以Ca-M-Al(M=Mg,La,Ce,Y)层状双氢氧化物为前驱体的固体碱用于酯交换合成碳酸二甲酯（英文）

碳酸二甲酯(DMC)是一种环境友好型绿色化学品,可作为甲基化和羰基化试剂用于取代传统剧毒的硫酸二甲酯和光气.另外,DMC具有良好的溶解性能,可用于高级溶剂;DMC分子中具有高的氧含量,可用作汽油添加剂来提高汽油的辛烷值;DMC还可用作聚碳酸酯的原料.随着人们环保意识的不断增强,DMC的生产和应用呈现出巨大的吸引力和市场潜力.DMC合成方法主要有光气法、甲醇氧化羰化法、尿素醇解法及酯交换法等.酯交换法具有反应条件温和、产率高等优点,是目前工业制备DMC的主要方法.研究发现,相对于酸性催化剂,碱性催化剂更有利于酯交换法合成DMC.金属氧化物催化剂具有活性高、热稳定性高及可连续重复回收利用等优点,因而引起了广泛关注.CaO对于酯交换合成DMC反应具有良好的催化活性,但其稳定性差.因此,通常采用复合金属氧化物来促进CaO的分散,并增加金属间相互作用以防止CaO流失.研究发现,经煅烧后的Mg-Al,Ca-Al和Ca-Mg-Al催化剂对于酯交换反应具有高的活性和稳定性.此外,通过碱性稀土金属(La,Ce和Y)的引入可以修饰催化剂上的碱性位点,从而调变催化剂的碱性.本文合成了一系列以Ca-M-Al(M=Mg,La,Ce,Y)层状双氢氧化物为前驱体的固体碱催化剂,将其用于甲醇与碳酸丙烯酯酯交换合成DMC.通过X射线衍射、热重分析、红外光谱、X射线光电子能谱、电感耦合等离子体、CO_2程序升温脱附和Hammett指示剂对催化剂进行了表征.研究发现,各催化剂的活性高低依次为:Ca-Y-AlCa-AlCa-Ce-AlCa-La-AlCa-Mg-Al,这与催化剂表面总碱量相一致.通过Mg和La的引入,催化剂表面出现了超强碱性位.其中,Ca-Mg-Al催化剂表面具有最高的(Ca+Mg):Al原子比,从而导致催化剂表面产生更多的不饱和O~(2-)离子,因而具有最高的碱性位数量.此外,通过Mg,La,Ce和Y的引入,催化剂的重复使用性能得到了提高.特别是Ca-Mg-Al催化剂,在10次循环后仍保持着高的活性,且其结构没有发生显著变化,表明其稳定性较高,因此该催化剂在非均相催化中具有高的应用价值.     

NaF含量对以水滑石结构为前驱体的固体碱催化剂F-Ca-Mg-Al及碳酸二甲酯合成的影响（英文）

以碳酸丙烯(PC)和甲醇为原料,经酯交换反应合成的多功能、环保的碳酸二甲酯(DMC)是一种绿色、节能的合成方法。CaO固体碱催化剂对该反应具有良好的催化性能,但其再生性不理想。以F-Ca-Mg-Al水滑石(LDHs)为原料,制备了一系列不同Na F用量的固体碱催化剂,并对其进行了表征和酯交换反应测试。与不加氟的FCMA-0催化剂相比,经氟改性后的催化剂的比表面积、碱量、催化活性等性能均有明显提高。催化活性由高到低依次为:FCMA-0.8> FCMA-0.4>FCMA-1.2> FCMA-1.6> FCMA-0,这与总碱位量和强碱位量一致。FCMA-0.8催化剂活性最好,与纯CaO催化剂的相当,PC转化率为66.8%,DMC选择性为97.4%,DMC收率为65.1%。在10次循环使用后,FCMA-0.8催化剂的DMC收率仅下降3.9%(CaO催化剂下降33.2%)。FCMA-0.8在PC与甲醇酯交换制DMC方面具有良好的工业应用前景。     

