Influence of nanodispersed hydrotalcite on polypropylene photooxidation

Nanocomposites containing hydrotalcite and prepared by melt compounding with polypropylene were UV-light irradiated in artificial accelerated conditions representative of solar irradiation (λ > 300 nm) at 60 °C in air. The chemical modifications resulting from photooxidation were followed by IR and UV-visible spectroscopies.The presence of hydrotalcite was shown to change the global rate of photooxidation of polypropylene by reducing the oxidation induction time and increasing the oxidation rate. The differences of the oxidation induction time disappeared after solvent extraction of the antioxidant. They were attributed to a quenching of the antioxidant activity resulting from a migration onto the filler surface induced by the preferential interaction with the polar hydrotalcite. Extracting the antioxidant did not change the oxidation rate at the permanent regime. The increase of the oxidation rate was attributed to transition metal ions, present as impurities in hydrotalcite, which can accelerate the oxidation of the polymer by various mechanisms including a catalysed decomposition of hydroperoxides.     

Research Progress in the Field of Adsorption and Catalytic Degradation of Sewage by Hydrotalcite‐Derived Materials

With the rapid development of industry and agriculture and the greatly improved living conditions, the resultant gradually deteriorated environments threaten the human beings. Refractory or even toxic pollutants, which are from different industries such as printing and dyeing, pesticides, chemicals, petrochemicals, plastics and rubber, seriously threat the ecosystems and human health. Having the advantages of flexible composition, unique structure, high stability, memory effect, easy preparation and low cost, hydrotalcite compounds have a great potential in sewage degradation and environmental protection. This study focuses on the adsorption and catalytic properties (such as photocatalysis, electrocatalysis and photoelectrocatalysis) of hydrotalcite‐derived materials for treating organic, inorganic and heavy metal ion sewage. The types of adsorption and catalysis, and the effects of various influencing factors on the degradation efficiency were discussed as well.     

Metal–Support Cooperative Catalysts for Environmentally Benign Molecular Transformations

Metal–support cooperative catalysts have been developed for sustainable and environmentally benign molecular transformations. The active metal centers and supports in these catalysts could cooperatively activate substrates, resulting in high catalytic performance for liquid‐phase reactions under mild conditions. These catalysts involved hydrotalcite‐supported gold and silver nanoparticles with high catalytic activity for organic reactions such as aerobic oxidation, oxidative carbonylation, and chemoselective reduction of epoxides to alkenes and nitrostyrenes to aminostyrenes using alcohols and CO/H₂O as reducing reagents. This high catalytic performance was due to cooperative catalysis between the metal nanoparticles and basic sites of the hydrotalcite support. To increase the metal–support cooperative effect, core–shell nanostructured catalysts consisting of gold or silver nanoparticles in the core and ceria supports in the shell were designed. These core–shell nanocomposite catalysts were effective for the chemoselective hydrogenation of nitrostyrenes to aminostyrenes, unsaturated aldehydes to allyl alcohols, and alkynes to alkenes using H₂ as a clean reductant. In addition, these solid catalysts could be recovered easily from the reaction mixture by simple filtration, and were reusable with high catalytic activity.     

Synthesis and thermal stability of hydrotalcites based upon gallium

Hydrotalcites based upon gallium as a replacement for aluminium in hydrotalcite over a Mg/Al ratio of 2:1 to 4:1 were synthesised. The d(003) spacing varied from 7.83 Å for the 2:1 hydrotalcite to 8.15 Å for the 3:1 gallium containing hydrotalcite. A comparison is made with the Mg/Al hydrotalcite in which the d(003) spacing for the Mg/Al hydrotalcite varied from 7.62 Å for the 2:1 Mg hydrotalcite to 7.98 Å for the 4:1 hydrotalcite. The thermal stability of the gallium containing hydrotalcite was determined using thermogravimetric analysis. Four mass loss steps at 77, 263–280, 485 and 828 °C with mass losses of 10.23, 21.55, 5.20 and 7.58% are attributed to dehydration, dehydroxylation and decarbonation. The thermal stability of the gallium containing hydrotalcite is slightly less than the aluminium hydrotalcite.     

