烯/丙烯共聚合的影响

采用邻苯二甲酸二异丁酯(DIBP)为内给电子体的Mg Cl2负载Ti Cl4催化剂,考察了在无外给电子体及以环己基甲基二甲氧基硅烷(简称C-donor)、二环戊基二甲氧基硅烷(简称D-donor)、苯基三乙氧基硅烷(简称PTES)为外给电子体的条件下,催化剂对乙烯/丙烯共聚合活性、单体竞聚率、共聚物序列分布和热性能的影响。结果表明,在不同外给电子体作用下,随着乙烯进料比的增加,聚合活性先增加后逐渐减小,并呈现出明显的"共单体效应";DIBP与D-donor有很好的协同效应,二者配合可提高催化剂活性,最高可达8.3 kg(以1 g Ti计);当乙烯/丙烯(摩尔比)为40%~65%时,共聚物链段中乙烯和丙烯分布更均匀,无规度更高,具有更短的平均序列长度;当乙烯/丙烯为50%时,所得共聚物的熔融温度最低,可达108℃,玻璃化转变温度为-48.6℃,表明聚合物具有较好的耐低温性能。     

二氧化碳和丙烯直接合成甲基丙烯酸Ni2(OCH3)2/SiO2催化剂的研究

采用表面改性法制备了负载型Ni2(OCH3)2／SiO2双核金属甲氧基配合物催化剂,利用IR、DSC、TPD和微反技术对催化剂的表面结构、化学吸附性质和催化活性进行了研究。结果表明,负载型双核金属甲氧基配合物Ni2(OCH3)2／SiO2中Ni^2 与载体SiO2表面O^2-以双齿配位形式键合;二氧化碳在催化剂表面存在桥式吸附态和甲氧碳酸酯基物种两种吸附态,丙烯则只有一种吸附态;在适宜反应条件下,CO2和丙烯在Ni2(OCH3)2／SiO2催化剂上可以高选择性地合成甲基丙烯酸,反应物分子共吸附于催化剂表面同一活性单元以及羧酸根与丙烯解离吸附态的形成是反应顺利进行关键因素．     

硅胶负载硫酸铈催化合成苯乙醛缩乙二醇

以苯乙醛和乙二醇为原料,以硅胶负载硫酸铈(Ce2(SO4)3/S iO2)为催化剂,合成了苯乙醛缩乙二醇,考察了醛醇摩尔比、反应时间、催化剂用量及其稳定性等因素对收率的影响。实验结果表明,较优反应条件为:苯乙醛0.1 mol,n(苯乙醛)∶n(乙二醇)=1.0∶1.5,催化剂用量0.2 g,带水剂环己烷12 mL,回流反应2.0 h,苯乙醛缩乙二醇的产率可达96.0%以上。     

Studies on VOCl3/MgCl2/NaY/Al2Et3Cl3 complex support catalysts for the copolymerization of ethylene and propylene

Using VO²⁺ as a spin probe, a new method to obtain microenvironmental information on supports was developed which can be used in the choice of supports for coordination catalysts. Utilizing the above method, NaY was chosen as second support component. A complex support catalyst VOCl₃/MgCl₂/NaY/Al₂Et₃Cl₃ was prepared and used in ethylene–propylene copolymerization. Higher polymerization activity was obtained with this catalytic system. Alternating the ratio of two kinds of supports, the composition and sequence structure of copolymers could be controlled, which showed that NaY participated in the active species, affected the insertion of monomer, and changed the composition and sequence structure of copolymers. © 1994 John Wiley & Sons, Inc.     

用于烯烃均聚和共聚的新型催化剂 VO(P204)2/Et3Al2Cl3

研究了VO(P204)2配合物与Et3Al2Cl3,组成的催化剂作用下的乙烯均聚和乙烯／丙烯共聚。VO(P204)2催化剂聚合乙烯的活性及其活性中心的寿命均高于VOCl3催化剂,并具有良好的氢调敏感性,既可使乙烯、丙烯进行无规共聚,又可使乙烯、丙烯和乙叉降冰片烯进行三元共聚。     