过渡金属改性Mg-Al基固体碱催化剂上碳酸丙烯酯与甲醇合成碳酸二甲酯的研究

以共沉淀法制备了一系列不同价态过渡金属(Fe、Cu、Zr)改性的Mg-Al固体碱催化剂,考察了其对于甲醇与碳酸丙烯酯(PC)酯交换合成碳酸二甲酯的反应性能。采用XRD、N₂吸附-脱附、FT-IR、XPS、CO₂-TPD等手段对催化剂的物理化学性质进行了表征。结果表明,催化剂的碱强度、碱密度是影响催化活性的主要因素,不同价态过渡金属的加入可以调控Mg-Al固体催化剂的碱性。在考察的催化剂中,FeMgAl催化剂具有最高的表面碱密度,因此,表现出最好的催化性能。在温度为65℃、时间为4 h、甲醇与PC物质的量比为10∶1、催化剂用量为4%的反应条件下,PC转化率可达66.2%。     

Mg-Al-Ti层状双氢氧化物的零电荷点和界面酸-碱反应平衡常数

采用共沉淀法, 固定Mg²⁺/(Al³⁺+Ti⁴⁺)摩尔比为3.00, 改变Ti⁴⁺/(Al³⁺+Ti⁴⁺)摩尔比（R_Ti, 0~0.40）, 合成了5个Mg-Al-Ti-CO₃层状双氢氧化物（LDHs）样品, 并进行了表征. 采用电势滴定、 盐滴定和电势质量滴定法, 测定了其结构电荷密度（σ_st）、 零净电荷点（pH_PZNC）和零净质子电荷点（pH_PZNPC）等, 并基于普适1-pK和2-pK模型得出其表面羟基酸碱反应特征平衡常数（pK, pK{}_{\mathrm{a}\mathrm{1}}^{\mathrm{i}\mathrm{n}\mathrm{t}}和pK{}_{\mathrm{a}\mathrm{2}}^{\mathrm{i}\mathrm{n}\mathrm{t}}）, 考察了R_Ti对LDHs晶体结构和界面电化学性质的影响. 研究结果表明, 随着R_Ti增大,晶胞常数和层间距均增大, 可归因于Ti⁴⁺离子间强静电排斥作用. pH_PZNC和pH_PZNPC以及pK, pK{}_{\mathrm{a}\mathrm{1}}^{\mathrm{i}\mathrm{n}\mathrm{t}}和pK{}_{\mathrm{a}\mathrm{2}}^{\mathrm{i}\mathrm{n}\mathrm{t}}均随R_Ti的增大而有增大的趋势, 表明表面羟基去质子化趋势降低. 各LDHs样品的pH_PZNPC值低于其pH_PZNC值, 且随电解质（NaNO₃）浓度的增大而升高, 可归因于结构正电荷效应.     

基于层状双氢氧化物前驱体的CO2甲烷化NiAlNd催化剂

采用乙二醇溶剂热法合成了一系列基于层状双氢氧化物前驱体(LDHs)的NiAlNd催化剂。Nd的引入大大提高了CO₂甲烷化的低温催化活性。在 T=210 ℃,WHSV(weight hourly space velocity)=24 000 mL·g^-1·h^-1,p=100 kPa的条件下,NiAlNd-0.4催化剂上CO₂转化率达到83.9%。Nd³⁺取代部分Al³⁺阻碍了前驱体中LDHs结构的形成,同时也减小了焙烧后催化剂的粒径。Nd的加入削弱了NiO与Al₂O₃之间的相互作用,促进了NiO的还原,提高了Ni的本征活性。此外,Nd的添加提高了催化剂表面碱性位的数目,从而增强了对CO₂的吸附。随着Nd掺杂量的增加,还原后的催化剂中金属Ni的表面积呈火山形变化。Ni活性位的数目和本征活性同时影响NiAlNd催化剂的催化活性。     

基于层状双氢氧化物前驱体的CO2甲烷化NiAlNd催化剂

采用乙二醇溶剂热法合成了一系列基于层状双氢氧化物前驱体(LDHs)的NiAlNd催化剂。Nd的引入大大提高了CO₂甲烷化的低温催化活性。在 T=210 ℃,WHSV(weight hourly space velocity)=24 000 mL·g^-1·h^-1,p=100 kPa的条件下,NiAlNd-0.4催化剂上CO₂转化率达到83.9%。Nd³⁺取代部分Al³⁺阻碍了前驱体中LDHs结构的形成,同时也减小了焙烧后催化剂的粒径。Nd的加入削弱了NiO与Al₂O₃之间的相互作用,促进了NiO的还原,提高了Ni的本征活性。此外,Nd的添加提高了催化剂表面碱性位的数目,从而增强了对CO₂的吸附。随着Nd掺杂量的增加,还原后的催化剂中金属Ni的表面积呈火山形变化。Ni活性位的数目和本征活性同时影响NiAlNd催化剂的催化活性。     