Highly Active Supported Pt Nanocatalysts Synthesized by Alcohol Reduction towards Hydrogenation of Cinnamaldehyde: Synergy of Metal Valence and Hydroxyl Groups

The hydrogenation of α,β‐unsaturated aldehydes to allylic alcohols or saturated aldehydes provides a typical example to study the catalytic effect on structure‐sensitive reactions. In this work, supported platinum nanocatalysts over hydrotalcite were synthesized by an alcohol reduction method. The Pt catalyst prepared by the reduction with a polyol (ethylene glycol) outperforms those prepared with ethanol and methanol in the hydrogenation of cinnamaldehyde. The selectivity towards the C=O bond is the highest over the former, although its mean size of Pt particles is the smallest. The hydroxyl groups on hydrotalcite could act as an internally accessible promoter to enhance the selectivity towards the C=O bond. The optimal Pt catalyst showed a high activity with an initial turnover frequency (TOF) of 2.314 s^?1. This work unveils the synergic effect of metal valence and in situ promoter on the chemoselective hydrogenation, which could open up a new direction in designing hydrogenation catalysts.     

Studies on Thermal Stability and Fluid Property of PVC Filled with Hydrotalcite

IntroductionIt is well known that PVC is a kind of valuableplastic and used in many fields.But PVC isunstable against heat and light,and at the heat-molding step,the thermal decomposition of it maytake place.Finally,the decomposition will reducethe mechanical strength and lose otherproperties ofPVC.In order to overcome those disadvantages,athermal stabilizer is added in the PVC material toreduce the thermal decomposition,and organiccompounds of metals such as Sn,Pb,Ca,Ba,Znand Cd are u…     

Preparation of supported metal catalysts starting from hydrotalcites as the precursors and their improvements by adopting “memory effect”

Hydrotalcite-like compounds (HTlcs) can be used as the catalysts as it is since they contain various transition metal cations as the catalytically active species well dispersed on the basic support materials. Moreover, increasing numbers of the applications of HTlcs after the heat treatment have been found since the oxides with very small crystal size, stable to thermal treatments, are obtained after the calcination. The oxides possess interesting properties such as high surface area, basic properties and further form small and thermally stable metal crystallites by reduction. Moreover, the calcined oxides show a unique property, i.e., “memory effect,” which allows the reconstitution of the original hydrotalcite structure. We have developed the catalytic applications of hydrotalcites as it is and moreover the mixed oxides derived from hydrotalcites for various catalytic reactions, i.e., oxidation, dehydrogenation and reforming of hydrocarbons, and even for the reforming of methanol and the CO shift reaction. Aerobic oxidation of alcohols, Baeyer−Villiger oxidation of ketones and O₃ oxidation of oxalic acid have been successfully carried out with the Mg−Al hydrotalcites containing Ni, Fe and Cu, respectively, as the catalysts in liquid phase. In the O₃ oxidation of oxalic acid, the catalytic activity was enhanced by the “memory effect,” i.e., Mg(Cu)–Al hydrotaclite was reconstituted on the surface of Mg(Cu,Al)O periclase particles and oxalic acid was incorporated as anions in the hydrotalcite layer, resulting in an enhanced oxidation of oxalic acid. As the catalysts in the vapor phase reactions, Mg/Fe/Al mixed oxides prepared from Mg–Al(Fe) hydrotalcites and effectively catalyzed the dehydrogenation of ethylbenzene. Supported Ni metal catalysts have been prepared from Mg(Ni)–Al hydrotalcites and successfully used in the steam reforming and the oxidative reforming of methane and propane. Moreover, the Ni catalysts have been improved by combining a trace amount of noble metals by adopting the “memory effect” and used in the production of hydrogen for the PEFC under the daily startup and shutdown operation. Also starting from aurichalcite or hydrotalcite precursor as the precursor, Cu/Zn/Al catalysts with high Cu metal surface area have been prepared and successfully applied in the steam reforming of methanol and dimethyl ether, and moreover in the CO shift reaction.     