Al_2(SO_4)_3/SiO_2催化高酸值生物柴油原料降酸值研究

通过溶胶-凝胶法和浸渍法制备了二氧化硅负载的硫酸铝催化剂,并测试其在油酸与甲醇酯化反应中的活性,进行高酸值生物柴油原料酯化降酸的研究,考察了催化剂的焙烧温度、硫酸铝的负载量、醇酸比、催化剂用量、反应温度、反应时间及重复利用性等因素对油酸转化率的影响。结果表明,二氧化硅负载的硫酸铝催化剂在油酸和甲醇的酯化反应中具有良好的催化性能。在n(甲醇)∶n(油酸)=8,m(20-Al2(SO4)3/SiO2(500))∶m(油酸)=0.075,反应温度65℃和反应时间为180 min的条件下,油酸的转化率达到92.9%。油酸和甲醇在Al2(SO4)3/SiO2固体酸催化剂的酯化反应符合准一级反应动力学方程,表观活化能为41.56 kJ/mol,指前因子为3.52×104min-1。     

Ring-opening homo- and copolymerization of lactones. Part 1. Homo- and copolymerization of racemic β-butyrolactone with ε-caprolactone and δ-valerolactone by tetraisobutyldialuminoxane (TIBAO) catalyst

Copolymers of racemic β-butyrolactone (β-BL) with ε-caprolactone (ε-CL) (P(BL-co-CL)) and δ-valerolactone (δ-VL) (P(BL-co-VL)) were prepared by ring-opening polymerization reactions using the commercial aluminoxane catalyst tetraisobutyldialuminoxane (TIBAO). The yields, molecular weights, compositions and crystallinities were determined for both copolymers by gel permeation chromatography (GPC), nuclear magnetic resonance (¹H NMR) spectroscopy and differential scanning calorimetry (DSC). A detailed study by ¹³C NMR spectroscopy has been made to determine monomer diad sequence distributions. These results and those of reactivity ratios indicate that the co-polymers may consist of compatible blocks of BL units and VL units of variable size. © 1998 SCI.     

Ti(OBu)_4/TiO_2-Al_2O_3催化合成聚(己二酸-1,4-丁二醇)酯

用Ti(OBu)4/TiO2-Al2O3催化剂合成了聚(己二酸-1,4-丁二醇)酯。Ti(OBu)4/TiO2-Al2O3合成聚(己二酸-1,4-丁二醇)酯的最佳反应条件:催化剂载体焙烧温度为750℃,焙烧时间为4 h,催化剂加入量为1.5%,n(己二酸)/n(1,4-丁二醇)=1∶(1.2~1.3),反应温度为165~170℃,反应时间4 h,在此条件下得到聚酯,酯化率为93.02%,Mn=3 080,Mn/Mw=1.206,催化剂可反复使用5次。     

Supported dicopper(II) complex catalyst Cu2(II)(μ-Br)2/SiO2: synthesis, characterization and catalytic properties for synthesis of ethylene carbonate

A μ-Br-bridged dicopper(II) complex, namely [Cu₂(μ-Br)₂·6H₂O](ClO₄)₂, has been prepared by metal ion grafting. A supported complex catalyst Cu₂(II)(μ-Br)₂/SiO₂was prepared by modifying the silica surface with NaOEt and anchoring the dicopper(II) complex precursor on the surface of the support. The structure of the complex catalyst has been characterized by elemental analysis, IR spectra and UV–VIS diffusion reflection spectra. Obtained data were compared with published data of the complex. TPD-MS and TPD-IR investigations indicated that CO₂ and ethylene oxide (EO) can be chemisorbed on the surface of the catalyst reversibly in a bridged state and can be desorbed from the surface at 105 and 115 K, respectively. In the high temperature range of 450–573 K, another reversible absorption state for CO₂ was also discovered. For EO, however, a decomposition absorption state was found which gave the dissociated species of CH₄ and CO. TPSR-MS experiments have shown that CO₂ and EO reacted on the surface effectively in the range of 343–413 K. An in situ IR method has been used to study the reactivity of the reactants on the surface of the catalyst, and the target product ethylene carbonate (EC) was detected in the range of 333–413 K. Catalytic experiments indicated that the one-way yield of EC is greater than 8.0% and that the selectivity of EC is greater than 82%. A synergic cyclization reaction pathway is proposed to account for the observed products.     