交换时间对离子交换法合成谷氨酸/锌铝层状双氢氧化物的结构和热稳定性的影响

采用离子交换法实现了谷氨酸(Glu)插层到ZnAl层状双氢氧化物(ZnAl-LDH)中而形成Glu/ZnAl-LDH纳米复合材料,并用X射线衍射(XRD)、傅里叶变换红外(FT-IR)光谱、透射电子显微镜(TEM)以及热失重-差热(TG-DTA)分析等测试技术,研究了交换时间对Glu/ZnAl-LDH纳米复合材料结构的影响。发现当交换时间为1d时,Glu/ZnAl-LDH纳米复合材料粒子的结晶度好,Glu分子均以垂直形式插入,此时Glu在层间达到交换平衡。当交换时间为2d时,部分Glu开始以水平方式插入ZnAl-LDH纳米材料层间。但当交换时间进一步延长时,ZnAl-LDH纳米材料的结构发生部分坍塌,而且ZnAl-LDH纳米材料在微酸性的Glu溶液中发生部分溶解而使其六边形的结构出现破损。由于Glu插入ZnAl-LDH纳米复合材料层间后,其稳定性得到提高,因此,ZnAl-LDH纳米材料可以作为优良的生物分子的载体和储存器。     

微波晶化法合成纳米Mg-Al型层状双氢氧化物阻燃剂的研究

用微波加热反应-变速滴加共沉淀法合成了粒径约为10～40 nm 的纳米LDHs, 用TEM和XRD对产物进行了表征, 并讨论了微波和变速滴加碱液的方法对纳米层状双氢氧化物的合成的作用. 从纳米层状双氢氧化物的TG, DTG与DSC曲线出发, 采用Ozawa法计算了它的热分解活化能, 据此把纳米层状双氢氧化物的热分解分成四个质量损失阶段. 并对它的热分解过程进行了分析, 提出了它的分解模型. 当采用纳米LDHs对PS, ABS, HDPE和PVC进行阻燃处理时, 可使它们的氧指数分别提高到28, 27, 26和33; 当阻燃涂料中含1.9%的纳米LDHs（加入量为常规TiO₂的0.27倍）时, 其耐火极限可达32 min 45 s, 比以TiO₂为阻燃填料时的最佳耐火极限多7 min 5 s.     

碱性介质中Ni–Fe层状双氢氧化物析氧催化剂的研究进展

电催化水裂解被广泛认为是一种非常有前景的制氢路线之一,这一反应过程包括析氢反应和析氧反应.与析氢反应相比,析氧反应涉及多步质子耦合–电子转移过程,需要较大的活化能垒和过电势,因此是水裂解反应的瓶颈. Ni–Fe层状双氢氧化物因其独特的层状结构和优异的析氧反应性能而备受关注.本文首先介绍了电催化析氧反应的机理以及评价电催化剂性能的关键参数和标准,讨论了Ni–Fe层状双氢氧化物催化剂的制备方法,随后重点综述了析氧反应性能优化策略,如构筑纳米结构、掺杂异原子、构建异质结构、负载单原子、调控缺陷位、扩大层间距等方法.最后,对Ni–Fe LDH催化剂未来发展提出了展望和挑战.     

Synthesis of dimethyl carbonate and propylene glycol from transesterification of propylene carbonate and methanol using quaternary ammonium salt catalysts

Summary The synthesis of dimethyl carbonate (DMC) was investigated through the transesterification of propylene carbonate (PC) with methanol using quaternary ammonium salt catalysts. The reaction was carried out in an autoclave at 120-140 oC under carbon dioxide pressure of 250-400 psig. The main by-product was propylene glycol. The quaternary salts of larger alkyl group and more nucleophilic counter anion exhibited higher catalytic activity. Kinetic studies were also performed to better understand the reaction mechanism. Quaternary ammonium chlorides immobilized on polystyrene supports were also tested for their possible uses as heterogeneous catalysts.     