花球状镁铝复合氧化物负载Ni⁃Co催化剂的合成及正十二烷水蒸气重整制氢

采用水热晶化的方法制备了花球状镁铝层状水滑石材料,经过高温焙烧和氢气还原成功制备了镁铝复合氧化物负载的Ni?Co合金催化剂。通过扫描电子显微镜、透射电子显微镜、氮气吸附-脱附测试、粉末X射线衍射、程序升温还原等技术表征了所制备催化剂的物理化学性质,并且测试了所制备催化剂催化正十二烷水蒸气重整制氢性能。实验结果表明:水热晶化后催化剂的前驱体是花球状层状水滑石结构,焙烧后催化剂以复合氧化物的结构存在,且存在非常丰富的介孔和大孔。通过调控Co的加入量,可以调控金属载体相互作用的强度及金属颗粒尺寸。还原后,Ni和Co形成合金且均匀地分布在层状薄片镁铝复合氧化物上面。所制备的催化剂用于正十二烷水蒸气重整制氢,结果显示,相比于Ni单金属催化剂,形成Ni?Co合金的催化剂的活性及产氢率均有较大程度的提升,且抗积碳性能大幅度提高。这归因于Ni?Co协同的合金状态和较小的金属纳米颗粒尺寸。     

Nitrate absorption through hydrotalcite reformation

Thermally activated hydrotalcite based upon a Zn/Al hydrotalcite with carbonate in the interlayer has been used to remove nitrate anions from an aqueous solution resulting in the reformation of a hydrotalcite with a mixture of nitrate and carbonate in the interlayer. X-ray diffraction of the reformed hydrotalcites with a d(003) spacing of 7.60 A shows that the nitrate anion is removed within a 30 min period. Raman spectroscopy shows that two types of nitrate anions exist in the reformed hydrotalcite (a) nitrate bonded to the 'brucite-like' hydrotalcite surface and (b) aquated nitrate anion in the interlayer. Kinetically the nitrate is replaced by the carbonate anion over a 21 h period. Two types of carbonate anions are observed. This research shows that the reformation of a thermally activated hydrotalcite can be used to remove anions such as nitrate from aqueous systems.     

尿素法合成高结晶度类水滑石

尿素的高温分解特性被用于控制层状化合物合成过程中的pH值。室温下尿素可与硝酸盐形成均一溶液，当其高温分解时可以保证溶液内部各点的pH值始终一致，因而可获得高结晶度的水滑石样品。利用该法可合成出Mg-Al、Zn-Al及Ni-Al类水滑石，但难以合成出Co-Al，Mn-Al及Co-Cr类水滑石，相信这与不同金属离子发生沉淀时所需的pH值有关。     

Thermal decomposition of hydrotalcite with molybdate and vanadate anions in the interlayer

Hydrotalcites containing carbonate, vanadate and molybdate were prepared by coprecipitation. The resulting materials were characterized by XRD, and TG/DTA to determine the stability of the hydrotalcites synthesized. The thermal decomposition of carbonate hydrotalcites consist of two decomposition steps between 300 and 400°C, attributed to the simultaneous dehydroxylation and decarbonation of the hydrotalcite lattice. Water loss ascribed to dehydroxylation occurs in two decomposition steps, where the first step is due to the partial dehydroxylation of the lattice, while the second step is due to the loss of water interacting with the interlayer anions. Dehydroxylation results in the collapse of the hydrotalcite structure to that of its corresponding metal oxides, including MgO, Al₂O₃, MgAl₂O₄, NaMg₄(VO₄)₃ and Na₂Mg₄(MoO₄)₅. The presence of oxy-anions proved to be beneficial in the stability of the hydrotalcite structure, shown by the delay in dehydroxylation of oxy-anion containing hydrotalcites compared to the carbonate hydrotalcite. This is due to the substantial amount of hydroxyl groups involved in a network of hydrogen bonds involving the intercalated anions. Therefore, the stability of the hydrotalcite structure appears to be dependent on the type of anion present in the interlayer. The order of thermal stability for the synthesized hydrotalcites in this study is Syn-HT-V>Syn-HT-Mo> Syn-HT-CO₃-V>Syn-HT-CO₃-Mo>Syn-HT-CO₃. Carbonate containing hydrotalcites prove to be less stable than oxy-anion only hydrotalcites.     