Synthesis of magnetic Pb/Fe3O4/SiO2 and its catalytic activity for propylene carbonate synthesis via urea and 1,2-propylene glycol

To facilitate the recovery of Pb/SiO₂ catalyst, magnetic Pb/Fe₃O₄/SiO₂ samples were prepared separately by emulsification, sol-gel and incipient impregnation methods. The catalyst samples were characterized by means of X-ray diffraction and N₂ adsorption-desorption, and their catalytic activity was investigated in the reaction for synthesizing propylene carbonate from urea and 1,2-propylene glycol. When the gelatin was applied in the preparation of Fe₃O₄ at 60°C and the pH value was controlled at 4 in the preparation of Fe₃O₄/SiO₂, the Pb/Fe₃O₄/SiO₂ sample shows good catalytic activity and magnetism. Under the reaction conditions of a reaction temperature of 180°C, reaction time of 2 h, catalyst percentage of 1.7 wt-% and a molar ratio of urea to PG of 1:4, the yield of propylene carbonate attained was 87.7%.     

Homo- and copolymerization of 5-ethylidene-2-norbornene with ethylene by [2-C5Me4-4,6-Bu2C6H2O]TiCl2/AlBu3/Ph3CB(C6F5)4 catalyst system and epoxidation of the resulting copolymer

5-Ethylidene-2-norbornene (ENB) polymerization and copolymerization with ethylene (E) catalyzed by constrained geometry catalyst 2-tetramethylcyclopentadienyl-4,6-di-tert-butylphenoxytitanium dichloride (1) were studied in the presence of AlⁱBu₃ and Ph₃CB(C₆F₅)₄ (TIBA/B). The catalyst system shows moderate activity on the homopolymerization of ENB, and higher activity on the copolymerization of E/ENB under atmospheric pressure of ethylene. ¹H NMR analysis indicates that ENB was regioselectively incorporated into the copolymer backbone through the endocyclic double bond, leaving the ethylidene double bond unreacted. The ethylidene group contained in the poly(E-co-ENB) was quantitatively converted to the epoxy group with m-chloroperbenzoic acid, producing functionalized poly(E-co-ENB)s. The parent and functionalized copolymers have been characterized using IR, NMR, DSC, and GPC techniques.     

Synthesis, characterization and catalytic activity for NO–CO reaction of Pd–(La, Sr)2MnO4 system

La_xSr_2−xMnO₄ (0 ≤ x ≤ 0.8) oxides were synthesized and single-phase K₂NiF₄-type oxides were obtained in the range of 0.1 ≤ x < 0.5. The catalytic activity of La_xSr_2−xMnO₄ for NO–CO reaction increased with increasing x in the range of solubility limit of La. La_0.5Sr_1.5MnO₄ showed the highest activity among La_xSr_2−xMnO₄ prepared in this study, but its activity was inferior to perovskite-type La_0.5Sr_0.5MnO₃. Among the Pd-loaded catalysts, however, Pd/La_0.8Sr_1.2MnO₄ showed the higher activity and the selectivity to N₂ than Pd/La_0.5Sr_0.5MnO₃ and Pd/γ-Al₂O₃. The excellent catalytic performance of Pd/La_0.2Sr_1.2MnO₄ could be ascribable to the formation of SrPd₃O₄ which was detected by XRD in the catalyst but not in the other two catalysts.     

The effect of sodium on the catalytic activity of ZnO–Al2O3/ZSM-5 and SnO–Al2O3/ZSM-5 for the transesterification of vegetable oil with methanol

In order to elucidate the effect of sodium on the activity of ZSM-5 supported metal oxides catalysts (ZnO–Al₂O₃/ZSM-5 and SnO–Al₂O₃/ZSM-5) for the transesterification of soybean oil with methanol, ZSM-5 supported metal oxides were prepared with and without sodium hydroxide by impregnation. The metal compositions of the ZSM-5 supported metal oxide catalysts and the metal concentrations dissolved from the catalysts to the methylester phase were measured by SEM-EDS and inductive coupled plasma spectroscopy, respectively. The catalytic activity of ZnO–Al₂O₃/ZSM-5 and SnO–Al₂O₃/ZSM-5 containing sodium did not originate from surface metal oxides sites, but from surface sodium sites or dissolved sodium leached from the catalyst surface.     

A Novel Catalyst Pt/CoAl2O4/Al2O3 for Combination CO2 Reforming and Partial Oxidation of CH4

Pt/CoAl₂O₄/Al₂O₃, Pt/CoO_x/Al₂O₃, CoAl₂O₄/Al₂O₃ and CoO_x/Al₂O₃ catalysts were studied for combination CO₂ reforming and partial oxidation of CH₄. The results indicate that Pt/CoAl₂O₄/Al₂O₃ is the most effective, and XRD results indicate that Pt species are well dispersed over the Pt/CoAl₂O₄/Al₂O₃. High dispersion is related to the presence of CoAl₂O₄, formed during calcining at high temperature before Pt addition. In the presence of Pt, CoAl₂O₄ in the catalyst could be reduced partially at 973 K. Based on these results, it appears that zerovalent platinum with high dispersion and zerovalent cobalt resulting from CoAl₂O₄ reduction are responsible for high activity in the Pt/CoAl₂O₄/Al₂O₃ catalyst.     