Dimethyl carbonate synthesis catalyzed by DABCO-derived basic ionic liquids via transesterification of ethylene carbonate with methanol

Easily prepared DABCO-derived (1,4-diazobicyclo[2.2.2]octane) basic ionic liquids were developed for an efficient synthesis of dimethyl carbonate (DMC) via the transesterification of ethylene carbonate (EC) with methanol. 1-Butyl-4-azo-1-azoniabicyclo[2.2.2]octane hydroxide ([C₄DABCO]OH) exhibited high catalytic activity and 81% DMC yield together with 90% EC conversion was obtained under mild reaction conditions. Notably, the catalyst could be recycled for four times without loss of catalytic activity. Moreover, a possible mechanism was also discussed.     

Biodegradable poly(propylene carbonate)/layered double hydroxide composite films with enhanced gas barrier and mechanical properties

Relatively well crystallized and high aspect ratio Mg-Al layered double hydroxides(LDHs) were prepared by coprecipitation process in aqueous solution and further rehydrated to an organic modified LDH(OLDH) in the presence of surfactant. The intercalated structure and high aspect ratio of OLDH were verified by X-ray diffraction(XRD) and scanning electron microscopy(SEM). A series of poly(propylene carbonate)(PPC)/OLDH composite films with different contents of OLDH were prepared via a melt-blending method. Their cross section morphologies, gas barrier properties and tensile strength were investigated as a function of OLDH contents. SEM results show that OLDH platelets are well dispersed within the composites and oriented parallel to the composite sheet plane. The gas barrier properties and tensile strength are obviously enhanced upon the incorporation of OLDH. Particularly, PPC/2%OLDH film exhibits the best barrier properties among all the composite films. Compared with pure PPC, the oxygen permeability coefficient(OP) and water vapor permeability coefficient(WVP) is reduced by 54% and 17% respectively with 2% OLDH addition. Furthermore, the tensile strength of PPC/2%OLDH is 83% higher than that of pure PPC with only small lose of elongation at break. Therefore, PPC/OLDH composite films show great potential application in packaging materials due to its biodegradable properties, superior oxygen and moisture barrier characteristics.     

Selective oxidation of ethylbenzene to acetophenone over Cr(III) Schiff base complex intercalated into layered double hydroxide

A new heterogeneous catalyst, Cr(III) Schiff base‐containing layered double hydroxide, was synthesized using the intercalation method. The Cr(III) Schiff base complex derived from 2‐hydroxy‐1‐naphthaldehyde and 4‐aminobenzoic acid was intercalated into the layered double hydroxide. The synthesized materials were characterized using inductively coupled plasma atomic emission spectrometry, energy‐dispersive X‐ray analysis, scanning electron microscopy, X‐ray diffraction, Brunauer–Emmett–Teller surface area measurement, Fourier transform infrared spectroscopy, thermogravimetric analysis, diffuse reflectance UV–visible spectroscopy and electron paramagnetic resonance spectroscopy. The catalytic activity was investigated for the oxidation of ethylbenzene with tert‐butylhydroperoxide as an oxidant under solvent‐free conditions as well as with lower chromium concentrations. In the oxidation reaction, ethylbenzene was oxidized to acetophenone and benzaldehyde. The catalyst was recycled ten times without significant loss of catalytic activity. Leaching studies performed with hot filtration experiments showed that the chromium catalyst was heterogeneous in nature and stable under the reaction conditions.     

基于层状氢氧化物衍生复合氧载体的生物质化学链气化实验研究

通过低饱和共沉淀法合成了类水滑石结构的层状氢氧化物(Layered Double Hydroxide,LDH)前驱体,经煅烧获得衍生Cu/Al/Zn、Cu/Al/Ni、Cu/Al/Ni/Zn高分散复合氧载体。采用XRD、XRF、H2-TPR、SEM及BET等分析手段对氧载体的结构及反应性能进行了表征,并通过固定床反应器开展了氧载体与生物质化学链气化实验。结果表明,合成的三种前驱体都具有典型的水滑石特征衍射峰,且层板稳定。Cu/Al/Zn前驱体层间厚度为0.264 2 nm,Ni2+引入后,层间距减小。前驱体煅烧后形成的复合氧载体中元素含量与制备试剂基本一致。氧载体中Zn、Ni元素的引入可提升Cu O的反应活性,降低H2还原的反应温度,Zn元素与Cu具有更好的协同作用。Cu/Al/Ni/Zn氧载体在固定床化学链气化中具有较好的碳转化率和气体产率,其碳转化率为82.03%。反应后氧载体比表面积为5.995 m2/g,具有较好的可再生性与抗烧结性,是生物质化学链气化反应较为理想的氧载体。     