Flammability characteristics and synergistic effect of hydrotalcite with microencapsulated red phosphorus in halogen-free flame retardant EVA composite

The flammability characteristics and synergistic effect of hydrotalcite with microencapsulated red phosphorus (MRP) in halogen-free flame retardant ethylene vinyl acetate (EVA) composite have been studied by cone calorimeter test (CCT), thermogravimetric analysis (TGA), limiting oxygen index (LOI) and UL-94 test. The results obtained by comparing the flame retardancy of hydrotalcite with magnesium hydroxide (MH) and aluminium hydroxide (AH) for their EVA composites showed that hydrotalcite has higher flame retardant effect than MH and AH at the same loading level. The CCT tests indicated that the heat release rate (HRR) and mass loss rate (MLR) of EVA composite blended with hydrotalcite greatly decreased compared with those blended with MH and AH. The LOI values of EVA/hydrotalcite composites are 3-4% higher than those of the corresponding MH composites at 40-60 wt% loading levels, and 6% higher than that of the corresponding AH composite at 40 wt% loading level. Moreover, the addition of a given amount of MRP apparently resulted in the increase of LOI value and decrease of the HRR and MLR as well the loading of hydrotalcite in EVA blend while keeping the V-0 rating in UL-94 test. However, the smoke release increased during the combustion of EVA/hydrotalcite blend containing MRP.     

Biodiesel Preparation from Jatropha curcas Oil Catalyzed by Hydrotalcite Loaded With K2CO3

This paper discusses the synthesis of biodiesel catalyzed by solid base of K₂CO₃/HT using Jatropha curcas oil as feedstock. Mg–Al hydrotalcite was prepared using co-precipitation methods, in which the molar ratio of Mg to Al was 3:1. After calcined at 600 °C for 3 h, the Mg–Al hydrotalcite and K₂CO₃ were grinded and mixed according to certain mass ratios, in which some water was added. The mixture was dried at 65 °C, and after that it was calcined at 600 °C for 3 h. Then, this Mg–Al hydrotalcite loaded with potassium carbonate was obtained and used as catalyst in the experiments. Analyses of XRD and SEM characterizations for catalyst showed the metal oxides formed in the process of calcination brought about excellent catalysis effect. In order to achieve the optimal technical reaction condition, five impact factors were also investigated in the experiments, which were mass ratio, molar ratio, reaction temperature, catalyst amount and reaction time. Under the best condition, the biodiesel yield could reach up to 96%.     

镁铁和镁铁铝催化剂氢还原过程的研究

以水滑石为前体 ,制备了镁铁和镁铁铝复合氧化物催化剂 ,运用原位穆斯堡尔谱研究了催化剂在H2 气氛中的还原行为。结果表明 :由于Mg、Al的加入和固溶体的形成 ,相对地稳定了FeO物相 ,阻碍了H2 对铁离子的还原 ,使得Fe2 进一步还原为金属Fe0 的能力减弱 ;在还原过程中催化剂首先生成含Fe2 的固溶体FeO MgO或FeO MgO Al2O3,然后再完全还原成金属Fe0。     

NOx的催化分解研究

氮氧化物(NO_x)的直接催化分解是公认的消除NO_x污染最有吸引力的方法。本文综述了NO_x催化分解研究领域深受关注的几类催化剂,包括贵金属、金属氧化物、钙钛矿及类钙钛矿型复合氧化物、离子交换的ZSM-5型分子筛、杂多化合物和水滑石类材料等六大类催化剂。介绍了相关的反应机理、反应动力学和催化性能等问题的国内外研究进展,概括了上述催化剂的优缺点,提出了未来的发展方向。     