NO Reduction with CO in the Presence of O2 over Cu/Al2O3 (3) – Structural Analysis of Active Species by Means of XAFS and UV/VIS/NIR Spectroscopy

The local structure around Cu supported on Al₂O₃ was determined by UV/VIS/NIR and XAFS spectroscopic techniques. The relationship between catalytic performance for NO–CO–O₂ reaction and the state of supported Cu species is discussed. A new method for estimating the fraction of aggregated to isolated Cu species is proposed.     

Melamine-(H2SO4)3/melamine-(HNO3)3 instead of H2SO4/HNO3: a safe system for the fast oxidation of thiols and sulfides under solvent-free conditions

Melamine reacted with neat sulfuric acid and fuming nitric acid readily to form two new organic solid acids, namely melamine-(H₂SO₄)₃ and melamine-(HNO₃)₃. Mixture of them acts as a unique powerful system instead of a hazardous H₂SO₄/HNO₃ system for the direct oxidation of thiols. Also, this system can oxidize the sulfides in the presence of a catalytic amount of KBr and few drops of water. This procedure offers advantages such as very low reaction time, simple work-up, excellent yield and matching with some green chemistry protocols.     

Preparation and electrochemical performance studies on Cr-doped Li3V2(PO4)3 as cathode materials for lithium-ion batteries

Cr-doped Li₃V_2−xCr_x(PO₄)₃/C (x = 0, 0.05, 0.1, 0.2, 0.5, 1) compounds have been prepared using sol–gel method. The Rietveld refinement results indicate that single-phase Li₃V_2−xCr_x(PO₄)₃/C with monoclinic structure can be obtained. Although the initial specific capacity decreased with Cr content at a lower current rate, both cycle performance and rate capability have excited improvement with moderate Cr-doping content in Li₃V_2−xCr_x(PO₄)₃/C. Li₃V_1.9Cr_0.1(PO₄)₃/C compound presents an initial capacity of 171.4 mAh g⁻¹ and 78.6% capacity retention after 100 cycles at 0.2C rate. At 4C rate, the Li₃V_1.9Cr_0.1(PO₄)₃/C can give an initial capacity of 130.2 mAh g⁻¹ and 10.8% capacity loss after 100 cycles where the Li₃V₂(PO₄)₃/C presents the initial capacity of 127.4 mAh g⁻¹ and capacity loss of 14.9%. Enhanced rate and cyclic capability may be attributed to the optimizing particle size, carbon coating quality, and structural stability during the proper amount of Cr-doping (x = 0.1) in V sites.     

Low temperature solid-state synthesis routine and mechanism for Li3V2(PO4)3 using LiF as lithium precursor

Monoclinic lithium vanadium phosphate, Li₃V₂(PO₄)₃, has been successfully synthesized using LiF as lithium source. The one-step reaction with stoichiometric composition and relative lower sintering temperature (700 °C) has been used in our experimental processes. The solid-state reaction mechanism using LiF as lithium precursor has been studied by X-ray diffraction and Fourier transform infrared spectra. The Rietveld refinement results show that in our product sintered at 700 °C no impurity phases of VPO₄, Li₅V(PO₄)₂F₂, or LiVPO₄F can be detected. The solid-state reaction using Li₂CO₃ as Li-precursor has also been carried out for comparison. X-ray diffraction patterns indicate that impurities as Li₃PO₄ can be found in the product using Li₂CO₃ as Li-precursor unless the sintering temperatures are higher than 850 °C. An abrupt particle growth (about 2 μm) has also been observed by scanning electron microscope for the samples sintered at higher temperatures, which can result in a poor cycle performance. The product obtained using LiF as Li-precursor with the uniform flake-like particles and smaller particle size (about 300 nm) exhibits the better performance. At the 50th cycle, the reversible specific capacities for Li₃V₂(PO₄)₃ measured between 3 and 4.8 V at 1C rate are found to approach 147.1 mAh/g (93.8% of initial capacity). The specific capacity of 123.6 mAh/g can even be hold between 3 and 4.8 V at 5C rate.