Solubility and release of fenbufen intercalated in Mg, Al and Mg, Al, Fe layered double hydroxides (LDH): The effect of Eudragit S 100 covering

Following different preparation routes, fenbufen has been intercalated in the interlayer space of layered double hydroxides with Mg²⁺ and Al³⁺ or Mg²⁺, Al³⁺ and Fe³⁺ in the layers. Well crystallized samples were obtained in most of the cases (intercalation was not observed by reconstruction of the MgAlFe matrix), with layer heights ranging between 16.1 and 18.8 Å. The presence of the LDH increases the solubility of fenbufen, especially when used as a matrix. The dissolution rate of the drug decreases when the drug is intercalated, and is even lower in those systems containing iron; release takes place through ionic exchange with phosphate anions from the solution. Preparation of microspheres with Eudragit^® S 100 leads to solids with an homogeneous, smooth surface with efficient covering of the LDH surface, as drug release was not observed at pH lower than 7.     

Synthesis of dimethyl carbonate (dmc) from co2, ethylene oxide and methanol using heterogeneous anion exchange resins as catalysts

Summary A two-step synthesis of dimethyl carbonate (DMC) from ethylene oxide (EO), carbon dioxide and methanol using heterogeneous anion exchange resins as catalysts is reported. The first step is the reaction of EO with CO₂ to form ethylene carbonate (EC), and the second one the transesterification of EC with methanol to yield DMC. Effect of various reaction parameters on the activity and selectivity of the catalysts used was investigated. After the first step, the crude mixture containing EC was directly reacted with methanol in the presence of a heterogeneous anion exchange resin catalyst to produce DMC in high yield and selectivity. Our process is highly economic.     

助剂M(M=Cr、 Zn、Y、La)对甲醇水蒸气重整制氢CuO/CeO_2催化剂的影响

采用顺序浸渍法制备了掺杂助剂M(M=Cr、Zn、Y、La)的CuO/CeO_2催化剂,并利用XRF、XRD、BET、H_2-TPR和XPS等手段对催化剂进行了表征,考察了不同助剂对CuO/CeO_2催化剂结构、性质和性能的影响。结果表明,助剂的掺杂主要影响CuO/CeO_2催化剂的CuO分散、催化剂的还原性质、CuO与CeO_2间的相互作用和催化剂表面氧空穴含量。掺杂助剂Cr和Zn后,提高了CuO在催化剂表面的分散度,使CuO和CeO_2间的相互作用加强,表面氧空穴增加,进而使得催化活性提高。而掺杂助剂Y和La后,降低了CuO在催化剂表面的分散度,使CuO和CeO_2间的相互作用减弱,表面氧空穴减少,进而使得催化活性降低。其中,掺杂Cr助剂的催化剂催化性能较优,当反应条件为260℃,n(CH_3OH)∶n(H_2O)=1∶1.2,甲醇水蒸气气体空速为1760 h~(-1)时,最终转化率可达100%,重整尾气中CO含量为0.15%,与CuO/CeO_2催化剂相比,转化率提高了10%,重整尾气中CO含量降低了0.34%。     

MnOx/Al2O3/Ce0.45Zr0.45M0.10Oy （M = Mn, Y, La） catalysts used for ethanol catalytic combustion

MnOx/Al2O3/Ce0.45Zr0.45M0.10Oy (M = Mn,Y,La) catalysts were prepared by impregnation method and characterized by BET,TPR and XRD analyses.The catalytic activities toward ethanol combustion were investigated in a microreactor.The results demonstrated that the catalytic activity of MnOx/Al2O3/Ce0.50Zr0.50O2 monolithic catalyst could be improved by doping Mn,Y and La into Ce0.50Zr0.50O2.When doping Y into Ce0.50Zr0.50O2,the catalyst MnOx/Al2O3/Ce0.45Zr0.45Y0.10O1.95 showed the highest activity.The 100% conversion temperature of ethanol was 230 ℃.Furthermore,once the conversion of ethanol started,the complete conversion was quickly achieved.The doping of Mn,Y and La led to better activity for ethanol combustion and lower temperature reduction peaks in TPR profiles.The doping of Mn resulted in enhanced oxygen storage capacity (OSC),larger area of the reduction peaks,and excellent reactivity,and the doping of Y resulted in the lowest reduction temperature and the best activity.