高结晶度镍铝水滑石的制备及其电化学行为研究

水滑石(Hydrotalcite,简称HT)是一类层状结构的阴离子粘土,它具有碱性特征、微孔结构、记忆效应及金属离子的同晶可取代性和层间阴离子的可交换性.此外,由于它具有材料廉价易得,独特的离子交换性能,很好的热和化学稳定性等特点,使其在电分析方面作为安培传感器~([1])、电位传感器~([2])、生物传感器~([3])以及作为超级电容器的电极活性材料~([4-6])刮都有潜在应用价值.     

Mg-Al-CO_3与Zn-Al-CO_3水滑石热稳定性差异的研究

层状双金属氢氧化物（ Layered double hydroxides,简称 LDHs）是一类近年来发展迅速的阴离子型粘土,又称水滑石,其组成通式为： [M? 1-xM? x(OH)2]x＋ Ax/nn-mH2O,其中 M?是二价金属离子, M?是三价金属离子, An－是阴离子。这种材料是由相互平行的层板组成,层板带有永久正电荷;层间具有可交换的阴离子以维持电荷平衡。通过离子交换可在层间嵌入不同的基团,制备许多功能材料,被广泛用作催化剂、吸附剂及油田化学品等,已引起人们的关 注 [1～ 4]。有关 Mg-Al-CO3与 Zn-Al-CO3水滑石的合成及性能研究国内外已有大量报道 [1…     

Adsorption and separation of proteins by a synthetic hydrotalcite

In this study, the potential use of a synthetic Mg/Al hydrotalcite (layered double hydroxide) as a novel chromatography material for protein purification was investigated. The hydrotalcite is present in its carbonate form and is characterized by an Al/Mg-ratio of 1.85. Zetapotential measurements confirm a positive surface potential up to pH 10 suggesting applicability as anion exchanger. The binding of model proteins covering a broad range of isoelectric points and molecular weights was performed at different pH-values under batch conditions to evaluate the binding behaviour of the hydrotalcite. Furthermore, static binding capacities were exemplarily determined for hemoglobin and human serum albumin. Additionally, the adsorption and elution of hemoglobin was studied under dynamic conditions. The binding behaviour of the hydrotalcite was compared to commercially available anion exchangers and was found to be a function of pH, depending on the model protein. Variant adsorption behaviour is explained by further interactions like hydrogen bonds and by an unequal charge distribution over the protein surfaces. The hydrotalcite reveals high adsorption capacities under static (260 mg/g) as well as under dynamic conditions (88 mg/g at 34 cm/h; 61 mg/g at 340 cm/h). With appropriate buffers like 500 mM carbonate (pH 10) the adsorbed proteins can be nearly completely desorbed making regeneration possible. Due to the binding and elution properties it is concluded, that the hydrotalcite can serve anion exchange material for chromatographic protein separations.     

水滑石的插层及其选择性红外吸收性能

离子交换;水滑石的插层及其选择性红外吸收性能     

Zn-Al水滑石催化碳酸二甲酯与苯酚酯交换反应的研究

用共沉淀法制备了Zn-Al水滑石,并用于多相催化酯交换合成碳酸二苯酯的反应.研究了不同n(Zn)/n(Al)比的水滑石及其焙烧产物等对酯交换反应的催化活性.结果表明,Zn-Al水滑石催化剂对该反应的催化活性和选择性很高,当n(Zn)/n(Al)=3时,在150～180℃,n(PhOH)/n(DMC)=2,催化剂用量为反应物总质量的1.5%,在反应时间为12h的条件下,DMC的转化率达到55.9%,DPC和MPC的收率分别为25.3%和27.0%,酯交换产物的选择性达到93.6%.利用XRD,TG-DTA和TEM等手段对催化剂进行了表征.